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The red and far-red light photoreceptor phytochrome B (phyB) transmits light signals following cytosol-to-nuclear translocation to regulate transcriptional networks therein. This necessitates changes in protein-protein interactions of phyB in the cytosol, about which little is presently known. Via introduction of a nucleus-excluding G767R mutation into the dominant, constitutively active phyBY276H (YHB) allele, we explore the functional consequences of expressing a cytosol-localized YHBG767R variant in transgenic Arabidopsis seedlings. We show that YHBG767R elicits selective constitutive photomorphogenic phenotypes in dark-grown phyABCDE null mutants, wild type and other phy-deficient genotypes. These responses include light-independent apical hook opening, cotyledon unfolding, seed germination and agravitropic hypocotyl growth with minimal suppression of hypocotyl elongation. Such phenotypes correlate with reduced PIF3 levels, which implicates cytosolic targeting of PIF3 turnover or PIF3 translational inhibition by YHBG767R. However, as expected for a cytoplasm-tethered phyB, YHBG767R elicits reduced light-mediated signaling activity compared with similarly expressed wild-type phyB in phyABCDE mutant backgrounds. YHBG767R also interferes with wild-type phyB light signaling, presumably by formation of cytosol-retained and/or otherwise inactivated heterodimers. Our results suggest that cytosolic interactions with PIFs play an important role in phyB signaling even under physiological conditions.

Cryptochromes are widely dispersed flavoprotein photoreceptors that regulate numerous developmental responses to light in plants, as well as to stress and entrainment of the circadian clock in animals and humans. All cryptochromes are closely related to an ancient family of light-absorbing flavoenzymes known as photolyases, which use light as an energy source for DNA repair but themselves have no light sensing role. Here we review the means by which plant cryptochromes acquired a light sensing function. This transition involved subtle changes within the flavin binding pocket which gave rise to a visual photocycle consisting of light-inducible and dark-reversible flavin redox state transitions. In this photocycle, light first triggers flavin reduction from an initial dark-adapted resting state (FADox). The reduced state is the biologically active or ‘lit’ state, correlating with biological activity. Subsequently, the photoreduced flavin reoxidises back to the dark adapted or ‘resting’ state. Because the rate of reoxidation determines the lifetime of the signaling state, it significantly modulates biological activity. As a consequence of this redox photocycle Crys respond to both the wavelength and the intensity of light, but are in addition regulated by factors such as temperature, oxygen concentration, and cellular metabolites that alter rates of flavin reoxidation even independently of light. Mechanistically, flavin reduction is correlated with conformational change in the protein, which is thought to mediate biological activity through interaction with biological signaling partners. In addition, a second, entirely independent signaling mechanism arises from the cryptochrome photocycle in the form of reactive oxygen species (ROS). These are synthesized during flavin reoxidation, are known mediators of biotic and abiotic stress responses, and have been linked to Cry biological activity in plants and animals. Additional special properties arising from the cryptochrom

Cryptochromes are widely dispersed flavoprotein photoreceptors that regulate numerous developmental responses to light in plants, as well as to stress and entrainment of the circadian clock in animals and humans. All cryptochromes are closely related to an ancient family of light-absorbing flavoenzymes known as photolyases, which use light as an energy source for DNA repair but themselves have no light sensing role. Here we review the means by which plant cryptochromes acquired a light sensing function. This transition involved subtle changes within the flavin binding pocket which gave rise to a visual photocycle consisting of light-inducible and dark-reversible flavin redox state transitions. In this photocycle, light first triggers flavin reduction from an initial dark-adapted resting state (FADox). The reduced state is the biologically active or ‘lit’ state, correlating with biological activity. Subsequently, the photoreduced flavin reoxidises back to the dark adapted or ‘resting’ state. Because the rate of reoxidation determines the lifetime of the signaling state, it significantly modulates biological activity. As a consequence of this redox photocycle Crys respond to both the wavelength and the intensity of light, but are in addition regulated by factors such as temperature, oxygen concentration, and cellular metabolites that alter rates of flavin reoxidation even independently of light. Mechanistically, flavin reduction is correlated with conformational change in the protein, which is thought to mediate biological activity through interaction with biological signaling partners. In addition, a second, entirely independent signaling mechanism arises from the cryptochrome photocycle in the form of reactive oxygen species (ROS). These are synthesized during flavin reoxidation, are known mediators of biotic and abiotic stress responses, and have been linked to Cry biological activity in plants and animals. Additional special properties arising from the cryptochrom, Cryptochromes are widely dispersed flavoprotein photoreceptors that regulate numerous developmental responses to light in plants, as well as to stress and entrainment of the circadian clock in animals and humans. All cryptochromes are closely related to an ancient family of light-absorbing flavoenzymes known as photolyases, which use light as an energy source for DNA repair but themselves have no light sensing role. Here we review the means by which plant cryptochromes acquired a light sensing function. This transition involved subtle changes within the flavin binding pocket which gave rise to a visual photocycle consisting of light-inducible and dark-reversible flavin redox state transitions. In this photocycle, light first triggers flavin reduction from an initial dark-adapted resting state (FADox). The reduced state is the biologically active or ‘lit’ state, correlating with biological activity. Subsequently, the photoreduced flavin reoxidises back to the dark adapted or ‘resting’ state. Because the rate of reoxidation determines the lifetime of the signaling state, it significantly modulates biological activity. As a consequence of this redox photocycle Crys respond to both the wavelength and the intensity of light, but are in addition regulated by factors such as temperature, oxygen concentration, and cellular metabolites that alter rates of flavin reoxidation even independently of light. Mechanistically, flavin reduction is correlated with conformational change in the protein, which is thought to mediate biological activity through interaction with biological signaling partners. In addition, a second, entirely independent signaling mechanism arises from the cryptochrome photocycle in the form of reactive oxygen species (ROS). These are synthesized during flavin reoxidation, are known mediators of biotic and abiotic stress responses, and have been linked to Cry biological activity in plants and animals. Additional special properties arising from the cryptoch

In the absence of light signals, Arabidopsis plants fail to develop the rosette habit typical for this species. Instead, plants display caulescent growth due to elongation of rosette internodes. This aspect of photomorphogenic development has been paid little attention and molecular events involved, downstream of photoreceptor signaling, remain to be identified. Using a combination of genetic and molecular approaches, we show that Arabidopsis rosette habit is a photomorphogenic trait controlled by induction of ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1) as downstream target of multiple photoreceptors. ATH1 induction prevents rosette internode elongation by maintaining the shoot apical meristem (SAM) rib zone area inactive and requires inactivation of photomorphogenesis inhibitors, including PHYTOCHROME INTERACTING FACTOR (PIF) proteins. ATH1 activity results in tissue-specific inhibition of PIF expression, establishing double-negative feedback-regulation at the SAM. Light-requirement for ATH1 expression can be overcome by high sugar availability to the SAM. Both sugar and light signals that induce ATH1 and, subsequently, rosette habit are mediated by TOR kinase. Collectively, our data reveal a SAM-specific, double-negative ATH1-PIF feedback loop at the basis of rosette habit. Upstream, TOR kinase functions as central hub integrating light and energy signals that control this for Arabidopsis quintessential trait.

The development of a seedling into a photosynthetically active plant is a crucial process. Despite its importance, we do not fully understand the regulatory mechanisms behind the establishment of functional chloroplasts. We herein provide new insight into the early light response by identifying the function of three basic region/leucine zipper (bZIP) transcription factors: bZIP16, bZIP68, and GBF1. These proteins are involved in the regulation of key components required for the establishment of photosynthetically active chloroplasts. The activity of these bZIPs is dependent on the redox status of a conserved cysteine residue, which provides a mechanism to finetune light-responsive gene expression. The blue light cryptochrome (CRY) photoreceptors provide one of the major light-signaling pathways, and bZIP target genes overlap with one-third of CRY-regulated genes with an enrichment for photosynthesis/chloroplast-associated genes. bZIP16, bZIP68, and GBF1 were demonstrated as novel interaction partners of CRY1. The interaction between CRY1 and bZIP16 was stimulated by blue light. Furthermore, we demonstrate a genetic link between the bZIP proteins and cryptochromes as the cry1cry2 mutant is epistatic to the cry1cry2bzip16bzip68gbf1 mutant. bZIP16, bZIP68, and GBF1 regulate a subset of photosynthesis associated genes in response to blue light critical for a proper greening process in Arabidopsis.

The correct development of seeds is a pivotal requirement for species preservation. This process depends on the balance between sensing the environmental stimuli/stressors and hormone-mediated transduction, which results in physiological responses. The red and blue regions of the electromagnetic spectrum are known to influence seed dormancy and germination. Here, we report on the effects induced by the blue (peak at 430 nm) and red (peak at 650 nm) regions of the electromagnetic spectrum on seeds from photo- and skotomorphogenetic capsules developed under white, blue, or red light. Regardless of exposure, seeds from skotomorphogenetic capsules showed an almost absent dormancy in association with altered germination kinetics. Conversely, in seeds from photomorphogenetic capsules, the exposure to the blue region induced skotomorphogenetic-like effects, while the exposure to the whole visible range (350–750 nm), as well as to only the red region, showed a dose-related trend. The observed differences appeared to be dependent on the wavelengths in the red and to be based on transduction mechanisms taking place in fruits. While the molecular bases of this differential effect need to be clarified, the results hint at the role played by different light wavelengths and intensities in seed development and germination. These findings may be relevant for applications in crop production and species safeguarding.

Plastid-to-nucleus retrograde signalling (RS) initiated by dysfunctional chloroplasts impact photomorphogenic development. We have previously shown that the transcription factor GLK1 acts downstream of the RS regulator GUN1 in photodamaging conditions to regulate not only the well established expression of photosynthesis-associated nuclear genes (PhANGs) but also to regulate seedling morphogenesis. Specifically, the GUN1/GLK1 module inhibits the light-induced phytochrome-interacting factor (PIF)-repressed transcriptional network to suppress cotyledon development when chloroplast integrity is compromised, modulating the area exposed to potentially damaging high light. However, how the GUN1/GLK1 module inhibits photomorphogenesis upon chloroplast damage remained undefined., Here, we report the identification of BBX16 as a novel direct target of GLK1. BBX16 is induced and promotes photomorphogenesis in moderate light and is repressed via GUN1/GLK1 after chloroplast damage. Additionally, we showed that BBX16 represents a regulatory branching point downstream of GUN1/GLK1 in the regulation of PhANG expression and seedling development upon RS activation., The gun1 phenotype in lincomycin and the gun1-like phenotype of GLK1OX are markedly suppressed in gun1bbx16 and GLK1OXbbx16., This study identified BBX16 as the first member of the BBX family involved in RS, and defines a molecular bifurcation mechanism operated by GLK1/BBX16 to optimise seedling de-etiolation, and to ensure photoprotection in unfavourable light conditions.

Chloroplast biogenesis during seedling development of angiosperms is a rapid and highly dynamic process that parallels the light-dependent photomorphogenic programme. Pre-treatments of dark-grown seedlings with lincomyin or norflurazon prevent chloroplast biogenesis upon illumination yielding albino seedlings. A comparable phenotype was found for the Arabidopsis mutant plastid-encoded polymerase associated protein 7 (pap7) being defective in the prokaryotic-type plastid RNA polymerase. In all three cases the defect in plastid function has a severe impact on the expression of nuclear genes representing the influence of retrograde signaling pathway(s) from the plastid. We performed a meta-analysis of recently published genome-wide expression studies that investigated the impact of the aforementioned chemical and genetic blocking of chloroplast biogenesis on nuclear gene expression profiles. We identified a core module of 152 genes being affected in all three conditions. These genes were classified according to their function and analyzed with respect to their implication in retrograde signaling and chloroplast biogenesis. Our study uncovers novel genes regulated by retrograde biogenic signals and suggests the action of a common signaling pathway that is used by signals originating from plastid transcription, translation and oxidative stress.

Influence of spectral manipulation of light using coloured nets and seasonal variation on cut foliage yield and quality of Philodendron ‘Xanadu’ was evaluated under red, green, white and black coloured shade nets permitting light intensities ranging from 240.50 to 370μ mol m-2 s-1 (75% shade net), for two consecutive years from 2014-16, at ICARIIHR, Bengaluru. The plants grown under white shade net (75% shade) resulted in higher foliage production plant-1month-1 (14.53) and were on par with those grown under green shade net. The quality of the cut foliage in plants grown under white shade net with respect to stalk length (24.91 cm) and width of the lamina (5.19 cm) was on par with those under green and black shade nets. Coloured shade nets did not influence the vase life of the cut foliage. Developmental stages of the foliage under the different coloured nets have indicated that leaves attained the harvestable maturity stage at 29.92 days post-emergence under white shade. Cultivation of Philodendron ‘Xanadu’ under white shade resulted in maximum cut foliage yield and quality.

While the use of narrowband irradiance regimes containing different blue light fractions has proven useful to unravel blue light effects on plants at a fundamental level, it does not quantify the responses to blue light under natural daylight conditions. The objective of this study is to understand the blue light growth responses by combining photosynthetic measurements with measurements of whole plant light absorption in a simulated daylight spectrum enriched with different levels of blue light. To achieve this, tomato plants were grown under six different combinations of artificial solar light and blue LED light. Light treatments were defined by the blue light (400–500 nm) fraction of total photosynthetic photon flux density (400–700 nm) and included 27 % (no additional blue LED), 28 %, 31 %, 38 %, 43 % and 61 % blue light with a total photosynthetic photon flux density of 100 μmol m−2 s-1 in all treatments. Whole plant light absorption was estimated by using ray tracing simulation combined with measured 3-dimensional structure of the plant and optical properties of the leaves. The total dry weight of the plants decreased linearly with the increase of blue light fraction; the dry weight of the plants grown under 27 % blue being 1.6 times greater than that of the plants grown under 61 % blue. This large difference was related to lower light absorption by the plants when fraction blue light increased, due to more compact morphology, i.e. lower leaf area, leaf length/width ratio and shorter stem. Light-limited quantum yield and maximum photosynthetic capacity were not affected by blue light fraction. In the case of the latter, which in other studies has often been found to be positively related to blue light fraction, it may be that the blue light fraction already present in the daylight source had saturated this response. Overall, increasing the blue light fraction in a solar light background decreases growth mainly through its effect on pla

Tomato INDOLE-3-ACETIC ACID9 (SlIAA9) is a transcriptional repressor in auxin signal transduction, and SlIAA9 knockout tomato plants develop parthenocarpic fruits without fertilization. We generated sliaa9 mutants with parthenocarpy in several commercial tomato cultivars (Moneymaker, Rio Grande, and Ailsa Craig) using CRISPR-Cas9, and null-segregant lines in the T1 generation were isolated by self-pollination, which was confirmed by PCR and Southern blot analysis. We then estimated shoot growth phenotypes of the mutant plants under different light (low and normal) conditions. The shoot length of sliaa9 plants in Moneymaker and Rio Grande was smaller than those of wild-type cultivars in low light conditions, whereas there was not clear difference between the mutant of Ailsa Craig and the wild-type under both light conditions. Furthermore, young seedlings in Rio Grande exhibited shade avoidance response in hypocotyl growth, in which the hypocotyl lengths were increased in low light conditions, and sliaa9 mutant seedlings of Ailsa Craig exhibited enhanced responses in this phenotype. Fruit production and growth rates were similar among the sliaa9 mutant tomato cultivars. These results suggest that control mechanisms involved in the interaction of AUX/IAA9 and lights condition in elongation growth differ among commercial tomato cultivars.

For decisions on supplemental lighting a quantitative knowledge of the plants' responses to light under varying conditions is fundamental. In this study, we developed light dose-response curves of growth and morphological traits for Ocimum basilicum L. and examined the effects of light color (blue, red, and white plus far-red) and natural environment (season) on these curves. Four greenhouse experiments were conducted throughout the year to determine the efficiencies of the light regimes on growth and their effects on plant morphology. A special aspect was the photosynthetic efficiency of far-red light. Linear and monomolecular relationships were found for the relationships between plant traits and supplemental light dose. Traits related to biomass productivity increased linearly with light dose whereas some morphological characters showed a saturation behavior. Red light and white plus far-red light were more efficient in plant dry weight production than blue light, and the plants adapted differently to the light qualities: higher biomass under red light was related to a plant architecture more favorable for light capture, i.e., taller plants and bigger leaves. White plus far-red light, on the other hand, increased leaf mass per area (LMA) and light use efficiency (LUE). Blue light resulted in lowest plant light interception and LUE. Considering photosynthetic effects of near-infrared light (PPFD800, 400–800 nm) instead of photosynthetic photon flux density (PPFD700, 400–700 nm) led to strongly reduced efficiencies. Traits related to photosynthesis such as dry weight, LMA and LUE were particularly affected by PPFD800. There were no interactions between the efficiencies of the different light colors and the seasons. Efficiencies of all light regimes were significantly lower during summer compared to spring and winter. Higher dry weight production during summer compared to winter and spring were a consequence of increased light interception rather than changes in LUE

DE-ETIOLATED 1 (DET1) and CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1) are two essential repressors of Arabidopsis photomorphogenesis. These proteins can associate with CULLIN4 to form independent CRL4-based E3 ubiquitin ligases that mediate the degradation of several photomorphogenic transcription factors, including ELONGATED HYPOCOTYL 5 (HY5), thereby controlling multiple gene-regulatory networks. Despite extensive biochemical and genetic analyses of their multi-subunit complexes, the functional links between DET1 and COP1 have long remained elusive. Here, we report that DET1 associates with COP1 in vivo, enhances COP1-HY5 interaction, and promotes COP1 destabilization in a process that dampens HY5 protein abundance. By regulating its accumulation, DET1 avoids HY5 association with hundreds of second-site genomic loci, which are also frequently targeted by the skotomorphogenic transcription factor PHYTOCHROME-INTERACTING FACTOR 3. Accordingly, ectopic HY5 chromatin enrichment favors local gene repression and can trigger fusca-like phenotypes. This study therefore shows that DET1-mediated regulation of COP1 stability tunes down the HY5 cistrome, avoiding hyper-photomorphogenic responses that might compromise plant viability.

Producción Científica, Stem straightness is related to wood quality and yield. Although important genetic differences in stem straightness among the natural populations of Pinus pinaster are well established, the main drivers of these differences are not well known. Since the responses of trees to light are key ecological features that induce stem curvature, we hypothesized that populations with better straightness should exhibit lower photomorphogenetic and phototropic sensitivity. We compared three populations to identify the main processes driven by primary and secondary growth that explain their differences in response to light. One-year-old seedlings were grown under two treatments—direct sunlight and lateral light plus shade—for a period of 5 months. The length and the leaning of the stems were measured weekly. The asymmetry of radial growth and compression wood (CW) formation were analyzed in cross-sections. We found differences among the populations in photomorphogenetic and phototropic reactions. However, the population with straighter stems was not characterized by reduced sensitivity to light. Photo(gravi)tropic responses driven by primary growth and gravitropic responses driven by secondary growth explained the kinetics of the stem leaning and CW pattern. Asymmetric radial growth and CW formation did not contribute to the phototropic reactions., Comisión Interministerial de Ciencia y Tecnología (projects AGF97-0809 and AGL2004-07094-C02-02)

Shading by sunlit leaves causes a low red (R) to far-red (FR) ratio that results in a low phytochrome stationary state (PSS). A low PSS induces an array of shade avoidance responses that influence plant architecture and development. It has often been suggested that this architectural response is advantageous for plant growth due to its positive effect on light interception. In contrast to sunlight, artificial light sources such as LEDs often lack FR, resulting in a PSS value higher than solar light (∼0.70). The aim of this study was to investigate how PSS values higher than solar radiation influence the growth and development of tomato plants. Additionally, we investigated whether a short period of FR at the end of the day (EOD-FR) could counteract any potentially negative effects caused by a lack of FR during the day. Tomato plants were grown at four PSS levels (0.70, 0.73, 0.80, and 0.88), or with a 15-min end-of-day far-red (EOD-FR) application (PSS 0.10). Photosynthetic Active Radiation (PAR; 150 μmol m -2 s -1 ) was supplied using red and blue (95/5%) LEDs. In an additional experiment, the same treatments were applied to plants receiving supplementary low-intensity solar light. Increasing PSS above solar PSS resulted in increased plant height. Leaf area and plant dry mass were lower in the treatments completely lacking FR than treatments with FR. EOD-FR-treated plants responded almost similarly to plants grown without FR, except for plant height, which was increased. Simulations with a 3D-model for light absorption revealed that the increase in dry mass was mainly related to an increase in light absorption due to a higher total leaf area. Increased petiole angle and internode length had a negative influence on total light absorption. Additionally, the treatments without FR and the EOD-FR showed strongly reduced fruit production due to reduced fruit growth associated with reduced source strength and delayed flowering. We conclude that g

Photosynthetic organisms use nonphotochemical quenching (NPQ) mechanisms to dissipate excess absorbed light energy and protect themselves from photooxidation. In the model green alga Chlamydomonas reinhardtii, the capacity for rapidly reversible NPQ (qE) is induced by high light, blue light, and UV light via increased expression of LHCSR and PSBS genes that are necessary for qE. Here, we used a forward genetics approach to identify SPA1 and CUL4, components of a putative green algal E3 ubiquitin ligase complex, as critical factors in a signaling pathway that controls light-regulated expression of the LHCSR and PSBS genes in C. reinhardtii The spa1 and cul4 mutants accumulate increased levels of LHCSR1 and PSBS proteins in high light, and unlike the wild type, they express LHCSR1 and exhibit qE capacity even when grown in low light. The spa1-1 mutation resulted in constitutively high expression of LHCSR and PSBS RNAs in both low light and high light. The qE and gene expression phenotypes of spa1-1 are blocked by mutation of CrCO, a B-box Zn-finger transcription factor that is a homolog of CONSTANS, which controls flowering time in plants. CONSTANS-like cis-regulatory sequences were identified proximal to the qE genes, consistent with CrCO acting as a direct activator of qE gene expression. We conclude that SPA1 and CUL4 are components of a conserved E3 ubiquitin ligase that acts upstream of CrCO, whose regulatory function is wired differently in C. reinhardtii to control qE capacity via cis-regulatory CrCO-binding sites at key photoprotection genes.

Next to its intensity, the spectral composition of light is one of the most important factors affecting plant growth and morphology. The introduction of light emitting diodes (LEDs) offers perspectives to design optimal light spectra for plant production systems. However, knowledge on the effects of light quality on physiological plant processes is still limited. The aim of this study is to determine the effects of six light qualities on growth and plant architecture of young tomato plants, and to upscale these effects to the crop level using a multispectral, functional-structural plant model. Young tomato plants were grown under 210 μmol m-2 s-1 blue, green, amber, red, white or red/blue (92%/8%) LED light with a low intensity of sunlight as background. Plants grown under blue light were shorter and developed smaller leaves which were obliquely oriented upward. Leaves grown under blue light contained the highest levels of light harvesting pigments, but when exposed to blue light only, they had the lowest rate of leaf photosynthesis. However, when exposed to white light these leaves had the highest rate of photosynthesis. Under green light, tomato plants were taller and leaves were nearly horizontally oriented, with a high specific leaf area. The open plant structure combined with a high light transmission and reflection at the leaf level allowed green light to penetrate deeper into the canopy. Plants grown under red, amber and white light were comparable with respect to height, leaf area and biomass production. The 3D model simulations indicated that the observed changes in plant architecture had a significant impact on light absorbance at the leaf and crop level. The combination of plant architecture and spectrum dependent photosynthesis was found to result in the highest rate of crop photosynthesis under red light in plants initially grown under green light. These results suggest that dynamic light spectra may offer perspectives to increa

Plants have evolved a suite of photoreceptors to perceive information from the surrounding light conditions. The aim of this study was to examine photomorphogenic effects of light quality on the growth of Scots pine (Pinus sylvestris L.) seedlings representing southern (60 °N) and northern (68 °N) origins in Finland. We measured the growth characteristics and the expression of light-responsive genes from seedlings grown under two LED light spectra: (1) Retarder (blue and red wavelengths in ratio 0.7) inducing compact growth, and (2) Booster (moderate in blue, green and far-red wavelengths, and high intensity of red light) promoting shoot elongation. The results show that root elongation, biomass, and branching were reduced under Retarder spectrum in the seedlings representing both origins, while inhibition in seed germination and shoot elongation was mainly detected in the seedlings of northern origin. The expression of ZTL and HY5 was related to Scots pine growth under both light spectra. Moreover, the expression of PHYN correlated with growth when exposed to Retarder, whereas CRY2 expression was associated with growth under Booster. Our data indicates that blue light and the deficiency of far-red light limit the growth of Scots pine seedlings and that northern populations are more sensitive to blue light than southern populations. Furthermore, the data analyses suggest that ZTL and HY5 broadly participate in the light-mediated growth regulation of Scots pine, whereas PHYN responses to direct sunlight and the role of CRY2 is in shade avoidance. Altogether, our study extends the knowledge of light quality and differential gene expression affecting the early growth of Scots pines representing different latitudinal origins.

Plant photoreceptors detect changes in the light environment and induce differential gene expression, resulting in the appropriate physiological and morphological responses. Under full sunlight, phytochromes, cryptochromes and the UV-B photoreceptor, UVR8 (UV-B RESISTANCE LOCUS 8), destabilize PHYTOCHROME INTERACTING FACTORS (PIFs) to inhibit elongation. PIFs are transcriptions factors that inhibit light-regulated genes, including auxin-related genes involved in cell elongation. In the shaded environment, the reduction in the spectral composition detected by the photoreceptors results in the activation of elongation and PIF activity. However, recent studies have shown that low levels of UV-B can still inhibit the elongation under shade. Most photobiology studies that investigated plant responses to shade have concentrated on the model species, Arabidopsis thaliana. In contrast, Solanum lycopersicum (tomato) is another model system, but few studies have investigated plant responses to shade in tomato due to its sympodial architecture and presence of internodes which A. thaliana lacks. In this study, phytochrome and cryptochrome tomato mutants were exposed to low levels of UV-B under photosynthetically active radiation (PAR) as background light to investigate the possible crosstalk between these photoreceptors and the UV-B photoreceptor of tomato in regulating hypocotyl or internode elongation. Out of all the multiple phytochrome and one cryptochrome mutants, phyAphyB2 mutant exhibited an impaired UV-B inhibition of internode elongation after three days of UV-B treatment. End-point PCR on the gene expression of PIF4 together with two UV-B responsive genes and genes involved in the catabolism of active gibberellin could not explain the impaired response of phyAphyB2. Nevertheless, physiological measurements indicate that phyA and phyB2 of tomato may be acting redundantly in mediating the UV-B induced inhibition of internode.

HSFA9 is a seed-specific transcription factor that in sunflower (Helianthus annuus) is involved in desiccation tolerance and longevity. Here we show that the constitutive overexpression of HSFA9 in tobacco (Nicotiana tabacum) seedlings attenuated hypocotyl growth under darkness and accelerated the initial photosynthetic development. Plants overexpressing HSFA9 increased accumulation of carotenoids, chlorophyllide, and chlorophyll, and displayed earlier unfolding of the cotyledons. HSFA9 enhanced phytochrome-dependent light responses, as shown by an intensified hypocotyl length reduction after treatments with continuous far-red or red light. This observation indicated the involvement of at least two phytochromes: PHYA and PHYB. Reduced hypocotyl length under darkness did not depend on phytochrome photo-activation; this was inferred from the lack of effect observed using far-red light pulses applied before the dark treatment. HSFA9 increased the expression of genes that activate photomorphogenesis, including PHYA, PHYB, and HY5. HSFA9 might directly upregulate PHYA and indirectly affect PHYB transcription, as suggested by transient expression assays. Converse effects on gene expression, greening, and cotyledon unfolding were observed using a dominant-negative form of HSFA9, which was overexpressed under a seed-specific promoter. This work uncovers a novel transcriptional link, through HSFA9, between seed maturation and early photomorphogenesis. In all, our data suggest that HSFA9 enhances photomorphogenesis via early transcriptional effects that start in seeds under darkness

BackgroundIn cereal crops such as wheat, an optimal timing of developmental transitions is required to maximize grain yield. Many of these developmental changes are precisely regulated by changes in the duration, intensity or quality of light. Phytochromes are dimeric photoreceptors that absorb light maximally in the red and far-red wavelengths and induce large-scale transcriptional changes in response to variation in light quality. In wheat, PHYC is required for early flowering under long days. However, it is currently unknown whether this function requires the presence of PHYB. In this study, we characterized the role of PHYB in wheat development and used RNA-seq to analyze and compare the transcriptomes of phyB-null and phyC-null TILLING mutants.ResultsUnder long-day photoperiods, phyB-null plants exhibit a severe delay in flowering comparable to the delay observed in phyC-null plants. These results demonstrate that both genes are required for the induction of wheat flowering under long days. Using replicated RNA-seq studies we identified 82 genes that are significantly up or down regulated in both the phyB-null and phyC-null mutant relative to their respective wild-type controls. Among these genes are several well-characterized positive regulators of flowering, including PPD1, FT1 and VRN1. Eight-fold more genes were differentially regulated only in the phyB-null mutant (2202) than only in the phyC-null mutant (261). The PHYB-regulated genes were enriched in components of the auxin, gibberellin and brassinosteroid biosynthesis and signaling pathways, and in transcription factors with putative roles in regulating vegetative development and shade-avoidance responses. Several genes involved in abiotic stress tolerance pathways were also found to be regulated by PHYB.ConclusionsPHYB and PHYC are both required for the photoperiodic induction of wheat flowering, whereas PHYB alone regulates a large number of genes involved in hormone biosynthesis and signaling, shade

Plants respond to neighbor shade by increasing stem and petiole elongation. Shade, sensed by phytochrome photoreceptors, causes stabilization of PHYTOCHROME INTERACTING FACTOR proteins and subsequent induction of YUCCA auxin biosynthetic genes. To investigate the role of YUCCA genes in phytochrome-mediated elongation, we examined auxin signaling kinetics after an end-of-day far-red (EOD-FR) light treatment, and found that an auxin responsive reporter is rapidly induced within 2 hours of far-red exposure. YUCCA2, 5, 8, and 9 are all induced with similar kinetics suggesting that they could act redundantly to control shade-mediated elongation. To test this hypothesis we constructed a yucca2, 5, 8, 9 quadruple mutant and found that the hypocotyl and petiole EOD-FR and shade avoidance responses are completely disrupted. This work shows that YUCCA auxin biosynthetic genes are essential for detectable shade avoidance and that YUCCA genes are important for petiole shade avoidance.

De inzichten in het effect van lichtkleuren op fotosynthese, vorm en ontwikkeling groeien gestaag. Je zou dan graag willen dat het om simpele relaties gaat, bijvoorbeeld ‘blauw licht opent huidmondjes’. Zo ligt het echter vaak niet. Effecten op korte en lange termijn zijn vaak verschillend en het gaat altijd om de mix van kleuren.

De inzichten in het effect van lichtkleuren op fotosynthese, vorm en ontwikkeling groeien gestaag. Je zou dan graag willen dat het om simpele relaties gaat, bijvoorbeeld ‘blauw licht opent huidmondjes’. Zo ligt het echter vaak niet. Effecten op korte en lange termijn zijn vaak verschillend en het gaat altijd om de mix van kleuren.

[EN] In response to canopy shade, plant vegetative structures elongate to gain access to light. However, the mechanism that allows a plastic transcriptional response to canopy shade light is not fully elucidated. Here we propose that the activity of PIF4, a key transcription factor in the shade signalling network, is modulated by the interplay between the BBX24 transcriptional regulator and DELLA proteins, which are negative regulators of the gibberellin (GA) signalling pathway. We show that GA-related targets are enriched among genes responsive to BBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GA treatment that promotes DELLA degradation. BBX24 physically interacts with DELLA proteins and alleviates DELLA-mediated repression of PIF4 activity. The proposed molecular mechanism provides reversible regulation of the activity of a key transcription factor that may prove especially relevant under fluctuating light conditions.

The responses of three plant species, Glycine max L., Triticum aestivum L. and Helianthus annuus L., exposed to different doses of UV-C radiation applied in the seed were studied. The objective was to test the hypothesis that it is possible to find a dose of UV-C that positively modifies seed germination and heat stress tolerance. The results of the standard germination test showed that the variables associated with the germination vigor and percentage, the number and biomass of normal seedlings exhibited no response to the UV-C radiation in wheat and sunflower; conversely, soybean showed a negative response to these variables. UV-C radiation decreased the average length of the plumule, while the radicle average length showed no change in soybeans and wheat, and a positive effect in sunflower. After applying stress conditions of high temperature and humidity, a positive effect of UV-C radiation was observed, but only for variables of vigor and germination in sunflower and soybeans, with UV-C doses of 2.88-43.2 kj m-2 and 57.6 kj m-2, respectively. Conversely, the number of normal seedlings, the plumule and radicle biomass and the length, as well as the seedling biomass showed no changes with UV-C radiation., En la presente investigación se estudió la respuesta de Glycine max L., Triticum aestivum L. y Helianthus annuus L., a diferentes dosis de radiación UV-C aplicada en la semilla, bajo la hipótesis de que es posible encontrar una dosis de UV-C que modifique de forma positiva la germinación y la tolerancia al estrés de alta temperatura y humedad. Los resultados de la prueba de germinación estándar indican que las variables asociadas con el vigor germinativo como el porcentaje de germinación, el número de plántulas normales y la biomasa no mostraron respuesta a la irradiación con UV-C en el trigo y el girasol, mostrando la soya respuestas negativas en estas variables. La longitud media de la plúmula disminuyó con la irradiación mientras que la longitud media de la radícula no mostró cambio en la soya y el trigo, presentando efecto positivo el girasol. Después de aplicar las condiciones de estrés de alta temperatura y humedad se obtuvo un efecto positivo de la radiación UV-C en las variables de vigor y germinación en girasol y soya, con las dosis de 2.88-43.2 kj m-2 y 57.6 kj m-2, respectivamente. En cambio, el número de plántulas normales, la biomasa y la longitud de la plúmula y la radícula así como la biomasa de las plántulas no mostraron ningún efecto.

Plants possess multiple photoreceptors to mediate light regulation of growth and development, but it is not well understood how different photoreceptors coordinate their actions to jointly regulate developmental responses, such as flowering time. In Arabidopsis, the photoexcited cryptochrome 2 interacts with the transcription factor CRYPTOCHROME-INTERACTING basic helix-loop-helix 1 (CIB1) to activate transcription and floral initiation. We show that the CIB1 protein expression is regulated by blue light; CIB1 is highly expressed in plants exposed to blue light, but levels of the CIB1 protein decreases in the absence of blue light. We demonstrate that CIB1 is degraded by the 26S proteasome and that blue light suppresses CIB1 degradation. Surprisingly, although cryptochrome 2 physically interacts with CIB1 in response to blue light, it is not the photoreceptor mediating blue-light suppression of CIB1 degradation. Instead, two of the three light-oxygen-voltage (LOV)-domain photoreceptors, ZEITLUPE and LOV KELCH PROTEIN 2, but not FLAVIN-BINDING KELCH REPEAT 1, are required for the function and blue-light suppression of degradation of CIB1. These results support the hypothesis that the evolutionarily unrelated blue-light receptors, cryptochrome and LOV-domain F-box proteins, mediate blue-light regulation of the same transcription factor by distinct mechanisms.

Este estudio se orientó a establecer si la cantidad y la calidad de la luz afectan el crecimiento y desarrollo de las plantas de fresa. Las plantas se desarrollaron en un invernadero en Tunja / Colombia, bajo diferente calidad de luz (amarilla, verde, azul, transparente, roja y control sin cobertura de color), proporcionada por películas de polipropileno. Los filtros coloreados aportaron también diferentes niveles de sombreado a las plantas. Se calcularon los índices comúnmente utilizados para el análisis básico del crecimiento en vegetales. Los tratamientos se colocaron en un diseño en bloques al azar con diez replicaciones. Los filtros se ubicaron 1m sobre el follaje del cultivo, desde el trasplante hasta la cosecha de las plantas. La tasa de asimilación neta se redujo con las coberturas de color con excepción de la cobertura transparente y el control. La cobertura verde indujo un incremento en la relación de área foliar, la relación raíz : vástago, la relación de peso foliar y en el área foliar específica; sin embargo, el índice de cosecha, las tasa absoluta y relativa de crecimiento se redujeron en plantas que crecieron bajo esta cobertura. Las plantas expuestas a la película amarilla mostraron el mayor índice de cosecha. La respuesta de las plantas de fresa en relación con las tasas de crecimiento fueron la consecuencia del efecto conjunto de la cantidad y la calidad de la luz incidente.The present study sought to understand how quantity and quality of light affect growth and development in strawberry plants. Plants were grown in a greenhouse in Tunja, Colombia, under different light quality regimes provided by polypropylene films (yellow, green, blue, transparent, red, and a control without plastic film cover). These colored filters also provided different shading levels to plants. The authors measured growth parameters and calculated various indices commonly used in basic plant growth analysis. Plastic light filters were placed 1 m above crop foliage and were

The reversibly red (R)/far-red (FR)-light-responsive phytochrome (phy) photosensory system initiates both the deetiolation process in dark-germinated seedlings upon first exposure to light, and the shade-avoidance process in fully deetiolated seedlings upon exposure to vegetational shade. The intracellular signaling pathway from the light-activated photoreceptor conformer (Pfr) to the transcriptional network that drives these responses involves direct, physical interaction of Pfr with a small subfamily of bHLH transcription factors, termed Phy-Interacting Factors (PIFs), which induces rapid PIF proteolytic degradation. In addition, there is evidence of further complexity in light-grown seedlings, whereby phyB–PIF interaction reciprocally induces phyB degradation, in a mutually-negative, feedback-loop configuration. Here, to assess the relative contributions of these antagonistic activities to the net phenotypic readout in light-grown seedlings, we have examined the magnitude of the light- and simulated-shade-induced responses of a pentuple phyBpif1pif3pif4pif5 (phyBpifq) mutant and various multiple pif-mutant combinations. The data (1) reaffirm that phyB is the predominant, if not exclusive, photoreceptor imposing the inhibition of hypocotyl elongation in deetiolating seedlings in response to prolonged continuous R irradiation and (2) show that the PIF quartet (PIF1, PIF3, PIF4, and PIF5) retain and exert a dual capacity to modulate hypocotyl elongation under these conditions, by concomitantly promoting cell elongation through intrinsic transcriptional-regulatory activity, and reducing phyB-inhibitory capacity through feedback-loop-induced phyB degradation. In shade-exposed seedlings, immunoblot analysis shows that the shade-imposed reduction in Pfr levels induces increases in the abundance of PIF3, and mutant analysis indicates that PIF3 acts, in conjunction with PIF4 and PIF5, to promote the known shade-induced acceleration of hypocotyl elongation. Conversely, alt

Plants are stationary and need to adapt to the environment they live in. Integration of environmental cues, such as changes in light and temperature, can occur either directly or through the action of hormones. Hormone and light signaling leads to rapid changes in gene expression, and eventually changes in protein levels. In this thesis I have studied how the epigenetic regulator TERMINAL FLOWER2 (TFL2) is involved in light and hormonal signaling in the model organism Arabidopsis thaliana (thale cress). TFL2 is the only Arabidopsis homologue of HETEROCHROMATIN PROTEIN1 (HP1). HP1 proteins have been shown to be involved in repressing gene expression by maintaining the tight structure of heterochromatin or by forming a heterochromatin like structure in euchromatic regions. Unlike metazoan HP1 which can be localized both to eu- and heterochromatin, TFL2 is uniquely localized to euchromatin. tfl2 mutants have reduced levels of free auxin and a reduced rate of auxin biosynthesis. TFL2 binds to and promotes spatial and temporal expression of the genes belonging to the YUCCA gene family, which are believed to regulate a rate limiting step in the auxin biosynthesis pathway. Further, TFL2 binds to a subset of Aux/IAA proteins to repress auxin regulated genes involved in ovule and carpel development. In a similar way, TFL2 is also involved in repressing two jasmonate responsive genes, VEGETATIVE STORAGE PROTEIN1 and 2. This TFL2 regulated repression might occur through the interaction with the jasmonate responsive protein JAZ6. In light signaling TFL2 is involved in repressing both phytochrome A and B signaling as the response to red and far red light is enhanced in tfl2 mutants. The shade avoidance response and chloroplast biogenesis are also regulated by TFL2 as the hypocotyls of tfl2 are not able to elongate as wt in shade conditions and greening is delayed upon de-etiolation of tfl2 seedlings. This work shows that TFL2 has a repressive function in auxin, jasmonate and lig

Key words: action spectrum, artificial solar spectrum, blue light, Cucumis sativus, gas-exchange, light-emitting diodes (LEDs), light interception, light quality, non-photosynthetic pigments, photo-synthetic capacity, photomorphogenesis, photosystem excitation balance, quantum yield, red light. A wide range of plant properties respond to the spectral composition of irradiance, such as photosynthesis, photomorphogenesis, phototropism and photonastic movements. These responses affect plant productivity, mainly via changes in the photosynthetic rate per unit leaf area, light interception, and irradiance distribution through the canopy. The spectral environment of plants is dependent on location (e.g. latitude), changes over time (e.g. Sun-angle), shading by other leaves, and, in the case of protected cultivation, the use of growth lamps. Therefore, not only the acclimation of developing leaves to light spectrum is important for plant productivity and survival, but also the capability of mature leaves to respond to changes in spectrum. This thesis focuses on the acclimation of photosynthesis per unit leaf area to the growth-light spectrum, the consequences of spectral acclimation for the wavelength dependence of photosynthetic quantum yield, and photomorphogenetic versus leaf photosynthetic acclimation in relation to biomass production. Cucumis sativus is used as a model plant. Additionally, the consequences of the choice and quality of the actinic light used during photosynthesis measurements are explored. By growing plants under seven different combinations of red and blue light, blue light is shown to have both a qualitative and a quantitative effect on leaf development. Only leaves developed under red alone (0% blue) displayed a dysfunctional photosynthetic operation, which was largely alleviated by only 7% blue. Quantitatively, leaf responses to an increasing blue light percentage resembled responses associated with an increase in irradiance. Next, the wavelength d

Numerous attempts have been made to construct the controlled ecological life support systems (CELSS). The system will be a unique tool for researches such as test beds for the global change problem, the solutions for a zero-emission society and the large-scale life support system in outer space. The morphogenesis of plants in the system may be affected by the environmental change derived from the scale-down in ecological system. However, if the morphogenesis of plants is made clear, the high efficiency and intentional agriculture system will be put into practice. The purpose of this report is to elucidate the photomorphogenesis of plants under the variety of irradiation conditions. The experimental results showed that the changes in irradiation period had a dramatic effect on the germination, the differentiation and the growth of plants. In the 12-hours cycle irradiation which was composed of 6 hours-bright and 6-hours dark, the growth was promoted, although the germination of peas was restricted. Mechanisms based on phytochrome, photosynthesis, circadian rhythm and source-sink relation were proposed to explain these behaviour.

The transcriptional regulator CONSTANS (CO) promotes flowering of Arabidopsis under long summer days (LDs) but not under short winter days (SDs). Post-translational regulation of CO is crucial for this response by stabilizing the protein at the end of a LD, whereas promoting its degradation throughout the night under LD and SD. We show that mutations in CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a component of a ubiquitin ligase, cause extreme early flowering under SDs, and that this is largely dependent on CO activity. Furthermore, transcription of the CO target gene FT is increased in cop1 mutants and decreased in plants overexpressing COP1 in phloem companion cells. COP1 and CO interact in vivo and in vitro through the C-terminal region of CO. COP1 promotes CO degradation mainly in the dark, so that in cop1 mutants CO protein but not CO mRNA abundance is dramatically increased during the night. However, in the morning CO degradation occurs independently of COP1 by a phytochrome B-dependent mechanism. Thus, COP1 contributes to day length perception by reducing the abundance of CO during the night and thereby delaying flowering under SDs.

COP10 is a ubiquitin-conjugating enzyme variant (UEV), which is thought to act together with COP1, DET1, and the COP9 signalosome (CSN) in Arabidopsis to repress photomorphogenesis. Here, we demonstrate that COP10 interacts with ubiquitin-conjugating enzymes (E2s) in vivo, and can enhance their activity in vitro, an activity distinct from previous characterized UEVs such as MMS2 and UEV1. Furthermore, we show that COP10 forms a complex with UV-damaged DNA-binding protein la (DDBla) and de-etiolated 1 (DET1), and physically interacts with COP1 and the CSN. Purified CDD (COP10, DDB1, DET1) complex also shows enhancement of E2 activity (UEA) similar to that observed with COP10 itself. Our data suggests that COP10, along with COP1 and the CSN, promotes the degradation of positive regulators of photomorphogenesis, such as the transcription factor HY5, via the ubiquitin/26S proteasome system. Thus, the CDD complex may act as a ubiquitylation-promoting factor to regulate photomorphogenesis.

[no abstract]

All developmental transitions throughout the life cycle of a plant are influenced by light. In Arabidopsis, multiple photoreceptors including the UV-A/blue-sensing cryptochromes (cry1-2) and the red/far-red responsive phytochromes (phyA-E) monitor the ambient light conditions [1 and 2]. Light-regulated protein stability is a major control point of photomorphogenesis [3]. The ubiquitin E3 ligase COP1 (nstitutively hotomorphogenic 1) regulates the stability of several light-signaling components [4, 5 and 6]. HFR1 (long ypocotyl in ar-ed light) is a putative transcription factor with a bHLH domain acting downstream of both phyA and the cryptochromes [7, 8 and 9]. HFR1 is closely related to PIF1, PIF3, and PIF4 (hytochrome nteracting actor 1, 3 and 4), but in contrast to the latter three, there is no evidence for a direct interaction between HFR1 and the phytochromes [7, 10, 11 and 12]. Here, we show that the protein abundance of HFR1 is tightly controlled by light. HFR1 is an unstable phosphoprotein, particularly in the dark. The proteasome and COP1 are required in vivo to degrade phosphorylated HFR1. In addition, HFR1 can interact with COP1, consistent with the idea of COP1 directly mediating HFR1 degradation. We identify a domain, conserved among several bHLH class proteins involved in light signaling [13 and 14], as a determinant of HFR1 stability. Our physiological experiments indicate that the control of HFR1 protein abundance is important for a normal de-etiolation response

Strydom, S., McMahon, K. M., Kendrick, G. A., Statton, J., & Lavery, P. S. (2017). Short-term responses of posidonia australis to changes in light quality. Frontiers in Plant Science, 8, 2224. doi:10.3389/fpls.2017.02224 Available here.

Strydom, S., McMahon, K., Kendrick, G. A., Statton, J., & Lavery, P. S. (2017). Seagrass Halophila ovalis is affected by light quality across different life history stages. Marine Ecology Progress Series, 572, 103-116. Available here

As sessile organisms, coordination of development and reproduction in a dynamic, and often stressful, environment presents a particular challenge for plants. Rapid processing of internal and external cues by complex signal transduction pathways leads to stimulus-appropriate physiological responses on an organismal scale. In plants, myriad signaling pathways are mediated by calcium (Ca2+) signals, and it is thought that different stimuli elicit unique patterns of Ca2+ influx into cells (termed Ca2+ ‘signatures’) that encode information important for proper physiological responses. Encoding of information in the form of Ca2+ signatures requires that decoding elements be present in cells to direct downstream cellular processes. This role is filled by Ca2+-binding proteins that serve as Ca2+ sensors. Interestingly, plant genomes encode multiple expanded families of Ca2+ sensors not found in animal genomes. Among these, the calmodulin (CaM)-like proteins (CMLs) are represented by a 50 member family in Arabidopsis. On the basis of structural homology, CMLs are predicted to function like conserved CaM, however, little work has been done to address this question. Biochemical characterization of CML39 indicates that it possesses structural properties consistent with function as a Ca2+ sensor. Analysis of transgenic CML39 loss-of-function (cml39) mutants revealed that CML39 is important for proper seedling establishment in the absence of exogenous metabolisable carbon as cml39 seedlings entered a state of developmental arrest shortly after germination. cml39 mutants also exhibited a conditional ‘de-etiolated’ phenotype when grown in complete darkness and exaggerated hypocotyl elongation under a short-day light regime. Genetic data suggest that CML39 functions in signaling pathways downstream of light perception, and this idea is supported by the observation that CML39 iii is expressed in light-sensing tissues, and that subunit 5 of the COP9 signalosome, a protein critical for, Thesis (Ph.D, Biology) -- Queen's University, 2013-05-29 18:16:25.769

The many advantages of light-emitting diode (LED) grow lamps in terms of programmability and energy efficiency make them an attractive replacement for old lighting systems. However, when replacing conventional broad-waveband ‘white’ lighting with narrow-waveband LED lighting it is important to ensure that the system is able to produce plants of an equal or higher quality and yield. In order to choose suitable light ‘recipes’, i.e. combinations of wavelengths for optimal plant growth, we must first understand how light quality affects plant growth and development. The following work explores the role of each part of the light spectrum, both in natural sunlight in canopy environments in the field and glasshouse, and in an artificial light environment in controlled environment growth rooms. It was determined that, blue, green, red and far-red wavebands are all instrumental in the provision of positional signals to the leaf which enable optimisation of plant physiology to light conditions, especially in the canopy environment. A new hypothesis for the role of the blue:green light ratio in whole-canopy water use efficiency is presented. Wavelength-specific effects were observed in hypocotyl elongation, leaf expansion, photosynthetic stoichiometry and absorption of different wavelengths, root architecture, photosynthetic capacity, whole-plant morphology (in terms of biomass partitioning between leaves, stems and roots) and fresh weight yield of stems and leaves. In the glasshouse, it was determined that monochromatic red LED lighting is a suitable alternative for conventional high-pressure sodium light, as it boosted leaf photosynthetic capacity as well as leaf area, fresh and dry weight yield, and was the most efficient light source in terms of ‘crop per watt’. Finally, further applications of the work such as those for commercial horticulture and farming in closed plant production systems are presented, and it is concluded that LED lighting is likely to have a crucial r