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Our interpretation of photosynthetically active radiation in plants has evolved since the 1970s with new data explaining the underlying mechanisms. To update McCree's founding work, this study explored the spectral response of photosynthesis in young tomato (Solanum lycopersicum cv. Beefsteak) and lettuce (Lactuca sativa cv. Breen) plants using a narrow-spectrum light unit and a portable photosynthesis system equipped with a whole plant chamber. Highly resolved spectral photosynthesis curves using 1-nm increments at 10 nm full width at half maximum (FWHM) were generated. Results show that the lowest quantum yields were observed at 450 nm and 660 nm, two wavelengths commonly used to improve photosynthesis in research. Different trends and amplified peaks were observed among the spectral quantum yield curves of tomato and lettuce plants and those of earlier studies with red and blue light. An opposing phenomenon was observed, where blue light is more efficient than red light. This is based on the narrower wavelength data acquired in both experimental plant species. Findings represent the most detailed and highly resolved spectral photosynthesis and quantum yield curves to date using experimental model plants (tomato and lettuce)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Optimizing photosynthetic lighting is essential for maximizing crop production and minimizing electricity costs in controlled environment agriculture (CEA). Traditional lighting methods often neglect the impact of environmental factors, crop type, and light acclimation on photosynthetic efficiency. To address this, a chlorophyll fluorescence-based biofeedback system was developed to adjust light-emitting diode (LED) intensity based on real-time plant responses, rather than using a fixed photosynthetic photon flux density (PPFD). This study used the biofeedback system to maintain a range of target quantum yield of photosystem II (Φ PSII ) and electron transport rate (ETR) values and to examine if the adjustment logic (Φ PSII or ETR-based) and crop type influence LED light intensity. The system was tested in a growth chamber with lettuce (Lactuca sativa) 'Green Towers' and cucumber (Cucumis sativus) 'Diva' to maintain six ETR levels (30, 50, 70, 90, 110, 130 μmol·m -2 ·s -1 ) and five Φ PSII levels (0.65, 0.675, 0.7, 0.725, 0.75) during a 16-hour photoperiod. The ETR-based biofeedback quickly stabilized the target ETR within 30-45 minutes, whereas the Φ PSII -based system needed more time. The system adjusted light intensities according to target values, acclimation status, and crop-specific responses. For example, to maintain a target ETR of 130 μmol·m -2 ·s -1 , the gradual increase in Φ PSII over time due to light acclimation allowed the required PPFD to decrease by 35 μmol·m -2 ·s -1 . Lettuce showed higher photosynthetic efficiency and lower heat dissipation than cucumber, leading to higher PPFD adjustments for lettuce. This biofeedback system effectively controls LED light, optimizing photosynthetic efficiency and potentially reducing lighting costs., (© 2025 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Despite being outside of the traditionally defined photosynthetically active radiation (PAR) waveband (400-700 nm), far-red (FR; 700-799 nm) light can increase photosynthesis and induce shade-avoidance responses, which increases light interception and thus, whole-plant growth. However, it is unclear how the promotion of growth from FR light depends on PAR wavebands and specifically how the substitution of red light (600-699 nm) with green light (500-599 nm) influences the efficacy of FR light on increasing shoot biomass accumulation. To determine this, we grew red- and green-leaf lettuce (Lactuca sativa) at a fixed total photon flux density (PFD) with 12 different fractions of red, green, and FR light and the same PFD of blue (400-499 nm) light. We postulated that decreasing the red:FR by substituting FR light for green light, red light, or both would increase shoot fresh mass (FM) until a fraction beyond which growth (but not leaf area) would begin to decrease. Indeed, the substitution of red with FR light increased the leaf area of both cultivars, but FM was greatest under an FR fraction [FR/(R+FR)] of approximately 0.25. Under the greatest FR PFD, FM was similar to lettuce grown without FR light, despite having greater leaf surface area for light interception. Green light had less of an effect on leaf expansion and FM than FR light, and plant diameter and leaf area of red-leaf 'Rouxai' were the greatest when green light fully replaced red light at the highest FR PFD. We conclude that under a modest light intensity and blue PFD, a spectrum that includes up to 25% of far-red photons can increase leaf area and biomass accumulation. While leaf area may continue to increase at higher far-red fractions, fresh mass does not, and plant quality begins to deteriorate., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Kelly, Runkle. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The postharvest lighting environment is a main factor that influences quality preservation for harvested biomass. The objective of this study was to evaluate postharvest changes in bioactive compounds of lettuce with different storage light spectra. The effects of green LEDs with peaks at 500 nm and 530 nm, white LEDs (400-700 nm), and dark storage were evaluated, where light intensity (10 μmol m-2 s-1) and photoperiod (12 h per day) were constant with air temperature at 5°C over the 14 d treatment period. Lettuce stored with 500 nm and 530 nm green LEDs exhibited 1474.5% and 1451.8% (approximately 15.7 and 15.5 times) higher antioxidant activity, respectively, compared to dark storage. Significant improvements in total phenolic content, and 67.5% and 64.8% increases in total soluble solids with 530 nm and 500 nm green LEDs over dark storage were discerned. Exposure to 530 nm green LEDs led to 128.2% (approximately 2.28 times) higher anthocyanin content, a 26.2% increase in carotenoids, and a 95% rise in flavonoid content compared to dark storage. Increases of 26.4% and 16.0% in chlorophyll a content in lettuce stored under 500 nm and 530 nm green LEDs, respectively, and 65.6% and 46.6% rises in the Chlorophyll a/b ratio were observed. Compared to dark storage, green LEDs (500 nm) resulted in a 13.5% higher total chlorophyll content. Findings underscore the positive impact of green LEDs on the nutritional quality of lettuce, providing insight for postharvest practices., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Salehinia et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: Lettuce holds a prominent position in the year-round supply of vegetables, offering a rich array of health-beneficial substances, such as dietary fiber, phenolic compounds, lactucopicrin and lactucin. As such, its flavor has garnered increasing attention. Balancing the enhancement of beneficial compounds with the reduction of undesirable taste is a key focus of scientific research. To investigate short-term management to improve the nutritional quality and flavor of lettuce, combinations of different light intensities (200, 500 and 800 μm ol m -2  s -1 ) and temperatures (10 and 22 °C) were applied separately to 'Lollo Rosso' and 'Little Butter Lettuce' for 7 days before harvest., Results: The results obtained showed that increasing light intensity at low temperatures decreased nitrate content and increased soluble sugar, soluble protein, anthocyanin and phenolic compound content. In the case of lettuce flavor, the bitterness-related metabolites such as lactucin and lactucopicrin were reduced with high light intensity at a low temperature of 10 °C. With this combination, the fructose and glucose contents increased, significantly improving lettuce flavor., Conclusion: Higher light intensity combined with low temperature for 7 days before harvest effectively improved the nutritional quality and flavor of lettuce, suggesting its great potential for use in horticultural practices. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Background: Aquaponic systems are sustainable processes of managing water and nutrients for food production. An innovate nutrient-efficient catfish-based (Clarias gariepinus) aquaponics system was implemented for producing two cultivars of two leafy vegetables largely consumed worldwide: lamb's lettuce (Valerianella locusta var. Favor and Valerianella locusta var. de Hollande) and arugula (Eruca vesicaria var. sativa and Eruca sativa). Different growing treatments (4 × 2 factorial design) were applied to plants of each cultivar, grown at two light intensities (120 and 400 μmol m -2  s -1 ). During growth, several morphological characteristics (root length, plant height, leaf number, foliage diameter and biggest leaf length) were measured. At harvest, plants were weighed and examined qualitatively in terms of greenness and health status. Additionally, leaf extracts were obtained and used to determine total phenolic contents, antioxidant capacities, and levels of cytotoxicity to Caco-2 intestinal model cells., Results: After a 5-week growth period, both lamb's lettuce cultivars presented high levels of greenness and health status, at both light intensities, particularly the var. de Hollande that also showed higher average performance in terms of plant morphology. In turn, arugula cultivars showed lower levels of greenness and health status, especially the cultivar E. vesicaria var. sativa submitted to direct sunlight during growth. In addition, plant specimens submitted to higher levels of light intensity showed higher contents in antioxidants/polyphenols. Cultivars with a higher content in antioxidants/polyphenols led to higher Caco-2 cell viability., Conclusion: For successful industrial implementation of the aquaponics technology, different and optimized acclimatizing conditions must be applied to different plant species and cultivars. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry., (© 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.)

Indoor farming systems enable plant production in precisely controlled environments. However, implementing stable growth conditions and the absence of stress stimulants can weaken plants' defense responses and limit the accumulation of bioactive, health-beneficial phytochemicals. A potential solution is the controlled application of stressors, such as supplemental ultraviolet (UV) light. To this end, we analyzed the efficiency of short-term pre-harvest supplementation of the red-green-blue (RGB, LED) spectrum with ultraviolet B (UV-B) or C (UV-C) light to boost phytochemical synthesis. Additionally, given the biological harm of UV radiation due to high-energy photons, we monitored plants' photosynthetic activity during treatment and their morphology as well as sensory attributes after the treatment. Our analyses showed that UV-B radiation did not negatively impact photosynthetic activity while significantly increasing the overall antioxidant potential of lettuce through enhanced levels of secondary metabolites (total phenolics, flavonoids, anthocyanins), carotenoids, and ascorbic acid. On the contrary, UV-C radiation-induced anthocyanin accumulation in the green leaf cultivar significantly harmed the photosynthetic apparatus and limited plant growth. Taken together, we showed that short-term UV-B light supplementation is an efficient method for lettuce biofortification with healthy phytochemicals, while UV-C treatment is not recommended due to the negative impact on the quality (morphology, sensory properties) of the obtained leafy products. These results are crucial for understanding the potential of UV light supplementation for producing functional plants.

UV can serve as an effective light spectrum for regulating plant secondary metabolites, while relevant studies on UV-A are much less extensive than those on UV-B. A comprehensive understanding of the selective effects of UV-A on different secondary metabolites and the specific features of primary metabolism that drive these effects is still lacking. To address this knowledge gap, we conducted a study to analyze the dynamic changes in the metabolome and transcriptome of lettuce leaves irradiated with red plus UV-A light (monochromatic red light as control). Generally, UV-A promoted the synthesis of most phenylpropanoids and terpenoids originating from the shikimate and methylerythritol phosphate (MEP) pathway in plastids but sacrificed the synthesis of terpenoids derived from the mevalonate (MVA) pathway, particularly sesquiterpenes. Increased precursors supply for the shikimate and MEP pathway under UV-A was directly supported by the activation of the Calvin-Benson cycle and phosphoenolpyruvate transport. Whereas, along with phosphoenolpyruvate transport, the TCA cycle was restrained, causing deprivation of the MVA pathway precursor. In addition, UV-A also activated the plastidic oxidative branch of the pentose phosphate pathway, photorespiration, and malate shuttle, to ensure a sufficient supply of nitrogen, circulation homeostasis of the Calvin-Benson cycle, and energy balance, thus indirectly supporting UV-A-induced specific secondary metabolic output. This study provides a comprehensive framework for understanding the flexible primary-secondary metabolism interactions that are able to produce specific metabolites favorable for adaptation to environmental stimuli.

The visible light spectrum (400-700 nm) powers plant photosynthesis and innumerable other biological processes. Photosynthesis curves plotted by pioneering photobiologists show that amber light (590-620 nm) induces the highest photosynthetic rates in this spectrum. Yet, both red and blue light are viewed superior in their influence over plant growth. Here we report two approaches for quantifying how light wavelength photosynthesis and plant growth using light emitting diodes (LEDs). Resolved quantum yield spectra of tomato and lettuce plants resemble those acquired earlier, showing high quantum utilization efficiencies in the 420-430 nm and 590-620 nm regions. Tomato plants grown under blue (445 nm), amber (595 nm), red (635 nm), and combined red-blue-amber light for 14 days show that amber light yields higher fresh and dry mass, by at least 20%. Principle component analysis shows that amber light has a more pronounced and direct effect on fresh mass, whereas red light has a major effect on dry mass. These data clarify amber light's primary role in photosynthesis and suggest that bandwidth determines plant growth and productivity under sole amber lighting. Findings set precedence for future work aimed at maximizing plant productivity, with widespread implications for controlled environment agriculture., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier B.V. All rights reserved.)

The significant role of aquatic phytoplankton in global primary productivity, accounting for approximately 50 % on an annual basis, has been recognized as a crucial factor in the reduction of Hg(II). In this study, we compared the efficiency of Hg(II) photoreduction mediated by three types of algae leaching dissolved organic matter (DOM) and humic acid (DOM-HA). Especially, we investigated the potential effects of algae-leached DOM on the photoreduction of Hg(II) and its subsequent uptake by lettuce, which serves as an indicator of Hg bioavailability for aquatic plants. The results revealed that under light conditions, the conversion of Hg(II) to Hg(0) mediated by algae-leached DOM and DOM-HA was 6.4-39.9 % higher compared to dark condition. Furthermore, the free radical quenching experiment demonstrated that the reduction of Hg(II) mediated by DOM-HA was higher than algae-leached DOM, mainly due to its ability to generate superoxide anion (O 2 •- ). Moreover, the photoreduction efficiences of Hg(II) mediated by algae-leached DOM were 29-18 % lower compared to DOM-HA. The FT-IR analysis revealed that the production of -SH from algae-leached DOM led to the formation of strong metal-complexes, which restricts the reduction process from Hg(II) to Hg(0). Finally, the hydroponics experiment demonstrated that algae-leached DOM inhibited the bioavailability of Hg(II) to plants more effectively than DOM-HA. Our research emphasizes the significant functional roles and potential mechanisms of algae in reducing Hg levels, thereby influencing the availability of Hg in aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2024. Published by Elsevier B.V.)

Ultrasound technology has been focused on due to its unique advantages in biofilm removal compared with traditional antibacterial methods. Herein, the anti-biofilm properties of low-frequency ultrasound (LFUS) were studied against Enterohemorrhagic Escherichia coli O157: H7 (E. coli O157:H7). After ultrasonication (20 kHz, 300 W) for 5 min, the removal rate of biofilm from polystyrene sheets reached up to 99.999 %. However, the bacterial cells could not be inactivated completely even extending the duration of ultrasonic irradiation to 30 min. Fortunately, this study indicated that LFUS could efficiently weaken the metabolic capacity and biofilm-forming ability of bacterial cells separated from biofilm. It could be associated with the removal of cell surface appendages and damage to cell membrane induced by mechanical vibration and acoustic cavitation. Besides, the genetic analysis proved that the transcription level of genes involved in curli formation was significantly down-regulated during ultrasonic irradiation, thus impeding the process of irreversible adhesion and cells aggregation. Finally, the actual application effect of LFUS was also evaluated in different fresh produces model. The results of this study would provide a theoretical basis for the further application of ultrasound in the food preservation., Competing Interests: Declaration of competing interest No conflict of interest exists in the submission of this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Lettuce (Lactuca sativa L.) cultivated in facilities display low vitamin C (L-ascorbic acid (AsA)) contents which require augmentation. Although UV-B irradiation increases the accumulation of AsA in crops, processes underlying the biosynthesis as well as metabolism of AsA induced by UV-B in lettuce remain unclear., Results: UV-B treatment increased the AsA content in lettuce, compared with that in the untreated control. UV-B treatment significantly increased AsA accumulation in a dose-dependent manner up until a certain dose.. Based on optimization experiments, three UV-B dose treatments, no UV-B (C), medium dose 7.2 KJ·m - 2 ·d - 1 (U1), and high dose 12.96 KJ·m - 2 ·d - 1 (U2), were selected for transcriptome sequencing (RNA-Seq) in this study. The results showed that C and U1 clustered in one category while U2 clustered in another, suggesting that the effect exerted on AsA by UV-B was dose dependent. MIOX gene in the myo-inositol pathway and APX gene in the recycling pathway in U2 were significantly different from the other two treatments, which was consistent with AsA changes seen in the three treatments, indicating that AsA accumulation caused by UV-B may be associated with these two genes in lettuce. UVR8 and HY5 were not significantly different expressed under UV-B irradiation, however, the genes involved in plant growth hormones and defence hormones significantly decreased and increased in U2, respectively, suggesting that high UV-B dose may regulate photomorphogenesis and response to stress via hormone regulatory pathways, although such regulation was independent of the UVR8 pathway., Conclusions: Our results demonstrated that studying the application of UV-B irradiation may enhance our understanding of the response of plant growth and AsA metabolism-related genes to UV-B stress, with particular reference to lettuce., (© 2023. The Author(s).)

Key Message: A population of lettuce that segregated for photoperiod sensitivity was planted under long-day and short-day conditions. Genetic mapping revealed two distinct sets of QTLs controlling daylength-independent and photoperiod-sensitive flowering time. The molecular mechanism of flowering time regulation in lettuce is of interest to both geneticists and breeders because of the extensive impact of this trait on agricultural production. Lettuce is a facultative long-day plant which changes in flowering time in response to photoperiod. Variations exist in both flowering time and the degree of photoperiod sensitivity among accessions of wild (Lactuca serriola) and cultivated (L. sativa) lettuce. An F 6 population of 236 recombinant inbred lines (RILs) was previously developed from a cross between a late-flowering, photoperiod-sensitive L. serriola accession and an early-flowering, photoperiod-insensitive L. sativa accession. This population was planted under long-day (LD) and short-day (SD) conditions in a total of four field and screenhouse trials; the developmental phenotype was scored weekly in each trial. Using genotyping-by-sequencing (GBS) data of the RILs, quantitative trait loci (QTL) mapping revealed five flowering time QTLs that together explained more than 20% of the variation in flowering time under LD conditions. Using two independent statistical models to extract the photoperiod sensitivity phenotype from the LD and SD flowering time data, we identified an additional five QTLs that together explained more than 30% of the variation in photoperiod sensitivity in the population. Orthology and sequence analysis of genes within the nine QTLs revealed potential functional equivalents in the lettuce genome to the key regulators of flowering time and photoperiodism, FD and CONSTANS, respectively, in Arabidopsis., (© 2021. The Author(s).)

Lettuce is commonly consumed around the world, spurring the cultivation of green- and red-leaf varieties in indoor farms. One common consideration for indoor cultivation is the light wavelengths/spectrum, which is an important factor for regulating growth, development, and the accumulation of metabolites. Here, we show that Batavia lettuce (Lactuca sativa cv. "Batavia") grown under a combination of red (R) and blue (B) light (RB, R:B = 3:1) displayed better growth and accumulated more anthocyanin than lettuce grown under fluorescent light (FL). Anthocyanin concentration was also higher in mature stage than early stage lettuce. By performing a comparative transcriptome analysis of early and mature stage lettuce grown under RB or FL (RB or FL-lettuce), we found that RB induced the expression of genes related to oxidation-reduction reaction and secondary metabolite biosynthesis. Furthermore, plant age affected the transcriptome response to RB, as mature RB-lettuce had six times more differentially expressed genes than early RB-lettuce. Also, genes related to the accumulation of secondary metabolites such as flavonoids and anthocyanins were more induced in mature RB-lettuce. A detailed analysis of the anthocyanin biosynthesis pathway revealed key genes that were up-regulated in mature RB-lettuce. Concurrently, branching pathways for flavonol and lignin precursors were down-regulated., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This study investigated the individual and combined effects of ultraviolet A (UV-A) and far-red (FR) light irradiation on the biomass, phytochemical accumulation, and antioxidant capacity of two lettuce cultivars in an artificial light plant factory. UV-A supplementation yielded a smaller leaf area and reduced biomass and nitrate content. In contrast, it improved the chlorophyll, soluble protein, soluble sugar, vitamin C, flavonoid, polyphenol, and anthocyanin contents and the 2,2-diphenyl-1-picrylhydrazyl radical-scavenging rate. FR irradiation resulted in a larger leaf area, whereas the lettuce biomass remained unchanged. Irradiation with both UV-A and FR light exhibited the most remarkable effect on leaf expansion and biomass, but reduced the phytochemical contents. A significant interaction between the cultivar and supplemented light was observed for most plant parameters., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Heat shock factors (Hsfs) and Heat shock proteins (Hsps) belong to an essential group of molecular regulators involved in controlling cellular processes under normal and stress conditions. The role of Hsfs and Hsps is well known in model plant species under diverse stress conditions. While plants Hsfs are vital components of the signal transduction response to maintain cellular homeostasis, Hsps function as chaperones helping to maintain folding of damaged and newly formed proteins during stress conditions. In lettuce (Lactuca sativa), a highly consumed vegetable crop grown in the field and in hydroponic systems, the role of these gene families in response to artificial light is not well characterized., Results: Using a genome-wide analysis approach, we identified 32 Hsfs and 22 small heat shock proteins (LsHsps) in lettuce, some of which do not have orthologs in Arabidopsis, poplar, and rice. LsHsp60s, LsHsp90s, and LsHsp100s are highly conserved among dicot and monocot species. Surprisingly, LsHsp70s have three times more members than Arabidopsis and two times more than rice. Interestingly, the lettuce genome triplication did not contribute to the increased number of LsHsp70s genes. The large number of LsHsp70s was the result of genome tandem duplication. Chromosomal distribution analysis shows larger tandem repeats of LsHsp70s genes in Chr1, Chr7, Chr8, and Chr9. At the transcriptional level, some genes of the LsHsfs, LsHsps, LsHsp60s, and LsHsp70s families were highly responsive to UV and high intensity light stress, in contrast to LsHsp90s and LsHsp100s which did not respond to a light stimulus., Conclusions: Our genome-wide analysis provides a detailed identification of Hsfs and Hsps in lettuce. Chromosomal location and syntenic region analysis together with our transcriptional analysis under different light conditions provide candidate genes for breeding programs aiming to produce lettuce varieties able to grow healthy under hydroponic systems that use artificial light.

Radio frequency (RF) is an emerging technology applied in blanching treatment as alternative to conventional treatment. This study aimed to investigate the effects of RF heating rate on peroxidase (POD) inactivating efficiency, physiochemical properties (texture, color and vitamin C) and cell structure of stem lettuce. POD enzyme inactivation efficiency increased with increased RF heating rate. When POD activity was reduced to <5%, better physiochemical properties and less cell damage occurred in RF heating compared with conventional hot water (HW) blanching (HWB); Relative electrolyte leakage (REL) analysis and microscopic observation suggested that the loss of integrity of cell walls and membranes, the decrease in turgor pressure and the weakened connections between adjacent cells leaded to the deterioration of physiochemical properties. The degrees of cell destruction varied with RF heating rates, which provide a new idea for RF blanching for producing different types of fruits and vegetables products (Solid and juice products)., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Bioregenerative life-support systems (BLSS) involving plants will be required to realize self-sustaining human settlements beyond Earth. To improve plant productivity in BLSS, the quality of the solar spectrum can be modified by lightweight, luminescent films. CuInS 2 /ZnS quantum dot (QD) films were used to down-convert ultraviolet/blue photons to red emissions centered at 600 and 660 nm, resulting in increased biomass accumulation in red romaine lettuce. All plant growth parameters, except for spectral quality, were uniform across three production environments. Lettuce grown under the 600 and 660 nm-emitting QD films respectively increased edible dry mass (13 and 9%), edible fresh mass (11% each), and total leaf area (8 and 13%) compared with under a control film containing no QDs. Spectral modifications by the luminescent QD films improved photosynthetic efficiency in lettuce and could enhance productivity in greenhouses on Earth, or in space where, further conversion is expected from greater availability of ultraviolet photons.

Sub-optimal growing conditions have a major effect on plants; therefore, large efforts are devoted to maximizing the availability of agricultural inputs to crops. To increase the sustainable use of non-renewable inputs, attention is currently given to the study of plants under non-optimal conditions. In this work, we investigated the impact of sub-optimal macrocations availability and light intensity in two lettuce varieties that differ for the accumulation of secondary metabolites (i.e., 'Red Salanova' and 'Green Salanova'). Photosynthesis-related measurements and untargeted metabolomics were used to identify responses and pathways involved in stress resilience. The pigmented ('Red') and the non-pigmented ('Green Salanova') lettuce exhibited distinctive responses to sub-optimal conditions. The cultivar specific metabolomic signatures comprised a broad modulation of metabolism, including secondary metabolites, phytohormones, and membrane lipids signaling cascade. Several stress-related metabolites were altered by either treatment, including polyamines (and other nitrogen-containing compounds), phenylpropanoids, and lipids. The metabolomics and physiological response to macrocations availability and light intensity also implies that the effects of low-input sustainable farming systems should be evaluated considering a range of cultivar-specific positive and disadvantageous metabolic effects in addition to yield and other socio-economic parameters.

This paper investigated the effects of radio-frequency (RF) energy and conventional hot-water blanching (95 °C for 2 min) on the peroxidase (POD) activity, physiochemical properties, and changes in the cellular morphology of stem lettuce. The relative residual POD activity significantly decreased (P < 0.05) from 66.03% to 6.46% with increased RF heating temperature (65 °C-85 °C). The weight loss (3.06%-7.64%), color, texture, relative electrolyte leakage (23.45%-67.90%), and residual vitamin C content (72.22%-16.67%) significantly changed (P < 0.05) with increased RF heating temperature (65 °C-85 °C). Micrographs indicated that the changes in physiochemical property can be attributed to the destruction of cell membranes, loss of cell turgor, reduced rigidity of cell walls, and loose adhesion between adjacent cells. Samples treated by RF heating at 75 °C showed lesser cell damage and better nutrient retention than those treated by hot-water blanching at a similar level of POD inactivation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This research aimed to investigate the effects of three LED spectra on growth, gas exchange, antioxidant activity and nutritional quality of three vegetable species. The compressible vegetable facilities (CVF) were developed and three kinds of typical LED lights (spectra) were set, including white LED light (W), red-blue-green LED light (RBG), and red-blue-white LED light (RBW). Three vegetable species, i.e. lettuce (Lactuca sativa L. cv. Rome), cherry radish (Raphanus sativas L. cv. Hongxin) and cherry tomato (Lycopersicon esculentum M. cv. Mosite), were chosen and grown (matrix culture) in the three LED lights for 40, 40 and 100 days, respectively. The results indicated that the vegetable plants grew well and were compact in the RBG and RBW treatments. There was the highest biomass or fruit (tomato) in the RBG treatment and the least one in the W treatment for three vegetable species. There were no significant differences in harvest index, ratio of shoot to root, and water content among three treatments. The production efficiency values of 9.0-9.7, 9.9-13.5 and 11.8-12.5 g DW d -1 m -2 for lettuce, radish and tomato plants in the RBG and the RBW treatments were higher than those in the W treatment. The photosynthetic and transpiration rates of three vegetable species in the RBG treatment were the highest among three treatments and the W treatment had the least one. There were significant effects of three spectra on antioxidant activities of three vegetable species. Higher PPFD percentages of blue in the RBG light and the RBW light increased the antioxidant activities of all vegetable plants compared the W light. But it had no significant difference between the RBG light and the RBW. The organic components including soluble sugar (SS) and protein (Prt) of lettuce and radish plants were affected significantly by three spectra, but not for tomato plants. The contents of Mg and Zn of radish plants in the RBG treatment were higher than those in other treatments. There were significant positive effects of RBW treatment on the contents of N and Mg of tomato plants. The different spectra did not affect the contents of N-NO 3 and Cu of vegetable plants. This study demonstrated that the RBG light (spectrum) significantly enhanced the growth, gas exchange, antioxidant activity of the lettuce, radish, and tomato cultivars used in this study, and there are significant effects of different LED spectra on the nutritional quality (including organic components and several mineral elements) of the different species., Competing Interests: Declaration of Competing Interest All authors have submitted the Conflict of Interest Checklist disclosure form and declare that: (i) no support, financial or otherwise, has been received from any organization that may have an interest in the submitted work; and (ii) there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2020 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.)

Leaves of lettuce, pepper, tomato and grapevine plants grown in greenhouse conditions were exposed to UV-C light for either 60 s or 1 s, using a specific LEDs-based device, and wavelengths and energy were the same among different light treatments. Doses of UV-C light that both effectively stimulated plant defences and were innocuous were determined beforehand. Tomato plants and lettuce plants were inoculated with Botrytis cinerea, pepper plants with Phytophthora capsici, and grapevine with Plasmopara viticola. In some experiments we investigated the effect of a repetition of treatments over periods of several days. All plants were inoculated 48 h after exposure to the last UV-C treatment. Lesions on surfaces were measured up to 12 days after inoculation, depending on the experiment and the pathogen. The results confirmed that UV-C light stimulates plant resistance; they show that irradiation for one second is more effective than irradiation for 60 s, and that repetition of treatments is more effective than single light treatments. Moreover a systemic effect was observed in unexposed leaves that were close to exposed leaves. The mechanisms of perception and of the signalling and metabolic pathways triggered by flashes of UV-C light vs. 60 s irradiation exposures are briefly discussed, as well as the prospects for field use of UV-C flashes in viticulture and horticulture., Competing Interests: The authors have declared that no competing interests exist.

Light and nutrient are important factors for vegetable production in plant factory or greenhouse. The total 12 treatments which contained the combination of four light intensity (150, 250, 350 and 450 μmol · m -2  · s -1 ) and three nutrient solution concentration (NSC) (1/4, 1/2, 3/4 strength NSC) were established for investigation of lettuce growth and quality in a growth chamber. The combination of light intensity and NSC exhibited significant effects on photosynthetic pigment, nutritional quality, mineral content and antioxidant capacity. That a higher light intensity were readily accessible to higher chlorophyll a/b showed in lettuce of treatment of 350 μmol · m -2  · s -1  × 3/4NSC and 450 μmol · m -2  · s -1  × 1/4NSC. Lower total N contents, higher content of soluble protein, vitamin C, soluble sugar and free amino acid exhibited in lettuce under treatment of 250 and 350 μmol · m -2  · s -1  × 1/4NSC or 3/4NSC. With increasing NSC and LED irradiance, the content of total P and K in lettuce increased and decreased, respectively. The highest and lowest total Ca content were found in treatment of 150 μmol · m -2  · s -1  × 1/4NSC and 450 μmol · m -2  · s -1  × 1/4NSC, respectively, and higher content of total Mg and Zn was observed under 250 μmol m -2 s -1  × 1/4NSC and 150 μmol · m -2  · s -1  × 3/4NSC, respectively. The antioxidant contents generally decreased with increasing NSC level. The higher antioxidant content and capacity occurred in lettuce of 350 μmol · m -2  · s -1  × 1/4NSC treatment. The interaction of 350 μmol · m -2  · s -1  × 1/4NSC might be the optimal condition for lettuce growth in plant factory.

The objective of the study was to investigate the effects of growth-stage specific lighting for the physiological homeostasis of red leaf lettuce (Lactuca sativa L. cv. Red Cos), by measuring the productivity of photosynthesis and primary metabolism. In the experiments, the main photosynthetic photon flux consisted of red (R) and blue (B) light, supplemented with blue, green (G) or UV-A wavelengths. Decrease of fructose, accompanied by significant decrease of stomatal conductance (gs), the ratio of intracellular to ambient CO 2 concentration (C i /C a ), photosynthetic rate (Pr), light adapted actual quantum yield of PSII photochemistry (Φ PSII ), biomass formation and significant increase of transpiration rate (Tr) suggest that supplemental UV-A during maturity stage, after supplemental green irradiation during seedling stage (BRG to BRUV) was the least favourable condition for red leaf lettuce. However, constant irradiation with supplemental green (BRG) or supplemental green irradiation after increased blue exposure (B ↑ R to BRG) resulted in significant increase of Pr, gs, Ci/Ca, and light use efficiency(LUE), and decrease of Tr and Water use efficiency (WUE). Significant increase of leaf area was observed under supplemental green in both seedlings (BR; BRG) and matured plants (B ↑ R to BRG). Significant increase of specific leaf area was found under supplemental green (BRG) for seedlings and under increased blue (B ↑ R) for matured plants. Accordingly, the most favourable growth-stage specific lighting spectrum strategy for red leaf lettuce, based on photosynthetic and primary metabolite response, is supplemental green irradiation after increased blue exposure (B ↑ R to BRG), whereas, the most favourable condition for seedlings is BRG. According to the PCA correlation matrix, associations among the measured data indicate that WUE negatively correlated with gs and C i /C a , while LUE positively correlated with gs and Pr. However, weak correlations between Ф PSII , LUE and photochemical reflectance index (PRI) suggest that selected light conditions were not optimal for red leaf lettuce., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Understanding plant responses to light quantity in indoor horticultural systems is important for optimising lettuce growth and metabolism as well as energy utilisation efficiency. Light intensity and photoperiod sufficient for normal plant growth parameters might be not efficient for nitrate assimilation. Therefore, this study explored and compared the effects of different light intensities (100-500 μmol m -2 s -1 ) and photoperiods (12-24 h) on the growth and nitrate assimilation in red and green leaf lettuce (Lactuca sativa L.)., Results: For efficient nitrate assimilation, 300-400 μmol m -2 s -1 photosynthetic photon flux density (PPFD) and 16-18 h photoperiod is necessary for red and green lettuces. The insufficient light quantity resulted in reduced growth and remarkable increase in nitrate and nitrite contents in both cultivars. Short photoperiods, similarly to low PPFD, growth parameters, chlorophyll indices and nitrate assimilation indices showed the shortage of photosynthetic products for normal plant physiological processes. Short photoperiods had the least pronounced effect on nitrate and nitrite contents in lettuce leaves., Conclusion: Light intensity was superior compared to photoperiods for efficient nitrate assimilation in both lettuce cultivars. Under short photoperiods, similarly to low intensity, growth parameters, chlorophyll index and nitrate assimilation indices showed a shortage of photosynthetic products for normal physiological processes. The free amino acid concentration increased, but it was not efficiently incorporated in proteins, as their level in lettuce was lower compared to those for moderate photoperiods. © 2019 Society of Chemical Industry., (© 2019 Society of Chemical Industry.)

Light-converting polypropylene spunbond was first used in the study of the key physiological parameters of plants. A comparative study of the functioning of the photosynthetic apparatus and the dynamics of growth in late cabbage plants (Olga variety) and leaf lettuce (Emerald variety) was conducted using the ordinary nonwoven polypropylene fabric (spunbond) (density 30 g·m -2 ) and the spunbond containing a photoluminophore (PL) (1.6% yttrium oxysulfide doped with europium). The plants were grown in a glass greenhouse without spunbond and under the spunbond containing and not containing the PL that transforms a part of UV-radiation into red light radiation. The use of the spunbond led to a decrease in the rate of photosynthesis, activity of the photosystem 2, and the accumulation of plant biomass and to an increase in the stomatal conductance. By contrast to unmodified spunbond, the application of the spunbond containing the PL led to an increase in the rate of photosynthesis, the water-use efficiency (WUE), and the accumulation of the total biomass of plants by 30-50% but to a decrease in the transpiration rate and the stomatal conductance. It is assumed that the positive effect of the PL is associated with an increase in the fraction of fluorescent red light, which enhances photosynthetic activity and accelerates plant growth.

One (1P), two (2P), three (3P) or four (4P) pulses of light supplied by a xenon lamp, were applied to young lettuce plants grown in pots. The lamp used in the trial was similar to those used for fruit surface sterilization. Total flavonols were measured in leaves using the Dualex method. In a first trial conducted in greenhouse conditions, 6 days after the pulsed light (PL) treatment, flavonols were increased by 312% and 525% in the 3P and 4P treatments, respectively, in comparison to the those in the untreated control. Changes in the chlorophyll fluorescence parameters suggest that the PL treatment may induce limited and transient damage to the photosynthetic machinery and that the damage increases with the increasing number of pulses. The performance parameters were not significantly affected by PL and recovered fully by 6 days after the treatments. The 1P and the 2P treatments 6 days after the treatment showed a 28.6% and a 32.5% increase, respectively, in net photosynthetic assimilation, when compared to that of the control. However, 8 days after the treatment, there was no longer a difference between the treatments and the control in net photosynthetic assimilation. Eight days after the light treatment, the 3P treatment showed a 38.4% increase in maximal net photosynthetic assimilation over that of the control, which is an indication of positive long-term adaptation of photosynthetic capacity. As a whole, our observations suggest that PL could be used on field or greenhouse crops to increase their phytochemical content. No long-lasting or strong negative effects on photosynthesis were associated with PL within the range of doses we tested; some observations even suggest that certain treatments could result in an additional positive effect. This conclusion is supported by a second trial conducted in phytotrons. More studies are required to better understand the roles of the different wavelengths supplied by PL and their interactions., Competing Interests: NOVAGENETIC provided supported in the form of salaries for author (Salah Fgaier), but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Linear electron transport depends on balanced excitation of photosystem I and II. Far-red light preferentially excites photosystem I (PSI) and can enhance the photosynthetic efficiency when combined with light that over-excites photosystem II (PSII). The efficiency of different wavelengths of far-red light exciting PSI was quantified by measuring the change in quantum yield of PSII (Φ PSII ) of lettuce (Lactuca sativa) under red/blue light with narrowband far-red light added (from 678 to 752 nm, obtained using laser diodes). The Φ PSII of lettuce increased with increasing wavelengths of added light from 678 to 703 nm, indicating longer wavelengths within this region are increasingly used more efficiently by PSI than by PSII. Adding 721 nm light resulted in similar Φ PSII as adding 703 nm light, but Φ PSII tended to decrease as wavelength increased from 721 to 731 nm, likely due to decreasing absorptance and low photon energy. Adding 752 nm light did not affect Φ PSII . Leaf chlorophyll fluorescence light response measurements showed lettuce had higher Φ PSII under halogen light (rich in far-red) than under red/blue light (which over-excites PSII). Far-red light is more photosynthetically active than commonly believed, because of its synergistic interaction with light of shorter wavelengths., (© 2018 Scandinavian Plant Physiology Society.)

Insights into the environmental fates of nitrated polycyclic aromatic hydrocarbons (NPAHs) in edible vegetables are of great significance for better evaluating human exposure to NPAHs through the dietary pathway. In this work, a fluorescence quenching method using graphene quantum dots as a fluorescent probe was first applied for the in vivo determination of 9-nitroanthracene (9-NAnt) and 1-nitropyrene (1-NPyr) adsorbed on the leaf surfaces of living lettuce ( Lactuca sativa L.) seedlings. Moreover, the photolysis kinetics and mechanisms of the two adsorbed NPAHs were discussed. The photodegradation kinetics followed the pseudo-first-order equation, and the photodegradation half-life of 1-NPyr (7.4 ± 0.2 h) was greater than that of 9-NAnt (2.3 ± 0.1 h). Anthraquinone and pyrenediones were identified to be the main photolytic products of 9-NAnt and 1-NPyr, respectively. Intramolecular rearrangement was the most reasonable mechanism for the NPAH photolysis. The photolysis-driven degradation exhibited a key role in scavenging NPAHs from the vegetable leaf, indicating the reduction of NPAH transportation in the food chain.

The present study evaluated the growth response and sugar accumulation of lettuce exposed to different lighting modes of red and blue LED light based on the same daily light integral (7.49 μmol·m -2 ). Six lighting treatments were performed, that were monochromatic red light (R), monochromatic blue light (B), simultaneous red and blue light as the control (RB, R:B = 1:1), mixed modes of R, B and RB (R/RB/B, 4 h R to 4 h RB and then 4 h B), and alternating red and blue light with alternating intervals of 4 h and 1 h respectively recorded as R/B(4 h) and R/B(1 h). The Results showed that different irradiation modes led to obvious morphological changes in lettuce. Among all the treatments, the highest fresh and dry weight of lettuce shoot were both detected with R/B(1 h), significantly higher than the other treatments. Compared with plants treated with RB, the contents of fructose, glucose, crude fiber as well as the total sweetness index (TSI) of lettuce were significantly enhanced by R treatment; meanwhile, monochromatic R significantly promoted the activities of sucrose degrading enzymes such as acid invertase (AI) and neutral invertase (NI), while obviously reduced the activity of sucrose synthesizing enzyme (SPS). Additionally. The highest contents of sucrose and starch accompanied with the strongest activity of SPS were detected in plants treated with R/B(1 h). The alternating treatments R/B(4 h) and R/B(1 h) inhibited the activity of SS, while enhanced that of SPS compared with the other treatments, indicating that different light environment might influence sugar compositions via regulating the activities of sucrose metabolism enzymes. On the whole, R/B(1 h) was the optimal lighting strategy in terms of lettuce yield, taste and energy use efficiency in the present study.

Enhancement of the diffuse solar radiation to which lettuce plants were exposed clearly affected the vitamin C content and the quantitative and qualitative patterns of phenolic compounds and free amino acids (AA) in the leaves. Although the enhanced level of diffuse light was detrimental to the contents of vitamin C and total phenolic compounds, lowering them by 10-46% and 8-11%, respectively, the content of di-caffeoyltartaric acid increased from 0.26 ± 0.19 to 0.52 ± 0.10 μmol 100 g -1  f.w. for plants harvested in summer. The effect of diffuse light on AA depended on the total amount of global radiation incident on the plants. Considering the lowest amount of global radiation, the enhanced diffuse light increased the AA content from 766 ± 89 to 849 ± 90 μmol 100 g -1  f.w. By contrast, under the highest level of global radiation, diffuse light decreased the amount of AA from 990 ± 16 to 830 ± 76 μmol 100 g -1  f.w., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

To optimize crop production/quality in space, we studied various "light recipes" that could be used in the Advanced Plant Habitat currently aboard the International Space Station (ISS). Lettuce (Lactuca sativa cv. 'Outredgeous') plants were grown for 28 days under seven treatments of white (W) LEDs (control), red (635 nm) and blue (460 nm) (RB) LEDs, W + blue (B) LEDs, W + green (520 nm) (G) LEDs, W + red (R) LEDs, W + far red (745 nm) (FR) LEDs, and RGB + FR LEDs with ratios similar to natural sunlight. Total PAR was maintained near 180 µmol m -2  s -1 with an 18 h photoperiod. Lettuce grown under RGB + FR produced the greatest leaf expansion and overall shoot biomass, while leaves from WB and RB showed the highest levels of pigmentation, secondary metabolites, and elemental nutrients. All other supplemental treatments had varying impacts on morphology that were dependent on crop age. The WG treatment increased fresh mass early in the cycle, while WR increased biomass later in the cycle. The plants grown under WFR exhibited elongation of petioles, lower nutrient content, and similar shoot biomass to the W control. The findings suggest that supplementing a broad spectrum, white light background with discrete wavelengths can be used to manipulate total yield, morphology, and levels of phytonutrients in lettuce at various times during the crop cycle., (Copyright © 2018. Published by Elsevier Ltd.)

Red and blue light are the most important light spectra for driving photosynthesis to produce adequate crop yield. It is also believed that green light may contribute to adaptations to growth. However, the effects of green light, which can trigger specific and necessary responses of plant growth, have been underestimated in the past. In this study, lettuce (Lactuca sativa L.) was exposed to different continuous light (CL) conditions for 48 h by a combination of red and blue light-emitting diodes (LEDs) supplemented with or without green LEDs, in an environmental-controlled growth chamber. Green light supplementation enhanced photosynthetic capacity by increasing net photosynthetic rates, maximal photochemical efficiency, electron transport for carbon fixation (J PSII ) and chlorophyll content in plants under the CL treatment. Green light decreased malondialdehyde and H 2 O 2 accumulation by increasing the activities of superoxide dismutase (EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) after 24 h of CL. Supplemental green light significantly increased the expression of photosynthetic genes LHCb and PsbA from 6 to 12 h, and these gene expressions were maintained at higher levels than those under other light conditions between 12 and 24 h. However, a notable downregulation of both LHCb and PsbA was observed during 24 to 48 h. These results indicate that the effects of green light on lettuce plant growth, via enhancing activity of particular components of antioxidative enzyme system and promoting of LHCb and PsbA expression to maintain higher photosynthetic capacity, alleviated a number of the negative effects caused by CL., (© 2018 Scandinavian Plant Physiology Society.)

Square-wave pulsed light is characterized by three parameters, namely average photosynthetic photon flux density (PPFD), pulsed-light frequency, and duty ratio (the ratio of light-period duration to that of the light-dark cycle). In addition, the light-period PPFD is determined by the averaged PPFD and duty ratio. We investigated the effects of these parameters and their interactions on net photosynthetic rate (P n ) of cos lettuce leaves for every combination of parameters. Averaged PPFD values were 0-500 µmol m -2  s -1 . Frequency values were 0.1-1000 Hz. White LED arrays were used as the light source. Every parameter affected P n and interactions between parameters were observed for all combinations. The P n under pulsed light was lower than that measured under continuous light of the same averaged PPFD, and this difference was enhanced with decreasing frequency and increasing light-period PPFD. A mechanistic model was constructed to estimate the amount of stored photosynthetic intermediates over time under pulsed light. The results indicated that all effects of parameters and their interactions on P n were explainable by consideration of the dynamics of accumulation and consumption of photosynthetic intermediates.

Light-emitting diodes (LEDs) are an artificial light source used in closed-type plant factories and provide a promising solution for a year-round supply of green leafy vegetables, such as lettuce (Lactuca sativa L.). Obtaining high-quality seedlings using controlled irradiation from LEDs is critical, as the seedling health affects the growth and yield of leaf lettuce after transplantation. Because key molecular pathways underlying plant responses to a specific light quality and intensity remain poorly characterised, we used a multi-omics-based approach to evaluate the metabolic and transcriptional reprogramming of leaf lettuce seedlings grown under narrow-band LED lighting. Four types of monochromatic LEDs (one blue, two green and one red) and white fluorescent light (control) were used at low and high intensities (100 and 300 μmol·m -2 ·s -1 , respectively). Multi-platform mass spectrometry-based metabolomics and RNA-Seq were used to determine changes in the metabolome and transcriptome of lettuce plants in response to different light qualities and intensities. Metabolic pathway analysis revealed distinct regulatory mechanisms involved in flavonoid and phenylpropanoid biosynthetic pathways under blue and green wavelengths. Taken together, these data suggest that the energy transmitted by green light is effective in creating a balance between biomass production and the production of secondary metabolites involved in plant defence.

Main Conclusion: Environmentally induced variation and the genotypic differences in flavonoid and phenolic content in lettuce can be reliably detected using the appropriate parameters derived from the records of rapid non-invasive fluorescence technique. The chlorophyll fluorescence excitation ratio method was designed as a rapid and non-invasive tool to estimate the content of UV-absorbing phenolic compounds in plants. Using this technique, we have assessed the dynamics of accumulation of flavonoids related to developmental changes and environmental effects. Moreover, we have tested appropriateness of the method to identify the genotypic differences and fluctuations in total phenolics and flavonoid content in lettuce. Six green and two red genotypes of lettuce (Lactuca sativa L.) grown in pots were exposed to two different environments for 50 days: direct sunlight (UV-exposed) and greenhouse conditions (low UV). The indices based on the measurements of chlorophyll fluorescence after red, green and UV excitation indicated increase of the content of UV-absorbing compounds and anthocyanins in the epidermis of lettuce leaves. In similar, the biochemical analyses performed at the end of the experiment confirmed significantly higher total phenolic and flavonoid content in lettuce plants exposed to direct sun compared to greenhouse conditions and in red compared to green genotypes. As the correlation between the standard fluorescence indices and the biochemical records was negatively influenced by the presence of red genotypes, we proposed the use of a new parameter named Modified Flavonoid Index (MFI) taking into an account both absorbance changes due to flavonol and anthocyanin content, for which the correlation with flavonoid and phenolic content was relatively good. Thus, our results confirmed that the fluorescence excitation ratio method is useful for identifying the major differences in phenolic and flavonoid content in lettuce plants and it can be used for high-throughput pre-screening and phenotyping of leafy vegetables in research and breeding applications towards improvement of vegetable health effects.

Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve "color rendering" of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 μmol·m -2 ·s -1 for a 16 hd -1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the "color rendering" of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2-3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth.

The purpose of the present study was to evaluate the role of proline (Pro) in relieving UV-B radiation-induced oxidative stress in lettuce. Lettuce seedlings were exposed to 3.3 W m -2 UV-B radiation for 12 h after pre-treatment sprayed with 20 mM Pro. The data for malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ), endogenous Pro level, the activities of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD)], total phenolic concentration, antioxidant capacity, expression of phenylalanine ammonia lyase (PAL), γ-tocopherol methyltransferase (γ-TMT) and proline dehydrogenase (ProDH) genes, phytohormone levels such as abscisic acid (ABA), gibberellic acid (GA), indole acetic acid (IAA) and salicylic acid (SA), soluble sugars and organic acids were recorded. It was found that Pro alleviated the oxidative damage in the seedlings of lettuce as demonstrated by lower lipid peroxidation and H 2 O 2 content, increasing the endogenous Pro level, the activity of antioxidant enzymes, total phenolic concentration and the antioxidant capacity. Additionally, it was revealed that exogenous application of Pro enhanced the levels of GA, IAA, the concentrations of soluble sugars and organic acids and expressions of PAL, γ-TMT and ProDH genes as compared to the control. The results obtained in this study suggest that pre-treatment with exogenous Pro provides important contributions to the increase in the UV-B tolerance of lettuce by regulating the biochemical mechanisms of UV-B response.

The efficiency of monochromatic light to drive photosynthesis drops rapidly at wavelengths longer than 685nm. The photosynthetic efficiency of these longer wavelengths can be improved by adding shorter wavelength light, a phenomenon known as the Emerson enhancement effect. The reverse effect, the enhancement of photosynthesis under shorter wavelength light by longer wavelengths, however, has not been well studied and is often thought to be insignificant. We quantified the effect of adding far-red light (peak at 735nm) to red/blue or warm-white light on the photosynthetic efficiency of lettuce (Lactuca sativa). Adding far-red light immediately increased quantum yield of photosystem II (Φ PSII ) of lettuce by an average of 6.5 and 3.6% under red/blue and warm-white light, respectively. Similar or greater increases in Φ PSII were observed after 20min of exposure to far-red light. This longer-term effect of far-red light on Φ PSII was accompanied by a reduction in non-photochemical quenching of fluorescence (NPQ), indicating that far-red light reduced the dissipation of absorbed light as heat. The increase in Φ PSII and complementary decrease in NPQ is presumably due to preferential excitation of photosystem I (PSI) by far-red light, which leads to faster re-oxidization of the plastoquinone pool. This facilitates reopening of PSII reaction centers, enabling them to use absorbed photons more efficiently. The increase in Φ PSII by far-red light was associated with an increase in net photosynthesis (P n ). The stimulatory effect of far-red light increased asymptotically with increasing amounts of far-red. Overall, our results show that far-red light can increase the photosynthetic efficiency of shorter wavelength light that over-excites PSII., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Dittrichia viscosa (L.) W. Greuter is a pioneer species belonging to the Compositae family. It is widespread in the Mediterranean basin, where it is considered invasive. It is a source of secondary metabolites, playing an important ecological role. D. viscosa plant extracts showed a phytotoxic activity on several physiological processes of different species. In the current study, the allelopathic potential of D. viscosa VOCs, released by its foliage, was evaluated on seed germination and root growth of lettuce. The VOCs effect was also studied on lettuce adult plants in microcosm systems, which better mimicked the open field conditions. D. viscosa VOCs inhibited both seed germination and root growth of lettuce. The VOCs composition revealed a large presence of terpenoids, responsible of the effects observed. Moreover, D. viscosa VOCs caused an alteration on plant water status accompanied by oxidative damages and photoinhibition on lettuce adult plants., Competing Interests: The authors have declared that no competing interests exist.

Transplastomic (chloroplast genome-modified; CGM) lettuce that dominantly accumulates astaxanthin grows similarly to a non-transgenic control with almost no accumulation of naturally occurring photosynthetic carotenoids. In this study, we evaluated the activity and assembly of PSII in CGM lettuce. The maximum quantum yield of PSII in CGM lettuce was <0.6; however, the quantum yield of PSII was comparable with that in control leaves under higher light intensity. CGM lettuce showed a lower ability to induce non-photochemical quenching (NPQ) than the control under various light intensities. The fraction of slowly recovering NPQ in CGM lettuce, which is considered to be photoinhibitory quenching (qI), was less than half that of the control. In fact, 1 O 2 generation was lower in CGM than in control leaves under high light intensity. CGM lettuce contained less PSII, accumulated mostly as a monomer in thylakoid membranes. The PSII monomers purified from the CGM thylakoids bound echinenone and canthaxanthin in addition to β-carotene, suggesting that a shortage of β-carotene and/or the binding of carbonyl carotenoids would interfere with the photophysical function as well as normal assembly of PSII. In contrast, high accumulation of astaxanthin and other carbonyl carotenoids was found within the thylakoid membranes. This finding would be associated with the suppression of photo-oxidative stress in the thylakoid membranes. Our observation suggests the importance of a specific balance between photoprotection and photoinhibition that can support normal photosynthesis in CGM lettuce producing astaxanthin., (© The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Ultraviolet-B (UV-B) radiation is one of the most important abiotic stress factors that could influence plant growth, development, and productivity. Nitric oxide (NO) is an important plant growth regulator involved in a wide variety of physiological processes. In the present study, the possibility of enhancing UV-B stress tolerance of lettuce seedlings by the exogenous application of sodium nitroprusside (SNP) was investigated. UV-B radiation increased the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and total phenolic concentrations, antioxidant capacity, and expression of phenylalanine ammonia lyase (PAL) gene in seedlings, but the combination of SNP pretreatment and UV-B enhanced antioxidant enzyme activities, total phenolic concentrations, antioxidant capacity, and PAL gene expression even more. Moreover, UV-B radiation significantly inhibited chlorophylls, carotenoid, gibberellic acid (GA), and indole-3-acetic acid (IAA) contents and increased the contents of abscisic acid (ABA), salicylic acid (SA), malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide radical (O2•(-)) in lettuce seedlings. When SNP pretreatment was combined with the UV-B radiation, we observed alleviated chlorophylls, carotenoid, GA, and IAA inhibition and decreased content of ABA, SA, MDA, H2O2, and O2•(-) in comparison to non-pretreated stressed seedlings.

Purple lettuce was grown hydroponically under six different nitrogen nutrition conditions, with NO(3-)-N:NH(4+)-N at 1:0, 4:1 and 1:1 combined with nitrogen application levels of 10 and 15 mmol · L(-1), for 25 days in solar greenhouse, then treated with short-term continuous lighting (SCL) before harvest to study the changes in contents of nutrients and analyze the effects of nitrogen nutrition conditions on the changes. Results showed that the shoot dry mass of all six nitrogen nutrition conditions were significantly improved under SCL treatment, by 35.1% at least, and the root dry mass increased greatly except for NO(3-)-N:NH(4+)-N 1:1 combined with nitrogen application level 15 mmol · L(-1) treatment and NO(3-)-N:NH(4+)-N 1:0 combined with nitrogen application level 10 mmol · L(-1) treatment. The relative contents of total phenols and flavonoid of different nitrogen nutrition conditions turned significantly different after treatment with SCL. The relative contents of total phenols and flavonoid were enhanced with the improvement of ammonium nitrogen ratio, while the relative content of anthocyanin increased and then decreased with the improvement of ammonium nitrogen ratio. The lighting treatment reduced the nitrate content of leaf blade of all six nitrogen nutrition conditions remarkably by 23.2% at least. The contents of ascorbic acid, soluble sugar and soluble protein rose significantly under SCL treatments. The study showed that the reduction of nitrate content speeded up with the enhancement of nitrogen application level and ammonium nitrogen ratio, and the advancement of ascorbic acid content slowed down with the increasing nitrogen application level. The soluble sugar improvement speed increased with the increasing ammonium nitrogen ratio, and SCL lifted the dry mass of the lettuce greatly. The results showed that SCL with LED lamps improved significantly the dry matter of lettuce under different nitrogen nutrition conditions, reduced the nitrate content and increased the ascorbic acid, soluble sugar and soluble protein contents greatly. In addition, nitrogen nutrition conditions affected the effectiveness of short-term continuous lighting on quality improvement rate of hydroponic lettuce remarkably.

Common problems in a windowfarm system (a vertical and indoor hydroponic system) are phytopathogen infections in plants and excessive buildup of biofilms. The objectives of this study were (i) to promote plant health by making plants more resistant to infection by using beneficial biosurfactant-producing Pseudomonas chlororaphis around the roots and (ii) to minimize biofilm buildup by ultraviolet (UV) irradiation of the water reservoir, thereby extending the lifespan of the whole system with minimal maintenance. Pseudomonas chlororaphis-treated lettuce grew significantly better than nontreated lettuce, as indicated by enhancement of color, mass, length, and number of leaves per head (p < 0.05). The death rate of the lettuce was reduced by ∼ 50% when the lettuce was treated with P. chlororaphis. UV irradiation reduced the bacteria (4 log reduction) and algae (4 log reduction) in the water reservoirs and water tubing systems. Introduction of P. chlororaphis into the system promoted plant growth and reduced damage caused by the plant pathogen Pythium ultimum. UV irradiation of the water reservoir reduced algal and biofilm growth and extended the lifespan of the system.

Background: The inactivation of biofilms formed by pathogenic bacteria on ready-to-eat and minimally processed fruits and vegetables by nonthermal processing methods is critical to ensure food safety. Pulsed ultraviolet (PUV) light has shown promise in the surface decontamination of liquid, powdered, and solid foods. In this study, the antimicrobial efficacy of PUV light treatment on nascent biofilms formed by Escherichia coli O157:H7 and Listeria monocytogenes on the surfaces of food packaging materials, such as low-density polyethylene (LDPE), and fresh produce, such as lettuce (Lactuca sativa) leaves, was investigated., Results: The formation of biofilms on Romaine lettuce leaves and LDPE films was confirmed by crystal violet and Alcian blue staining methods. Inactivation of cells in the biofilm was determined by standard plating procedures, and by a luminescence-based bacterial cell viability assay. Upon PUV treatment of 10 s at two different light source to sample distances (4.5 and 8.8 cm), viable cell counts of L. monocytogenes and E. coli O157:H7 in biofilms on the lettuce surface were reduced by 0.6-2.2 log CFU mL(-1) and 1.1-3.8 log CFU mL(-1), respectively. On the LDPE surface, the efficiency of inactivation of biofilm-encased cells was slightly higher. The maximum values for microbial reduction on LDPE were 2.7 log CFU mL(-1) and 3.9 log CFU mL(-1) for L. monocytogenes and E. coli O157:H7, respectively. Increasing the duration of PUV light exposure resulted in a significant (P < 0.05) reduction in biofilm formation by both organisms. The results also revealed that PUV treatment was more effective at reducing E. coli biofilms compared with Listeria biofilms. A moderate increase in temperature (~7-15°C) was observed for both test materials., Conclusions: PUV is an effective nonthermal intervention method for surface decontamination of E. coli O157:H7 and L. monocytogenes on fresh produce and packaging materials.

UV-B radiation is often viewed as a source of stress for higher plants. In particular, photosynthetic function has been described as a common target for UV-B impairment; yet as our understanding of UV-B photomorphogenesis increases, there are opportunities to expand the emerging paradigm of regulatory UV response. Lactuca sativa is an important dietary crop species and is often subjected to rapid sunlight exposure at field transfer. Acclimation to UV-B and visible light conditions in L. sativa was dissected using gas exchange and chlorophyll fluorescence measurements, in addition to non-destructive assessments of UV epidermal shielding (SUV ). After UV-B treatment, seedlings were subjected to wide-range metabolomic analysis using liquid chromatography hybrid quadrupole time-of-flight high-resolution mass spectrometry (LC-QTOF-HRMS). During the acclimation period, net photosynthetic rate increased in UV-treated plants, epidermal UV shielding increased in both subsets of plants transferred to the acclimatory conditions (UV+/UV- plants) and Fv /Fm declined slightly in UV+/UV- plants. Metabolomic analysis revealed that a key group of secondary compounds was up-regulated by higher light conditions, yet several of these compounds were elevated further by UV-B radiation. In conclusion, acclimation to UV-B radiation involves co-protection from the effects of visible light, and responses to UV-B radiation at a photosynthetic level may not be consistently viewed as damaging to plant development., (© 2014 John Wiley & Sons Ltd.)

Time-averaged net photosynthetic rate (P n) under pulsed light (PL) is known to be affected by the PL frequency and duty ratio, even though the time-averaged photosynthetic photon flux density (PPFD) is unchanged. This phenomenon can be explained by considering that photosynthetic intermediates (PIs) are pooled during light periods and then consumed by partial photosynthetic reactions during dark periods. In this study, we developed a kinetic model to estimate P n of cos lettuce (Lactuca sativa L. var. longifolia) leaves under PL based on the dynamics of the amount of pooled PIs. The model inputs are average PPFD, duty ratio, and frequency; the output is P n. The rates of both PI accumulation and consumption at a given moment are assumed to be dependent on the amount of pooled PIs at that point. Required model parameters and three explanatory variables (average PPFD, frequency, and duty ratio) were determined for the simulation using P n values under PL based on several combinations of the three variables. The model simulation for various PL levels with a wide range of time-averaged PPFDs, frequencies, and duty ratios further demonstrated that P n under PL with high frequencies and duty ratios was comparable to, but did not exceed, P n under continuous light, and also showed that P n under PL decreased as either frequency or duty ratio was decreased. The developed model can be used to estimate P n under various light environments where PPFD changes cyclically.

Background: The modular body structure of plants enables detached plant organs, such as postharvest fruits and vegetables, to maintain active responsiveness to environmental stimuli, including daily cycles of light and darkness. Twenty-four hour light/darkness cycles entrain plant circadian clock rhythms, which provide advantage to plants. Here, we tested whether green leafy vegetables gain longevity advantage by being stored under light/dark cycles designed to maintain biological rhythms., Results: Light/dark cycles during postharvest storage improved several aspects of plant tissue performance comparable to that provided by refrigeration. Tissue integrity, green coloration, and chlorophyll content were generally enhanced by cycling of light and darkness compared to constant light or darkness during storage. In addition, the levels of the phytonutrient glucosinolates in kale and cabbage remained at higher levels over time when the leaf tissue was stored under light/dark cycles., Conclusions: Maintenance of the daily cycling of light and dark periods during postharvest storage may slow the decline of plant tissues, such as green leafy vegetables, improving not only appearance but also the health value of the crops through the maintenance of chlorophyll and phytochemical content after harvest.

This study investigated the effect of low-level photosynthetic photon flux density (PPFD; 43-230 μmol m(-2) s(-1)) on the major phenolic compounds of red leaf lettuce in three growth stages, before, during, and after head formation, using HPLC-DAD-ESI-MS(2) and evaluating via multiple regression analysis. Generally, the light-related increase of flavonoid glycosides was structure and growth stage-dependent. In detail, an interaction was detected between plant age and PPFD regarding cyanidin-3-O-(6"-O-malonyl)-glucoside concentration: the increase was strongest before head formation. The relationship between PPFD and quercetin-3-O-(6"-O-malonyl)-glucoside concentration was linear, whereas the increase of quercetin-3-O-glucoside and -3-O-glucuronide concentrations abated with increasing PPFD. Independent of growth stage, the caffeic acid derivatives concentration was not related to PPFD. All major phenolic compounds decreased with plant age. These results show the differential regulation of cyanidin, quercetin, and caffeic acid derivatives in lettuce, although closely connected biosynthetically, and emphasize the importance of ontogeny in the study of plant physiology.

Lettuce (Lactuca sativa) was hydroponically cultured in a completely enclosed plant factory, in which spectrum proportion-adjustable LED panels were used as sole light source for plant growth. Absorption and content of eleven mineral elements such as K, P, Ca, Mg, Na, Fe, Mn, Zn, Cu, B and Mo in Lactuca sativa under different spectral component conditions were studied by ICP -AES technology. The results showed that: (1) Single or combined spectrums corresponding to the absorbing peaks of chlorophyll a and b (450, 660 nm) could enhance the absorbing ability of roots especially for mineral elements Na, Fe, Mn, Cu and Mo, the single red spectrum had the most significant promoting effect under which contents of those four elements were respectively 7. 8, 4. 2, 4. 0 and 3. 7 times more than that under FL; (2) Absorption of K and B was the highest under FL which was 10. 309 mg g-1 and 32. 6 microg g-1 while the values decreased significantly under single or combined spectrum of red and blue; (3) Plants grown under single blue spectrum had the lowest absorption of Ca and Mg which respectively decreased by 35% and 33% than FL; (4) Lettuce grown under the spectrum combination of 30% blue and 70% red had the highest accumulations of biomass while those grown under 20% blue and 80% red had the highest accumulations of the following seven elements Ca, Mg, Na, Fe, Mn, Zn and B. The results provided theoretical basis for adjusting nutrient solution formula and selecting light spectrum of hydroponic lettuce.