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Copyright of Revista Colombiana de Ciencias Hortícolas is the property of Revista Colombiana de Ciencias Horticolas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: The plant-growth-promoting rhizobacterium Tsukamurella tyrosinosolvens is a rare strain of actinomycete, in order to recognize and expand the ecological functions of rare actinomycetes. Methods: In this experiment, we studied the effect of Tsukamurella tyrosinosolvens P9 on the drought resistance of peanut by inoculating peanut seedlings in pots and measuring the growth and physiological indicators of peanut under drought stress and re-watering conditions. Results: The results showed that during drought stress, the relative water content of the soil and leaves, chlorophyll content, and stomatal length, width, and aperture were significantly decreased while the levels of malondialdehyde (MDA), H2O2 and stomatal density were significantly increased. Peanut growth was also inhibited. However, inoculation with the P9 strain significantly promoted the growth of peanut under drought stress as plant height, fresh weight, root length and root weight were significantly higher compared with the uninoculated drought stress group. In addition, in P9-inoculated plants, the water and chlorophyll contents were significantly higher and the activities of the antioxidant enzymes CAT and SOD were significantly increased (except during the six days of drought treatment). While the stomatal length, width, and aperture were improved, the levels of MDA and H2O2 were significantly decreased. NBT staining showed that inoculation with P9 reduced O2− accumulation under stress. After re-watering, the physiological indexes of inoculated plants recovered more quickly and grew better. Conclusions: The results showed that T. tyrosinosolvens P9 enhanced drought resistance and improves peanut growth by increasing leaf water content, increasing photosynthesis, regulating stomatal closure, and improving antioxidant enzyme activity. [ABSTRACT FROM AUTHOR]

Drought stress is one of the major environmental obstacles that limit the production and development of apples (Malus domestica Borkh.). The role of melatonin is well known in the protection of plants under environmental stresses. In this study, we investigated the effect of melatonin on apple rootstock M. hupehensis Rehd under drought stress. The results showed that drought inhibited the growth of M. hupehensis and dramatically reduced root surface area, root volume, the number of tips and forks, and root diameter. Drought-induced growth inhibition was significantly decreased by adding melatonin. Net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), transpiration rate (Tr), were markedly reduced under drought stress. However, the application of melatonin could mitigate the damage to the photosynthetic apparatus and increase the quantum yield of PSII photochemistry. Additionally, generation of hydrogen peroxide (H2O2) and superoxide radicals (O2 •-) sharply increased in apple leaves after 4 days under drought stress, and the accumulation of electrolyte leakage (EL) represented oxidative stress, while by applying melatonin under drought stress, the generation of O2 •- and H2O2 were significantly reduced and protected the membrane from drought damages. These results suggest that the adverse effects of drought can be minimized by applying melatonin to apples. [ABSTRACT FROM AUTHOR]

Tea plants are sensitive to soil moisture deficit, with the level of soil water being a critical factor affecting their growth and quality. Arbuscular mycorrhizal fungi (AMF) can improve water and nutrient absorption, but it is not clear whether AMF can improve the photosynthetic characteristics of tea plants. A potted study was conducted to determine the effects of Claroideoglomus etunicatum on plant growth, leaf water status, pigment content, gas exchange, and chlorophyll fluorescence parameters in Camellia sinensis cv. Fuding Dabaicha under well-watered (WW) and drought stress (DS) conditions. Root mycorrhizal colonization and soil hyphal length were significantly reduced by the eightweek DS treatment. AMF inoculation displayed a significant increase in shoot and root biomass production. The relative water content, leaf water potential, nitrogen balance index, pigment content, maximum photometric effect (Fv/Fm, QY_max), and steady-state photometric effect Y (II) (QY_Lss) decreased dramatically, while the leaf water saturation deficit and steady-state non-photochemical fluorescence quenching (NPQ_Lss) generally increased under DS conditions. Mycorrhizal treatment induced significantly higher relative water content, leaf water potential, nitrogen balance index, pigment (chlorophyll, flavonoid, and anthocyanin) content, net photosynthesis rate, transpiration rate, stomatal conductance, intercellular CO2 concentration, QY_max, and QY_Lss; however, it resulted in a lower leaf water saturation deficit and NPQ_Lss under both WW and DS conditions, as compared with nonmycorrhizal plants. These results imply that AMF promoted tea plant growth and alleviated negative effects of DS by promoting gas exchange, regulating the water status of leaves, and regulating photosynthetic parameters. [ABSTRACT FROM AUTHOR]

The Brazilian Cerrado is the second largest Brazilian biome. In recent decades, a reduction in rainfall has indicated an extension of the dry season. Among the many native species of the Cerrado of the Annonaceae family and used in folk medicine, Annona crassiflora Mart. has fruits of high nutritional value and its by-products are sources of bioactive compounds, such as alkaloids. The aim of the study was to investigate how water stress impacts the production of alkaloids. The study was carried out in a nursery, and the knowledge was flood, field capacity and drought. Gas exchange, chlorophyll a fluorescence, antioxidant enzymes, total soluble sugars, starch, reducing sugars, sucrose, total alkaloids and liriodenine were analyzed. We observed that plants subjected to drought had an increase in the production of total alkaloids and liriodenine, without a reduction in photosynthetic metabolism. Plants kept under drought and flood conditions dissipated higher peroxidase activity, while catalase was higher in flooded plants. Starch showed the highest concentration in flooding plants without differing from drought plants; the lowest trehalose concentrations were found in both drought and flooding plants. The drought stimulated the synthesis of total alkaloids and liriodenine without reducing the primary metabolism, which suggests adaptation to Cerrado conditions. [ABSTRACT FROM AUTHOR]

Vegetative ground covers are commonly used in urban, tropical roadside gardens. Such landscaping ground covers usually encounter extreme water-deficits and high temperatures from vehicles and urban infrastructures. However, information about the plant species that are appropriate for low maintenance gardens is not available, especially in tropical areas. This study aimed to investigate potential indicators for evaluating plant tolerance to water-deficit situations. A non-irrigated rooftop model was used to test 25 commercial ground cover species in a greenhouse at Mahidol University, Nakhon Pathom Province, Thailand. Each of these 25 species was potted and subjected to one of two conditions: with or without irrigation for 7 days. Physiological responses relevant to plant endurance during water-deficits were monitored, including changes in leaf relative water content (RWC), percent stomatal opening, leaf surface temperature, leaf total chlorophyll content, leaf greenness, maximum quantum yield, and light quantum yield. Moreover, an additional indicator of landscape utility was evaluated, where each species was judged by trained panelists for their esthetic appeal. Diverse responses were observed based on the type of physiological parameter measured, plant species, and duration of drought conditions. Water withdrawal for three days was deemed an appropriate time to determine plant tolerance to water-deficit conditions, as signs of stress were clearly observed in three parameters, i.e., changes in leaf RWC, percent stomatal opening, and esthetic score. Lastly, cluster analysis revealed that seven plant species were appropriate for tropical, urban ground covers, as they had high endurance under water-deficit conditions, namely, Allium schoenoprasum, Liriope muscari, Aloe sp., Sedum x rubrotinctum, Alternanthera ficoidea, Pilea libanensis and Plectranthus scutellarioides. [ABSTRACT FROM AUTHOR]

Water deficit is a major worldwide constraint to common bean (Phaseolus vulgaris L.) production, being photosynthesis one of the most affected physiological processes. To gain insights into the genetic basis of the photosynthetic response of common bean under water-limited conditions, a collection of 158 Portuguese accessions was grown under both well-watered and water-deficit regimes. Leaf gas-exchange parameters were measured and photosynthetic pigments quantified. The same collection was genotyped using SNP arrays, and SNP-trait associations tested considering a linear mixed model accounting for the genetic relatedness among accessions. A total of 133 SNP-trait associations were identified for net CO2 assimilation rate, transpiration rate, stomatal conductance, and chlorophylls a and b, carotenes, and xanthophyll contents. Ninety of these associations were detected under water-deficit and 43 under well-watered conditions, with only two associations common to both treatments. Identified candidate genes revealed that stomatal regulation, protein translocation across membranes, redox mechanisms, hormone, and osmotic stress signaling were the most relevant processes involved in common bean response to water-limited conditions. These candidates are now preferential targets for common bean water-deficit-tolerance breeding. Additionally, new sources of water-deficit tolerance of Andean, Mesoamerican, and admixed origin were detected as accessions valuable for breeding, and not yet explored. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Forestry Society of Croatia / Sumarski List Hrvatskoga Sumarskoga Drustva is the property of Forestry Society of Croatia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigated the physiological and ecological changes in P. sepium Bunge and elucidated the physiological regulatory mechanisms underlying the adaptation of P. sepium to drought stress in shell sand. Drought stress led to a significant decrease in the net photosynthesis rate (Pn) and respiration rate of leaves and a decrease in low-intensity light-use efficiency (LUE) and light ecological amplitude. An increase in drought stress led to a considerable decrease in the photosynthetic electron transport rate in the P. sepium leaves and a significant increase in the amount of light energy dissipated as heat. In addition, the photosynthesis process suffered from severe photoinhibition. P. sepium plants counteracted the effects of drought stress primarily by increasing their peroxidase (POD) activity and by regulating membrane lipid peroxidation by secreting greater numbers of osmotic adjustment substances (proline (Pro) and soluble sugars (Ss)) and malondialdehyde (MDA). As drought stress increased, both the stem sap flow rate and the cumulative sap flow of P. sepium decreased considerably. P. sepium Bunge adapts to drought stress through interregulatory activity between photosynthesis, water-related physiological activities, and physiological and biochemical processes, and this species exhibits relatively high adaptive plasticity to drought. [ABSTRACT FROM AUTHOR]

The protective role of melatonin in plants against various abiotic stresses have been widely demonstrated, but poorly explored in organ-specific responses and the transmission of melatonin signals across organs. In this study, the effects of melatonin with the root-irrigation method and the leaf-spraying method on the antioxidant system and photosynthetic machinery in maize seedlings under drought stress were investigated. The results showed that drought stress led to the rise in reactive oxygen species (ROS), severe cell death, and degradation of D1 protein, which were mitigated by the melatonin application. The application of melatonin improved the photosynthetic activities and alleviated the oxidative damages of maize seedlings under the drought stress. Compared with the leaf-spraying method, the root-irrigation method was more effective on enhancing drought tolerance. Moreover, maize seedlings made organ-specific physiological responses to the drought stress, and the physiological effects of melatonin varied with the dosage, application methods and plant organs. The signals of exogenous melatonin received by roots could affect the stress responses of leaves, and the melatonin signals perceived by leaves also led to changes in physiological metabolisms in roots under the stress. Consequently, the whole seedlings coordinated the different parts and made a systemic acclimation against the drought stress. Melatonin as a protective agent against abiotic stresses has a potential application prospect in the agricultural industry. [ABSTRACT FROM AUTHOR]

Highlights • The modulation of elevated CO 2 on stomatal response to progressive drought was studied in tomato plants. • Elevated CO 2 retarded the response of photosynthesis and stomatal conductance to soil water deficits. • The responsiveness of stomatal conductance to ABA was unaffected by CO 2 environment. • Elevated CO 2 enhanced both water use efficiency and nitrogen use efficiency in tomato plants. Abstract The objective of this study was to investigate the response of leaf gas exchange of tomato plant to progressive drought stress under ambient (a [CO 2 ], 400 ppm) and elevated (e [CO 2 ], 800 ppm) atmospheric CO 2 concentration. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. The results showed that stomatal conductance (g s) and transpiration rate (T r) were significantly lower while the net photosynthetic rate (A n) was significantly higher in plants grown under e [CO 2 ] than those under a [CO 2 ] at onset of drought stress. Along with soil drying, the FTSW thresholds at which g s and A n started to decrease were significantly lower in plants grown under e [CO 2 ] as compared to plants grown under a [CO 2 ]. The intrinsic water use efficiency and instantaneous water use efficiency of plants grown under e [CO 2 ] was significantly higher than those under a [CO 2 ]. Under e [CO 2 ], the drought-stressed plants had greater leaf area, dry matter and water use efficiency than those grown under a [CO 2 ]. e [CO 2 ] notably enhanced shoot C concentration while decreased shoot N concentration hereby increased the C:N ratio. With the decrease of FTSW, the concentration of abscisic acid in leaf ([ABA] leaf) and xylem sap ([ABA] xylem) increased exponentially. When FTSW > 0.2, under both CO 2 environments, g s decreased linearly with increasing [ABA] leaf and [ABA] xylem ; and similar slopes but different intercepts were noticed for the regression lines, indicating that the responsiveness of g s to ABA was unaffected by CO 2. In conclusion, CO 2 elevation retarded the response of leaf gas exchange to progressive soil drying in tomato plants. This result provides novel knowledge for more precise prediction of plant response to drought stress in a future CO 2 -enriched environment. [ABSTRACT FROM AUTHOR]

Highlights • Photosynthetic enzymes are regulated spatially and temporally by epigenetic mechanisms. • Light and drought stress disturb different types of photosynthesis. • miRNAs and their functions is different among plant species. Abstract Without photosynthesis, life on earth as we know it would be impossible. Advances in our understanding of how light harvesting and carbon fixation work have traditionally been driven by biochemical and molecular approaches with the goal of increasing crop yield. However, environmental challenges are putting the survival of many plants at risk due to photosynthetic inbalance. Epigenetic regulation has only recently been recognized as an important player in the response to changes in key environmental conditions such as light, temperature and drought, and while there has been scattered research on the topic, it has not yet been collated into a review. Here we focus on epigenetics' affect on photosynthesis-related carbon fixation pathways and identify important directions for future research. For instance, during the perception of light, epigenetic regulation mediates a complex and flexible series of events, including histone acetylation and DNA demethylation, to promote expression of several genes involved in carbon fixation, such as RuBisCO and PEPC in C 3 and C 4 plants, respectively. On the other hand, the crucial role of deacetylases of histones HD1 and HDA15 and the possible participation of miRNAs during light/dark signaling and light harvesting, respectively, reveal an unexplored connection between light signaling and epigenetic regulation during photosynthesis. In the present review, we highlight how euchromatin configuration helps in the acquisition of drought tolerance and efficient stomata conductance. Therefore, we suggest that several drought-sensitive crops could be improved with the use of miRNA to optimize photosynthetic stomata conductance and gas exchange. [ABSTRACT FROM AUTHOR]

Isoprene is emitted by many plants and is thought to function as an antioxidant under stressful conditions. However, the detailed regulatory mechanism of isoprene emission in relation to the antioxidant system remains unclear. Therefore, in this study, we explored the molecular regulatory mechanism of isoprene emission under short-term drought stress in the tropical tree Ficus septica Burm.f. We found that the soil moisture content gradually decreased from 55% on Day 1 (D1) to 23% (wilting point) on D5 after withholding water for 4 days and then returning to the initial level following re-watering on D6. On D5, drought-stressed plants had more than twofold higher isoprene emission and 90.6% lower photosynthesis rates, 99.5% lower stomatal conductance and 82.3% lower transpiration rates than well-watered control plants. It was also estimated that the isoprene concentration inside the leaf greatly increased on D5 due to the increased isoprene emission rate and reduced stomatal conductance. Among the traits related to the 2-C-methyl- d -erythritol-4-phosphate (MEP) pathway, which is responsible for isoprene biosynthesis, the isoprene synthase (IspS) protein level was positively correlated with the isoprene emission rate in stressed plants. The transcripts of the antioxidant genes peroxidase 2 (POD2), POD4, copper-zinc superoxide dismutase 2 (Cu-ZnSOD2) and manganese superoxide dismutase 1 (Mn-SOD1) also increased during the drying period, while those of ascorbate peroxidase 1 (APX1) decreased. However, there was only a weak correlation between isoprene emission and antioxidant enzyme gene expression, indicating that the regulation of isoprene biosynthesis is not directly linked to the antioxidant defense network in drought-stressed F. septica. These findings suggest that the post-transcriptional regulation of IspS led to the observed change in isoprene emission rate, which enhanced the quenching of reactive oxygen species (ROS) and, in combination with the increased antioxidant enzyme activity, conferred tolerance to drought stress in this species. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New insights regarding the mechanisms and processes involved in S. dolomitica drought adaptation are provided. • Moderate drought decreased growth, leaf water potential and stomatal conductance, while increased deyhdrin gene expression. • Severe drought decreased net photosynthesis and transpiration rate. • Drought increased sesquiterpene production by modulating gene expression of key enzymes of terpenoid biosynthesis. • Moderate drought can ameliorate secondary metabolites production and water-management practices in S. dolomitica. Abstract Sage is an important medicinal and aromatic plant. While Salvia officinalis and S. miltiorrhiza have been widely studied, little information regarding S. dolomitica exists, although it has recently attracted attention due to its anti-plasmodial and anti-inflammatory properties. This study investigated the performance and metabolic profile of this species in response to two drought treatments (moderate or severe) relative to well-watered control plants. Changes in growth and ecophysiological traits, as well as in bioactive and volatile compounds and essential oil production were determined. Given that terpenoids are the most representative class of secondary metabolites, the gene expression of key enzymes of terpenoid biosynthesis was also investigated. Moderate drought stimulated a decline in leaf water potential, growth and stomatal conductance, as well as an increase in deyhdrin expression. Serious stress symptoms occurred only in severe drought-stressed plants, where a decline in net photosynthesis and transpiration and an increase in endogenous abscisic acid was observed. Both drought stress conditions led to modulate the expression of some genes involved in biogenic volatile organic compound and essential oil biosynthesis and metabolic profile. In particular, drought induced an increase in sesquiterpene production, a class of terpenoids that is important in the food, cosmetics, and pharmaceutical industries. Thus, controlled drought, in addition to water savings during cultivation, can be applied to improve the production of secondary metabolites in S. dolomitica. [ABSTRACT FROM AUTHOR]

Highlights • The anti-transpirant Vapor Gard has a beneficial, albeit temporary, effect in pea. • Reduced transpiration causes an early inhibition of symbiotic nitrogen fixation. • Regulation of nitrogen fixation is not associated with amino acid accumulation. Abstract Stomatal closure is one of the first plant responses under a water deficit situation. This leads to a decline in transpiration but also in the plant photosynthetic activity. Legume plants grown under symbiosis with rhizobium bacteria present an inhibition of nitrogen fixation that has been shown to occur even before this of photosynthesis. One of the hypotheses to explain this rapid inhibition is the accumulation of nitrogen (N) compounds in nodules due to reduced transpiration, which would provoke the N-feedback inhibition of nitrogenase activity. The current work analyzes the effects of changes in transpiration rates in the regulation of nitrogen fixation through the application of the anti-transpirant Vapor Gard (VG) to pea (Pisum sativum L.) plants subjected to a progressive water deficit. VG produced a rapid inhibition of nitrogen fixation upon application. This inhibition, however, did not coincide with the accumulation of either amino acids or soluble carbohydrates observed at later drought stages in nodules. Results show that the application of VG has a beneficial, albeit temporary, effect in both maintaining the plant water status and apparent nitrogenase activity of nodulated pea plants under water-deficit conditions. [ABSTRACT FROM AUTHOR]

Highlights • Drought and saline water caused permanent damages to olive leaf activity. • Water status recovery after a severe drought. • physiological performance of olive not fully recovered after re-watering. • Saline water irrigation reduced drought impact on olive tree growth. • Young leaves have the same photosynthetic capacity indecently of the stress. Abstract Effects of drought and salinity on water status, growth and physiological activity of olive can be temporary or permanent and may impact olive production sustainability, especially in southern Mediterranean areas. Tunisia has a Mediterranean climate with high temperatures and low summer rainfall. Thus water stress problems are likely to be more severe for cultivated olive trees. In addition, the reduction in the availability of good quality irrigation water will increase the use of saline water. Olive trees are able to tolerate low soil water availability and quality and develop physiological adaptations to cope with water and salt stress. However, these adaptation strategies are limited and permanent damages can be observed. The permanent effects caused to olive leaves due to drought, and the capacity of irrigation with saline water to avoid these impacts is not well known. The aim of this work was to compare olive leaves performance after a severe drought with, and without, irrigation and to assess recovering capacities after a rainy period. Moreover, irrigation water quality effects were also evaluated. The results showed that, photosynthetic rate was very low for rainfed plants, during drought, as compared to irrigated ones. After re-watering, rainfed trees photosynthetic rate was only 55% of that of trees irrigated with fresh water. Irrigation with saline water (EC = 7.5 dS m−1) reduced drought impact by increasing photosynthesis by 55% but remained lower than that of fresh water by 23%. Thus olive leaves were unable to recover their whole photosynthetic capacity after being exposed to severe water or salt stress. Furthermore, young leaves had the same photosynthetic capacity at the beginning. This indicated that olive leaves lost permanently half of their photosynthetic activity during to drought without irrigation. The use of saline water reduced this gap to 23% as compared to fresh water. [ABSTRACT FROM AUTHOR]

Highlights • K step appeared in OJIP transient and ET 0 /RC, ET 0 /CS 0 , φE 0 of rice seedlings were decreased under drought stress. • Si treatment delayed chlorophyll-protein complexes degradation of rice seedlings under stress. • Si treatment altered the thylakoid protein components under drought stress. • Si treatment maintained photosynthetic performance by improving light energy absorption and transformation. Abstract For revealing the internal mitigation mechanism of silicon to drought stress, a super high-yield hybrid rice LYP9 was employed to study the change of photosynthetic fluorescence, structure and composition of thylakoid membrane as well as its physiological property by polyethylene glycol (PEG) and silicon (Si) treatment. Results showed that K step appeared in OJIP transient and ET 0 /RC, ET 0 /CS 0 , φE 0 of rice seedlings were decreased under drought stress, while these parameters were increased by applying silicon. We found that silicon application could relieve the degradation of membrane protein complexes under drought condition, such as supercomplexes, PSI core binding LHCI, PSI core, F 1 -ATPase binding Cyt b 6 /f complex, PSII core, trimeric LHCII and monomeric LHCII. Thylakoid membranes proteins were further detected by BN-SDS-PAGE, 20 differential protein spots between PEG treatment and PEG treatment applying with silicon were identified. These alterations were involved in light harvesting, stability of PS I, function of PS II reaction centers, electron transport, PS II core antenna content, and consequent synthesis of ATP. Our results indicated that Si treatment might play roles in absorption, transformation and transfer of light energy by optimizing the thylakoid membrane protein components in rice seedlings under drought stress observed by BN-PAGE and BN-SDS-PAGE. [ABSTRACT FROM AUTHOR]

Highlights • PF, DF and P700 revealed complementary information on drought-induced changes. • Drought impaired OEC, PSII RCs and PSI acceptor side in maize photosynthetic chain. • Drought decreased maize photosynthetic forward, backward and cyclic electron flows. • Cyclic electron flows might play an important role in maize response to drought. Abstract The effect of drought on the prompt chlorophyll a fluorescence (PF) transient (OJIP), delayed chlorophyll a fluorescence (DF), modulated 820-nm reflection (MR), energy conversion efficiencies in photosystems (PS) I and II, and cyclic electron flow (CEF) activity in two maize hybrids with contrasting drought tolerance was investigated. Our aim was to identify the target site of drought stress on the photosynthetic electron transport chain and investigate the relevance of the CEF pathway to the drought tolerance of maize plants. The OJIP analysis showed that drought stress, depending on its duration, decreased F P , increased F J , and induced a pronounced K-band and a positive L-band. Moreover, OJIP parameters, including PI ABS , RC/CS O , TR O /ABS, and ET O /TR O , were significantly reduced. The DF analysis showed that the values of I 1 and I 2 in the induction curve and L 1 and L 2 derived from the decay curve decreased progressively with the duration of drought stress. The MR analysis showed that drought stress inactivated both the fast decrease and slow increase phases of the MR transient, resulting in a gradual decrease in both V PSI and V PSII-PSI. The energy conversion analysis showed that drought stress decreased the PSI photochemical quantum yield Y(I) and PSII photochemical quantum yield Y(II). Compared to the tolerant hybrid, the drought-induced changes in the sensitive hybrid were stronger and appeared at an earlier treatment stage. The CEF activity analysis showed that the CEF pathway under drought stress operated for a longer time in the tolerant hybrid than that in the sensitive hybrid. The above results indicate that drought stress damaged the donor and acceptor sides of PSII, the PSII reaction center and the acceptor side of PSI and decreased the efficiency of both PSI and PSII and the capacity of electron transfer. The CEF pathway might play an important role in the tolerance of the maize photosynthetic electron transport chain to drought stress. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Proteomics has coupled with morpho-physiology of drought sensitive and resistant parents to define the resistant traits of their progenies. • DAPs in leaf of parents and progeny F6, shed light on the inheritance of the molecular characters that lead to resistance. • The experimental design with proteomic approach might build a complimentary method for future marker-assisted selection of drought resistance. Abstract Comparative physiological and proteomic analyses of two wheat cultivars Arg (resistant to drought), Arta (sensitive to drought) and four F6 lines (B1, B2, W1, W2) derived from their crossbreed lead us to discriminate the Arg, B1 and B2 lines to be resistant toward strong leaf water deficit. Proteins belonging to carbon metabolism, photosynthesis and detoxification/defense showed the major change. Tolerant Arg showed the accumulation of stress-responsive proteins under drought stress higher than in sensitive Arta. The high level of Cu/Zn superoxide dismutase, and two chloroplastic encoded enzymes indicate that their accumulation might improve stress resistance. Morphological and physiological traits of B1 and B2 confirmed that these lines are tolerant to drought stress. Proline and MDA contents are higher and lower, respectively, in these two lines than in other ones. This act synergistically with the modulation of primary metabolisms and protection against dehydration and oxidative damage resulting in the improvements of survival of the seedlings, greater vegetative vigor and productive capacity that also exceeds that of the tolerant Arg parental line. For all these evidences, the B1 and B2 progenies could be selected as the best lines in the future cultivation trials for wheat breeding under moderate and severe drought conditions. [ABSTRACT FROM AUTHOR]

Highlights • This is the first report of Withania coagulans response to G × E interaction. • Distance between stress time and photosynthesis indices measurements is important. • Values for F v / F m in Fanuj, F 0 and ФPSII decreased with increasing stress severity. • Photosynthesis rate declined and leaf greenness increased with the onset of drought. • According to results, W. coagulans can be called "Xerophytes Camel". Abstract Withania coagulans is one of the most important medicinal species of the Solanaceae which has pharmacological properties for future research in drug development. Photosynthesis and morphological parameters in response to drought of this species have not been investigated as yet, though the issue is of interest. The factorial combination of four water deficit stress (20% (un-stressed control), 30%, 40% and 50% of FC depletion) and four landraces of W. coagulans (Fanuj, Khash, Saravan and Sarbaz) were laid out in a randomized complete design in a phytotron over the course of 180 days. The first, second, third and fourth samplings were performed every 45 day after imposing the treatments (DAT). The results demonstrated that increase in the water deficit stress levels, decreased minimal fluorescence (F 0), leaf greenness, photosynthesis rate, plant height, leaf area, dry weight and quantum yield of PSII photochemistry)Ф PSII (in all landraces and maximum photochemical efficiency of PSII (Fv/Fm) in Fanuj, but increased non-photochemical quenching) NPQ (and Fv/Fm in Saravan and Sarbaz landraces. The W. coagulans landraces such as Fanuj with the highest vector loadings of Ф PSII at 135 and 180 DAT and F v /F m at 45 DAT and Sarbaz with the highest vector loading of F 0 at 45 DAT were found suitable for unstressed and severe stress conditions, respectively. Among the chlorophyll fluorescence and morphological parameters, total dry weight had the significant positive correlations with plant height, leaf area and F 0 at 45 DAT. Thus, this study indicated chlorophyll florescence should be measured at different phases and future studies should focus on the sensitivity of these parameters to detect potential times among subjects of different stresses. These parameters are easy, cheap, efficient and reliable physiological characteristics which can be used to guide the breeding of new resistant genotypes. According to results, W. coagulans can be called "Xerophytes Camel". [ABSTRACT FROM AUTHOR]

Abstract Apocynum venetum is an eco-economic plant species with high adaptability to saline and arid environments. Our previous work has found that A. venetum could absorb large amount of Na+ and maintain high K+ level under saline conditions. To investigate whether K+ and Na+ could simultaneously enhance drought resistance in A. venetum , seedlings were exposed to osmotic stress (−0.2 MPa) in the presence or absence of additional 25 mM NaCl under low (0.01 mM) and normal (2.5 mM) K+ supplying conditions, respectively. The results showed that A. venetum should be considered as a typical K+-efficient species since its growth was unimpaired and possessed a strong K+ uptake and prominent K+ utilization efficiency under K+ deficiency condition. Leaf K+ concentration remained stable or was even significantly increased under osmotic stress in the presence or absence of NaCl, compared with that under control condition, regardless of whether the K+ supply was sufficient or not, and the contribution of K+ to leaf osmotic potential consistently exceeded 37%, indicating K+ is the uppermost contributor to osmotic adjustment of A. venetum. Under osmotic stress, the addition of 25 mM NaCl significantly increase Na+ accumulation in leaves and the contribution of Na+ to osmotic adjustment, thus improving the relative water content, concomitantly, promoting the photosynthetic activity resulting in an enhancement of overall plant growth. These findings suggested that, K+ and Na+ simultaneously play crucial roles in the osmotic adjustment and the maintenance of water status and photosynthetic activity, which is beneficial for A. venetum to cope with drought stress. Highlights • Apocynum venetum is a typical K+-efficient desert plant with high K+-uptake and -utilization efficiencies. • Large accumulation of K+ to improve osmotic adjustment is vital for A. venetum to cope with osmotic stress. • Moderate NaCl could substantially enhance leaf photosynthesis and hydration of A. venetum under osmotic stress. [ABSTRACT FROM AUTHOR]

Global climate change is expected to increase drought duration and intensity in certain regions while increasing rainfall in others. The quantitative consequences of increased drought for ecosystems are not easy to predict. Process-based models must be informed by experiments to determine the resilience of plants and ecosystems from different climates. Here, we demonstrate what and how experimentally derived quantitative information can improve the representation of stomatal and non-stomatal photosynthetic responses to drought in large-scale vegetation models. In particular, we review literature on the answers to four key questions: (1) Which photosynthetic processes are affected under short-term drought? (2) How do the stomatal and non-stomatal responses to short-term drought vary among species originating from different hydro-climates? (3) Do plants acclimate to prolonged water stress, and do mesic and xeric species differ in their degree of acclimation? (4) Does inclusion of experimentally based plant functional type specific stomatal and non-stomatal response functions to drought help Land Surface Models to reproduce key features of ecosystem responses to drought? We highlighted the need for evaluating model representations of the fundamental eco-physiological processes under drought. Taking differential drought sensitivity of different vegetation into account is necessary for Land Surface Models to accurately model drought responses, or the drought impacts on vegetation in drier environments may be over-estimated. [ABSTRACT FROM AUTHOR]

Thioredoxins (Trxs) modulate metabolic responses during stress conditions; however, the mechanisms governing the responses of plants subjected to multiple drought events and the role of Trxs under these conditions are not well understood. Here we explored the significance of the mitochondrial Trx system in Arabidopsis following exposure to single and repeated drought events. We analyzed the previously characterized NADPH-dependent Trx reductase A and B double mutant (ntra ntrb) and two independent mitochondrial thioredoxin o1 (trxo1) mutant lines. Following similar reductions in relative water content (∼50%), Trx mutants subjected to two drought cycles displayed a significantly higher maximum quantum efficiency (F v/ F m) and were less sensitive to drought than their wild-type counterparts and than all genotypes subjected to a single drought event. Trx mutant plants displayed a faster recovery after two cycles of drought, as observed by the higher accumulation of secondary metabolites and higher stomatal conductance. Our results indicate that plants exposed to multiple drought cycles are able to modulate their subsequent metabolic and physiological response, suggesting the occurrence of an exquisite acclimation in stressed Arabidopsis plants. Moreover, this differential acclimation involves the participation of a set of metabolic changes as well as redox poise alteration following stress recovery. [ABSTRACT FROM AUTHOR]

Highlights • PSII photochemistry efficiency were monitored over an entire leaf-life span. • PSII photochemistry dropped only with severe drought episode. • Photoprotection occurred through heat dissipation strategies with drought episode. • Rewatering did not enhance the photoprotection with leaf aging. Abstract Plant growth and photosynthesis in response to water status have been extensively investigated. However, elucidating the photosynthetic process and its indicators under a drought episode and rewatering across the entire leaf lifespan is often neglected. In this experiment, three water treatments were set during two growth seasons: a control treatment, moderate persistent drought (T 1), and severe persistent drought (T 2). Maize leaf chlorophyll fluorescence emission was analyzed to determine the regulative responses of the photosynthetic potentials and photosystem II (PSII) photochemistry process to drought and rewatering in situ. A severe drought episode during the peak vegetative growth stage resulted in decreases in chlorophyll content, the maximal efficiency of PSII photochemistry (F v / F m), and photochemical quenching, but increases in non-photochemical quenching and the yield for dissipation by downregulation. Rewatering only restored partial PSII functions in plants that had undergone historical drought episodes. An analysis of non-photochemical pathways of thermal dissipation indicates that regulative photoprotection of the photosystem apparatus may occur through heat dissipation when an effect of severe drought episode appeared on a young leaf; however, rewatering did not enhance photoprotection with leaf aging. Compared to the control treatment, the yield of T 1 and T 2 decreased by 25.1% and 27.1% in 2015, and 26.4% and 54.3% in 2016, respectively. The chlorophyll content was significantly and closely correlated with F v / F m (R = 0.65, P < 0.001) and the maximum versus minimum fluorescence yield in the dark-adapted state (F m / F o) (R = 0.72, P < 0.001). Additionally, the two parameters can be suggested to feasibly track chlorophyll content changes and the degree of leaf senescence in responses to a drought episode and its interaction with leaf aging: F m / F o and the relative limitation to photosynthesis (RLP). The current results may provide a profound insight into better understanding the underlying mechanism of photosynthetic potentials and photochemistry efficiency and photoprotection in response to drought episodes and rewatering over the entire leaf lifespan. [ABSTRACT FROM AUTHOR]

To investigate the role of seeds origin in drought tolerance, the response to water deprivation of cork oak seedlings differing in climatic conditions at their geographical origin was compared. Gaâfour is the provenance from the driest site and Feija is the provenance from the wettest site. Net photosynthesis (An), stomatal conductance (gs) and leaf water potential were measured during dehydration. A delayed decrease in leaf water potential is observed after water withholding in Gaâfour as compared to Feija leaves. At the onset of dehydration, An and gs were higher in Feija. After withholding watering, Gaâfour leaves were able to maintain a higher An and gs than Feija leaves. Most likely, drought tolerance in Gaâfour leaves is associated to their lower gs under wellhydrated conditions. The stomatal density (Ds) and specific leaf area (SLA) were not different in well-watered leaves but, leaf hydraulic conductance was lower in Gaâfour leaves when compared to Feija leaves. Our results suggested that lower stomatal and hydraulic conductances of Gaâfour leaves could be involved in bringing about the better resistance to dehydration. [ABSTRACT FROM AUTHOR]

To clarify how the components of the entire photosynthetic electron transport chain in response to drought stress in maize. The activities of photosystem II (PSII), photosystem I (PSI), and the electron transport chain between PSII and PSI of maize were investigated by prompt fluorescence (PF), delayed fluorescence (DF) and 820 nm modulated reflection (MR). Maize (Zea mays L.) plants were subjected to different levels of soil water availability including control, moderate and severe drought stress. A significant decrease in ϕE0, Ψ0 and PIABS was found in maize treated with moderate drought stress. A significant increase in ABS/RC was observed, but there were no significant change in the fast MR phase and the amplitude of DF under moderate drought stress compared to the control. Under severe drought stress, the exchange capacity between QA to QB, reoxidation capacity of plastoquinol, and the oxidation and re-reduction rates of PC and P700 all decreased. These results demonstrated that moderate drought stress reduced the photochemical activity of PSII from QA to PQH2, while the photochemical activity of PSI was unscathed. However, severe drought stress inhibited the entire electron transport chain from the donor side of PSII to PSI-end electron acceptors. In addition, the photochemical activity of PSII is more sensitive to drought stress than PSI. [ABSTRACT FROM AUTHOR]

Abstract The predicted accentuation of drought events highlights the importance of optimize plants capacity to tolerate drought, but also the capacity to recovery from it, especially in species, as olive tree (Olea europaea L.), that grows in particularly susceptible regions. Three different concentrations (10, 100 and 1000 μM) of salicylic acid (SA), a stress signaling phytohormone, was sprayed on 3-year-old potted olive trees subjected to three successive drought and rewatering events. Trees responses to SA application are concentration dependent, being 100 μM the most effective concentration to improve drought tolerance and recovery capacity. During drought events, this effectiveness was achieved by osmolytes accumulation, leaf water status maintenance, reduced photosynthetic systems drought-associated damages, and by optimizing shoot/root ratio. The better plant fitness during drought allowed a fast recovery of the physiological functions upon rewatering and reduced the necessity to invest in extra repair damages, allowing the regrowth. The intense abscisic acid (ABA) signal close to upper epidermis in stressed controls suggests a "memory" of the worst water status displayed by those plants. SA attenuated the limitation of total biomass accumulation imposed by drought, mainly in root system, increased water use efficiency and lead to a higher intense signal of indoleacetic acid (IAA) in leaves during recovery period. In summary, in a suitable concentration, SA demonstrate to be a promising tool to increase drought adaptability of olive trees. [ABSTRACT FROM AUTHOR]

To understand the effects of salt and drought stress factors on the growth, physiological and biochemical responses of cabbage ( Brassica oleracea var. capitata), a greenhouse experiment was conducted with different levels of salinity (S0: tap water, S1: tap water containing extra 75 mM dose of NaCl, and S2: tap water containing extra 150 mM dose of NaCl), irrigation quantity (W0: Full-irrigation, W1: irrigation with 80% of the W0, and W2: irrigation with 60% of the W0), and their combinations. The results showed that antioxidant activity, proline and sucrose contents increased under both salinity and drought stress as well as their combination. Moreover, oxidative damage indicating parameters such as electrical leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H 2 O 2 ) increased as well. Increased level of salinity and drought stress caused a decrease in chlorophyll content (SPAD), leaf relative water content (LRWC), stomatal conductance (g s ), net photosynthetic activity (A n ), intercellular CO 2 content (Ci) and transpiration rate (Tr). We observed that proline and sucrose contents could not stimulate the growth of plant under increased levels of salinity and drought stress. Individual drought and salt stress conditions have negatively affected plant growth including the shoot, root fresh and dry weights when applied separately. On the other hand, the combination of drought and salinity enhanced the adverse effects of each stress factor. [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen (N) deficiency and drought are two key limiting factors for rice production worldwide, but the relationship of drought stress with N homeostasis in rice is rarely advanced. The aim of this study was to dissect the physiological effects of drought stress on rice growth that coupled unbalanced N metabolism.Results: Water-deficient stress (WD) limited stomatal aperture function and activity of Rubisco carboxylase to photosynthesis. The rate of total electron transport (Jt) and the electron to carboxylation (Jc) were considerably decreased, whereas the proportion of e− flow to photorespiration was stimulated by WD, especially at 1600 μmol m−2 s−1 PPFD. Concurrently, the expressions of glycolate oxidase genes (GOX1, GOX5) and glycine decarboxylase complex (GDCH, GDCP and GDCT) were significantly induced in leaves of WD treatment, which led to the accumulation of reactive oxygen species in leaves. With the photosynthetic change, nitrate uptake and reduction were suppressed. Moreover, the enhanced photorespiration generated excess NH3 accumulation in leaves and stimulated the expressions of GS1;1, GS1;2 and GS2, which were tightly coupled with the expressions of PEPC1 and PEPC2 under WD stress.Conclusions: Our results suggest that the inhibited nitrate reduction associated with diminished electron transport rate, and the photorespiration-associated accumulation of hydrogen peroxide and NH3 were critical in the drought-induced rice growth inhibition. [ABSTRACT FROM AUTHOR]

An assessment of adaptability of saplings of four evergreen species (Picea abies Karst., Pinus mugo Turra, Pinus peuce Grisb. and Pinus heldreichii H. Christ.), native for Bulgarian treeline zone, was made on the basis of leaf gas exchange and survivability in artificially induced drought stress. The established low sensitivity of gas exchange to summer drought and the highest mortality of P. abies may be regarded as an evidence for a narrow zone of tolerance. P. peuce and P. heldreichii have low survivorship under drought conditions, regardless of the variable effect of soil moisture on the gas exchange parameters. The better survivability and significant reduction of gas exchange in response to soil water deficit of P. mugo probably will give him an advantage in future adaptation to climate change and in competition with other subalpine species. We conclude that the expected trends in climate change will most likely lead to a further narrowing of the ecological and physiological comfortable zone for two investigated endemic species. [ABSTRACT FROM AUTHOR]

Drought stress is one of the main environmental factors limiting plant growth and productivity of many crops. Elevated carbon dioxide concentration (eCO2) can ameliorate, mitigate, or compensate for the negative impact of drought on plant growth and enable plants to remain turgid and functional for a longer period. In order to investigate the combined effects of eCO2 and drought stress on photosynthetic performance and leaf structures, we analyzed photosynthetic characteristics and structure and ultrastructure of cucumber leaves. The decline in net photosynthetic rate under moderate drought stress occurred due to stomatal limitation alone, while under severe drought stress, it was the result of stomatal and nonstomatal limitations. Conversely, eCO2 improved photosynthetic performance under moderate drought stress, increased the lengths of the palisade cells and the number of chloroplasts per palisade cell under severe drought stress, and significantly increased the grana thickness under moderate drought stress. Additionally, eCO2 significantly decreased stomatal density, stomatal widths and stomatal aperture on the abaxial surface of leaves under moderate drought stress. In conclusion, eCO2 can alleviate the negative effects of drought stress by improving the drought resistance of cucumber seedlings through stomatal modifications and leaf structure. [ABSTRACT FROM AUTHOR]

Drought stress is a major global issue limiting agricultural productivity. Plants respond to drought stress through a series of physiological, cellular, and molecular changes for survival. The regulation of water transport and photosynthesis play crucial roles in improving plants’ drought tolerance. Nitrogen (N, ammonium and nitrate) is an essential macronutrient for plants, and it can affect many aspects of plant growth and metabolic pathways, including water relations and photosynthesis. This review focuses on how drought stress affects water transport and photosynthesis, including the regulation of hydraulic conductance, aquaporin expression, and photosynthesis. It also discusses the cross talk between N, water transport, and drought stress in higher plants. [ABSTRACT FROM AUTHOR]

Drought stress is a prominent and persisting constraint for sustaining global rice (Oryza sativa L.) production. Priming with mild drought can be effective in reducing the impact of severe terminal drought stress affecting seed set and grainfilling in rice. The cultivars N22(drought tolerant),NSIC Rc222 and IR64 (high yielding, drought sensitive) were tested for short-term mild drought priming before flowering and subsequently exposed to severe drought stress either at the highly sensitive flowering or at the early grain filling stage under greenhouse conditions. Drought stress increased oxidative damage and reduced photosynthesis and sink enzymatic activity, ultimately reducing seed set (20-46%) and grain yield (22-68%) across cultivars. However, priming with mild drought significantly reduced oxidative damage, and increased photosynthesis, stomatal conductance and enzymatic activity, contributing to improved sink strength, thereby significantly reducing seed set (7-18%) and grain yield (12-59%) losses. The higher activity of key enzymes associated with sink strength such as cell wall invertase and sucrose synthase in primed plants probably reduced drought-induced losses at the grain filling stage. The findings support mild drought priming before flowering as a promising strategy for reducing yield penalty by providing partial protection against subsequent severe terminal drought stress. However, application of mild drought priming at the field level would need further investigation. [ABSTRACT FROM AUTHOR]

A two-year study was carried out with split-plot factorial arrangement based on randomized complete block design in three replications in Khorramabad, Iran, during 2012-2014. The studied factors in the main-plots included end season drought stress at three levels (normal irrigation, mild stress and severe stress with irrigation based on 40%, 60% and 80% moisture depletion of soil water available to plants) and mycorrhizal biofertilizer factors and methanol spraying at four levels (without mycorrhiza inoculation + distilled water spraying, control; mycorrhiza inoculation + distilled water spraying; without mycorrhiza inoculation + methanol spraying; and mycorrhiza inoculation + methanol spraying). Moreover, the three irrigated wheat cultivars Aflak, Dena and Alvand with factorial arrangement were in sub-plots. Results demonstrated that drought stress decreased stomatal conductance, leaf transpiration, photosynthesis rate and grain yield. Crop plants under mild stress conditions experienced lower carbon dioxide in sub-stomatal chamber, whereas, its accumulation in those plants that were under severe stress conditions increased significantly. The studied cultivars responded to drought stress differently. Yield reduction in Alvand was more severe than in Aflak and Dena under mild and severe drought stress conditions. The results suggested that mycorrhizal inoculation and methanol spraying play an important role in enhancing drought tolerance in susceptible wheat cultivars to drought stress. Moreover, they can be used in irrigated wheat farming to reduce damages caused by end season drought stress. [ABSTRACT FROM AUTHOR]

In general medicinal plants grown under water limiting conditions show much higher concentrations of secondary metabolites in comparison to control plants. In the present study, Withania somnifera plants were subjected to water stress and data related to drought tolerance phenomenon was collected and a putative mechanistic concept considering growth responses, physiological behaviour, and metabolite content and gene expression aspects is presented. Drought induced metabolic and physiological responses as well as drastic decrease in CO 2 uptake due to stomatal limitations. As a result, the consumption of reduction equivalents (NADPH 2+ ) for CO 2 assimilation via the calvin cycle declines significantly resulting in the generation of a large oxidative stress and an oversupply of antioxidant enzymes. Drought also results in the shifting of metabolic processes towards biosynthetic activities that consume reduction equivalents. Thus, biosynthesis of reduced compounds (isoprenoids, phenols and alkaloids) is enhanced. The dynamics of various metabolites have been discussed in the light of gene expression analysis of control and drought treated leaves. Gene encoding enzymes of pathways leading to glucose, fructose and fructan production, conversion of triose phosphates to hexoses and hexose phosphorylation were up-regulated in the drought stressed leaves. The down-regulated Calvin cycle genes were co-ordinately regulated with the down-regulation of chloroplast triosephosphate/phosphate translocator, cytoplasmic fructose-1,6-bisphosphate aldolase and fructose bisphosphatase. Expression of gene encoding Squalene Synthase (SQS) was highly upregulated under drought stress which is responsible for the diversion of carbon flux towards withanolides biosynthesis from isoprenoid pathway. [ABSTRACT FROM AUTHOR]

The carbon starvation hypothesis (CSH) is one of the current leading hypotheses regarding the mechanism of plant death, although it has not been sufficiently validated due to a lack of evidence. To help verify the role of carbon starvation in plant mortality, we measured the non-structural carbohydrate (NSC) concentration ([NSC]) in different organs (roots, stems, and leaves) of plants of Catlapa bungei clone 9-1 after the cessation of photosynthesis and death due to drought and in well-watered controls. Drought induced the loss of NSC reserves, which was observed in all organs at death, and carbon starvation appeared to begin after the cessation of photosynthesis. The [NSC] dynamics, occurrence time of carbon starvation, and survival time varied among the organs, and even within the same organs at different stem heights. Overall, our findings are compatible with the CSH in that carbon starvation occurs in roots, stems, and leaves and concurs with plant death during prolonged drought. [ABSTRACT FROM AUTHOR]

Biogenic isoprene emissions play a very important role in atmospheric chemistry. These emissions are strongly dependent on various environmental conditions, such as temperature, solar radiation, plant water stress, ambient ozone and CO 2 concentrations, and soil moisture. Current biogenic emission models (i.e., Model of Emissions of Gases and Aerosols from Nature, MEGAN) can simulate emission responses to some of the major driving variables, such as short-term variations in temperature and solar radiation, but the other factors are either missing or poorly represented. In this paper, we propose a new modelling approach that considers the physiological effects of drought stress on plant photosynthesis and isoprene emissions for use in the MEGAN3 biogenic emission model. We test the MEGAN3 approach by integrating the algorithm into the existing MEGAN2.1 biogenic emission model framework embedded into the global Community Land Model of the Community Earth System Model (CLM4.5/CESM1.2). Single-point simulations are compared against available field measurements at the Missouri Ozarks AmeriFlux (MOFLUX) field site. The modelling results show that the MEGAN3 approach of using of a photosynthesis parameter (V cmax ) and soil wetness factor (β t ) to determine the drought activity factor leads to better simulated isoprene emissions in non-drought and drought periods. The global simulation with the MEGAN3 approach predicts a 17% reduction in global annual isoprene emissions, in comparison to the value predicted using the default CLM4.5/MEGAN2.1 without any drought effect. This reduction leads to changes in surface ozone and oxidants in the areas where the reduction of isoprene emissions is observed. Based on the results presented in this study, we conclude that it is important to simulate the drought-induced response of biogenic isoprene emission accurately in the coupled Earth System model. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems are expected to experience more intense and longer drought and heat-waves in the future. How these environmental factors and their interaction influence photosynthetic activity and water use efficiency remains, however, an open question. Since the photosynthetic activity determines yield response, we investigated gas-exchange and chlorophyll fluorescence traits of flag leaves in four winter wheat cultivars, including two genotypes widely grown in Central Europe and two genotypes considered as drought tolerant. Pot-grown plants were cultivated under natural field conditions until anthesis (DC 61). Subsequently, the plants were exposed to a set of temperature regimes with daily maxima of 26–41 °C (temperature treatment) and maximum soil water holding capacity above 70% and below 30% (drought treatment) using laboratory growth chambers. Primary photochemical reactions after 7 and 14 days of acclimation, measured as maximum quantum yield of photosystem II photochemistry and total chlorophyll content, showed typical interactions of temperature and water availability resulting in an amplified response under combined influence of drought and temperatures above 35 °C. In contrast, drought and temperature treatment had only minor effects on content of epidermal flavonols. A dominant effect of drought over temperature on stomatal conductance ( G Smax ) was observed. Although substantial genotype-specific responses were found, reduced stomatal conductance resulted in significant decrease in light-saturated rates of CO 2 assimilation ( A max ) in all genotypes studied. The G Smax – A max relationship, however, revealed limitation of CO 2 uptake by other, non-stomatal processes at temperatures above 32 °C, particularly in the sensitive genotypes. Strong interaction of combined drought and temperature treatments was found on water use efficiency (WUE). Decline in WUE with increasing temperature was steeper in water-deficit than well-watered plants of all genotypes studied. Our results thus document a strong interactive effect of elevated temperature and drought on photosynthetic carbon uptake. Detected thresholds of sensitivity to combined drought and heat stress will contribute to improved modelling of wheat growth and production under expected future climate conditions. [ABSTRACT FROM AUTHOR]

We investigated the physiological and morphological responses in six agroforestry tree species Dipterocarpus tuberculatus, D. alatus, Eucalyptus camaldulensis, Hevea brasiliensis, Colocasia gigantea, C. esculenta under limited water availability. Withholding water resulted in reduced field capacity by 71%, 86%, and 48% in D. alatus, D. tuberculatus, and E. camaldulensis, respectively, resulting in wilting, leaf chlorosis, and leaf burn, respectively. Stomatal density varied among the plant species (1.4-6.2 stomata per 0.0625 mm2) and was unaffected by water regimes, whereas stomatal conductance (gs), transpiration rate (E), and water use efficiency were reduced when plants were subjected to water deficit conditions. Generally, intracellular CO2 of well-watered plants was not always maintained across increasing light intensity flux (PARi), although for E. camaldulensis this was not the case, as both wellwatered and water deficit groups showed a reduction with increasing PARi. Net photosynthetic rate was significantly increased in well-watered plants as compared to water stressed plants, depending on the degree of PARi. In addition, a positive relation between gs and E in each plant was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Amazon droughts have impacted regional ecosystem functioning as well as global carbon cycling. The severe dry‐season droughts in 2005 and 2010, driven by Atlantic sea surface temperature (SST) anomaly, have been widely investigated in terms of drought severity and impacts on ecosystems. Although the influence of Pacific SST anomaly on wet‐season precipitation has been well recognized, it remains uncertain to what extent the droughts driven by Pacific SST anomaly could affect forest greenness and photosynthesis in the Amazon. Here, we examined the monthly and annual dynamics of forest greenness and photosynthetic capacity when Amazon ecosystems experienced an extreme drought in 2015/2016 driven by a strong El Niño event. We found that the drought during August 2015–July 2016 was one of the two most severe meteorological droughts since 1901. Due to the enhanced solar radiation during this drought, overall forest greenness showed a small increase, and 21.6% of forests even greened up (greenness index anomaly ≥1 standard deviation). In contrast, solar‐induced chlorophyll fluorescence (SIF), an indicator of vegetation photosynthetic capacity, showed a significant decrease. Responses of forest greenness and photosynthesis decoupled during this drought, indicating that forest photosynthesis could still be suppressed regardless of the variation in canopy greenness. If future El Niño frequency increases as projected by earth system models, droughts would result in persistent reduction in Amazon forest productivity, substantial changes in tree composition, and considerable carbon emissions from Amazon. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that effective antioxidant and photoprotective mechanisms are able to avoid photodamage induced by prolonged water deficit (WD) followed by high light (HL). We employed cashew plants ( Anacardium occidentale L.), a semiarid adapted species, as a model plant. WD-plants exposed to HL did not show alterations in maximum quantum efficiency of photosystem II (Fv/Fm), cellular integrity, H 2 O 2 and thiobarbituric acid reactive species (TBARS) contents, evidencing that they did not suffered photoinhibition and oxidative stress. These responses were associated with increases in ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, glutathione (GSH) oxidation and ascorbate (ASC) synthesis. This effective oxidative protection occurred in parallel to strong decrease in photosystem II and I (PSII and PSI) activities, increase in heat dissipation (qE), which was related to enhancement in cyclic electron flux. These favorable photoprotective changes were associated with efficient water use in response to HL, all contributing to avoid excess energy in chloroplasts of drought-exposed leaves. These protective features were associated with a tight regulation in D1 protein accumulation during HL, contributing to avoid reactive oxygen species over-accumulation and a subsequent effective PSII recovery during darkness. Our results indicate that cashew plants are able to avoid photoinhibition, tolerating extreme conditions of drought combined with HL. The displayed mechanisms involve essentially integrated responses to balance energy input and output, avoiding oxidative stress. [ABSTRACT FROM AUTHOR]

Changes of endogenous polyamine (PA) levels could be a key adaptive response to drought in plants. White clover pretreated with or without dicyclohexylamine (DCHA), an inhibitor of PA biosynthesis, was subjected to drought stress induced by 18% polyethylene glycol 6000 for 8 days in controlled growth chambers. Results showed that drought stress significantly increased endogenous PA content, whereas DCHA significantly decreased PA accumulation under drought stress. The attenuate PA biosynthesis was unfavorable for plant growth and drought tolerance, as reflected by significantly lower relative water content, relative growth rate, instantaneous water use efficiency, and cell membrane stability in leaves in response to drought. On the basis of proteomic analysis, the inhibition of PA synthesis decreased the accumulation of many key differentially expressed proteins including (1) ribosomal structure and biogenesis: elongation factor, ribosomal protein S10E, and 30S ribosomal protein; (2) amino acid transport and metabolism: cysteine synthase, delta-1-pyrroline-5-carboxylate synthetase, and glutamate decarboxylase; (3) carbohydrate metabolism and energy production: photosystem apoprotein, sucrose-phosphate synthase, phosphogluconate dehydrogenase, sucrose-phosphatase, NADH oxidoreductase, and ATP synthase; (4) antioxidant metabolism: catalase, peroxidase I, ascorbate peroxidase, and glutathione S-transferase; and (5) other biological processes: heat shock protein 70, heat shock protein 90, and calcium-dependent protein kinase associated with the decreased drought tolerance in white clover. These findings indicate that PAs play a critical role in the regulation of growth, ribosome, amino acid and energy metabolism, and antioxidant reactions in white clover under drought stress. Drought-induced increases in endogenous PAs could be one of key adaptive responses against drought stress in white clover. [ABSTRACT FROM AUTHOR]

Drought‐induced reduction of leaf gas exchange entails a complex regulation of the plant leaf metabolism. We used a combined molecular and physiological approach to understand leaf photosynthetic and respiratory responses of 2‐year‐old Quercus ilex seedlings to drought. Mild drought stress resulted in glucose accumulation while net photosynthetic CO2 uptake (Pn) remained unchanged, suggesting a role of glucose in stress signaling and/or osmoregulation. Simple sugars and sugar alcohols increased throughout moderate‐to‐very severe drought stress conditions, in parallel to a progressive decline in Pn and the quantum efficiency of photosystem II; by contrast, minor changes occurred in respiration rates until drought stress was very severe. At very severe drought stress, 2‐oxoglutarate dehydrogenase complex gene expression significantly decreased, and the abundance of most amino acids dramatically increased, especially that of proline and γ‐aminobutyric acid (GABA) suggesting enhanced protection against oxidative damage and a reorganization of the tricarboxylic cycle acid cycle via the GABA shunt. Altogether, our results point to Q. ilex drought tolerance being linked to signaling and osmoregulation by hexoses during early stages of drought stress, and enhanced protection against oxidative damage by polyols and amino acids under severe drought stress. [ABSTRACT FROM AUTHOR]

Guzmania monostachia (Bromeliaceae) is a tropical epiphyte capable of up-regulating crassulacean acid metabolism (CAM) in its photosynthetic tissues in response to changing nutrient and water availability. Previous studies have shown that under drought there is a gradient of increasing CAM expression from the basal (youngest) to the apical (oldest) portion of the leaves, and additionally that nitrogen deficiency can further increase CAM intensity in the leaf apex of this bromeliad. The present study investigated the inter-relationships between nitrogen source (nitrate and/or ammonium) and water deficit in regulating CAM expression in G. monostachia leaves. The highest CAM activity was observed under ammonium nutrition in combination with water deficit. This was associated with enhanced activity of the key enzyme phosphoenolpyruvate carboxylase, elevated rates of ATP- and PPi-dependent proton transport at the vacuolar membrane in the presence of malate, and increased transcript levels of the vacuolar malate channel- encoding gene, ALMT. Water deficit was consistently associated with higher levels of total soluble sugars, which were maximal under ammonium nutrition, as were the activities of several antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase). Thus, ammonium nutrition, whilst associated with the highest degree of CAM induction in G. monostachia, also mitigates the effects of water deficit by osmotic adjustment and can limit oxidative damage in the leaves of this bromeliad under conditions that may be typical of its epiphytic habitat. [ABSTRACT FROM AUTHOR]

The physiological performance of some sunflower genotypes (S.28111, SF0049, Hysun-33, Hysun-39) under salt, drought stress separately and in combination was examined. Salt, drought and a combination of these stresses were applied to plants by gradual increments. The plants were exposed to stress for two weeks. Relative water content, osmotic potential, stomatal conductance, performance index, dark adapted quantum yield and chlorophyll contents were reduced upon salinity and drought stresses. However, when plants were subjected to a combination of these stresses, a greater reduction in all tested attributes was observed. Proline and carotenoid contents in drought stress were elevated compared to salt stress. Superoxide dismutase (SOD) and catalase (CAT) showed the highest activity in individual salt and drought stress with less accumulation of H2O2. Combined stress reduced the activity of antioxidant enzymes which ultimately decreased the physiological performance of sunflower plants. However, among the tested genotypes, S.28111 and SF0049 were found to be more tolerant to drought, salt and combined stress than both Hysun genotypes. The physiological performance of genotypes against salinity and drought individually and in combination is discussed in detail. [ABSTRACT FROM AUTHOR]

Ascorbate-glutathione (ASA-GSH) cycle is a major pathway of H2O2 scavenging and an effective mechanism of detoxification in plants. The differences in photosynthesis, chlorophyll content (Chl), relative water content (RWC), antioxidants and antioxidative enzyme activities involved in ASA-GSH metabolism were measured between the flag leaves and spike bracts (glumes and lemmas) during grain filling under drought stress. The expression of APX1, GRC1, DHAR, MDHAR, GPX1, and GS3 in ASA-GSH cycle was also measured. Compared with the flag leaves, the spike bracts exhibited stable net photosynthetic rate (PN) and chlorophyll content (Chl), a lower accumulation of reactive oxygen species (ROS), and more enhanced percentages of antioxidant enzyme activities and key enzymes gene transcription levels involved in ASA-GSH metabolism during the grain-filling stage under drought conditions. This could be the reasonable explanation for the more stable photosynthetic capacity in spikes, and the glumes and lemmas senesced later than the flag leaves at the late grain-filling stage. Also, the function of ASA-GSH cycle could not be ignored in alleviating oxidative damage by scavenging more excess ROS in spikes under drought stress. [ABSTRACT FROM AUTHOR]

Abiotic stresses such as drought, heat or salinity are major causes of yield loss worldwide. Recent studies have revealed that the acclimation of plants to a combination of different environmental stresses is unique and therefore cannot be directly deduced from studying the response of plants to each of the different stresses applied individually. The efficient detoxification of reactive oxygen species (ROS) is thought to play a key role in enhancing the tolerance of plants to abiotic stresses. Here, we report on the role of melatonin in the protection of the photosynthetic apparatus through the increase in ROS detoxification in tomato plants grown under the combination of salinity and heat, two of the most common abiotic stresses known to act jointly. Plants treated with exogenous melatonin showed a different modulation in the expression on some antioxidant-related genes and their related enzymes. More specifically, ascorbate peroxidase, glutathione reductase, glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase (APX, GR, GPX and Ph-GPX, resepctively) showed an antagonistic regulation as compared to plants that did not receive melatonin. This translated into a better antioxidant capacity and to a lesser ROS accumulation under stress combination. The performance of the photosynthesis parameters and the photosystems was also increased in plants treated with exogenous melatonin under the combination of salinity and heat. In accordance with these findings, tomato plants treated with melatonin were found to grow better under stress combination that the non-treated ones. Our study highlights the important role that exogenous melatonin plays in the acclimation of plants to a combination of two different abiotic stresses, and how this compound can specifically regulate oxidative stress-related genes and enzymes to increase plant tolerance. [ABSTRACT FROM AUTHOR]

Photoassimilate distribution inside leaves is less studied than photosynthesis, and yet the topic is important as it gives insights into the vital roles played by leaves in plant survival. We combined greenhouse measurements of light response curves with 11C-labelling using leaves of 3-year-old potted Maesopsis eminii Engl. trees to improve our understanding of its leaf carbon physiology. This fast-growing pioneer tree species showed low photosynthetic rates for a common tropical pioneer during well-watered reference conditions (5.0 ± 0.7 µmol m-2 s-1), which further decreased in response to drought. 11C-autoradiography indicated active phloem loading and/or rapid phloem transport rates. Active loading is uncommon in tree species, but might be related to deciduousness traits and continuous investment in growth, like in herbaceous active loaders. Active loading involves higher carbon allocation to growth, which might explain why low photosynthetic rates were observed in this fast-growing species. These findings suggest that examining photoassimilate distribution and transport may be critical for understanding the role tree physiology plays in terrestrial carbon cycling. [ABSTRACT FROM AUTHOR]