Alterations in carbon and nitrogen metabolism induced by water deficit in the stems and leaves of Lupinus albus L

Effect of deficit irrigation combined with Bacillus simplex on water use efficiency and growth parameters of maize during vegetative stage

The production of crops depending on many factors including water, nutrient, soil types, climate and crops types, water stress and drought is in one of the important factors affecting crop productivity. The experiment was conducted in pots to evaluate the effect of biofertilizers (Bacillus simplex) with deficit irrigations on the early development and growth of maize crop under greenhouse condition. Pre sowing seed was inoculated with strain of bacteria (B+/B-) and different irrigation levels (no stress: 100% (I1) and deficit irrigation: 75 (I2), 50 (I3), 25 (I4) % of required water amount to reach pot capacity) was performed. Data was collected on different morphological characteristics and root characteristic of maize crop. Highest plant height (125 cm), stem diameter (18.02 mm), leaf area (350 cm- 2), plant weight (180.42 g in fresh, 73.58 g in dry), root length (92.83 cm) root ((91.70 g in fresh, (28.66 g in dry) weight were recorded in pots applied with 100% irrigation followed by 75%. Bacillus treated plants showed significant increase in leaf area (214.20 cm- 2), plant fresh weight (91.65 g) and dry weight (42.05 g), root length (79.20 cm), root fresh (53.52 g) and dry weight (16.70 g) compared with control (without bacteria). Likewise highest relative water content of leaf was observed with I3 followed by I2 and I1 respectively. Highest water use efficiency was recorded as 0.67 g pot- 1 mm- 1 in I1 with B + treatment. Likewise, Bacillus inoculated pots resulted in increased water use efficiency (0.44 g pot- 1 mm- 1) compared with no application (0.36 g pot- 1 mm- 1). It can be endorsed from the outcome that Bacillus inoculation increased plant biomass, root biomass of maize and water use efficiency during early growth stage of maize despite of water stress and can be used under limited water condition for crop combating during moderate to lower stress conditions.

Secretome analysis revealed that cell wall remodeling and starch catabolism underlie the early stages of somatic embryogenesis in Pinus nigra

Somatic embryogenesis is an efficient mean for rapid micropropagation and preservation of the germplasm of valuable coniferous trees. Little is known about how the composition of secretome tracks down the level of embryogenic capacity. Unlike embryogenic tissue on solid medium, suspension cell cultures enable the study of extracellular proteins secreted into a liquid cultivation medium, avoiding contamination from destructured cells. Here, we present proteomic data of the secretome of Pinus nigra cell lines with contrasting embryogenic capacity, accounting for variability between genotypes. Our results showed that cell wall-related and carbohydrate-acting proteins were the most differentially accumulated. Peroxidases, extensin, α-amylase, plant basic secretory family protein (BSP), and basic secretory protease (S) were more abundant in the medium from the lines with high embryogenic capacity. In contrast, the medium from the low embryogenic capacity cell lines contained a higher amount of polygalacturonases, hothead protein, and expansin, which are generally associated with cell wall loosening or softening. These results corroborated the microscopic findings in cell lines with low embryogenic capacity-long suspensor cells without proper assembly. Furthermore, proteomic data were subsequently validated by peroxidase and α-amylase activity assays, and hence, we conclude that both tested enzyme activities can be considered potential markers of high embryogenic capacity.

Integration of transcriptomic and metabolomic analysis unveils the response mechanism of sugar metabolism in Cyclocarya paliurus seedlings subjected to PEG-induced drought stress

Cyclocarya paliurus (Batal.) Iljinskaja is a multiple function tree species used for functional food and valued timber production. Carbohydrates, especially water-soluble carbohydrates, play an important role in osmotic protection, signal transduction and carbon storage. Under the circumstance of global climate change the abiotic stress would restrict the development of C. paliurus plantation, whereas there is few knowledge on the regulatory mechanisms of sugar metabolism under drought stress in C. paliurus. To investigate the drought response of C. paliurus at molecular level, we conducted an integrated analysis of transcriptomic and metabolomic of C. paliurus at three PEG-induced drought stress levels (0%: control; 15%: moderate drought; 25%: severe drought) in short term. Both moderate and severe drought treatments activated the chemical defense with lowering relative water content, and enhancing the contents of soluble protein, proline and malondialdehyde in the leaves. Meanwhile, alterations in the expression of differentially expressed genes and carbohydrate metabolism profiles were observed among the treatments. Weighted gene co-expression network analysis (WGCNA) showed 3 key modules, 8 structural genes (such as genes encoding beta-fructofuranosidase (INV), sucrose synthase (SUS), raffinose synthase (RS)) and 14 regulatory transcription factors were closely linked to sugar metabolism. Our results provided the foundation to understand the response mechanism of sugar metabolism in C. paliurus under drought stress, and would drive progress in breeding of drought-tolerant varieties and plantation development of the species.

Age-related differences in physiological and metabolic responses of Pleione aurita (Orchidaceae) pseudobulbs to drought stress and recovery

The pseudobulb is a storage organ for water and nutrients that plays a crucial role in the growth and survival of epiphytic orchids. However, the role of water and metabolites in pseudobulb during adaptation to environmental stress are rarely detected through control experiments. In the present study, water-related physiological traits and metabolite changes in the pseudobulbs at the flowering stage and full leaf expansion stage for Pleione aurita were investigated after drought stress and recovery treatments. We found that the composition of non-structural carbohydrates (starch vs. soluble sugar) varied over the lifetime of pseudobulbs, and older pseudobulbs stored more water, whereas younger pseudobulbs stored more dry matter. When plants were subjected to drought stress and subsequent recovery, multiple metabolites in the pseudobulbs including non-structural carbohydrates, flavonoids, phenolic acids, as well as amino acids and their derivatives responded positively to these water level fluctuations. For those metabolites that differently accumulated in both stress and recovery processes, old pseudobulbs contained a higher number of these key metabolites than did the connected younger pseudobulbs. In addition, young and old pseudobulbs use different metabolic pathways to both respond and recover to drought. These results indicate that orchid pseudobulbs cope with water level fluctuations by mobilizing metabolite reserves and that pseudobulbs of different ages exhibit different physiological and metabolic responses to drought stress. These findings broadens our understanding of the role pseudobulbs play in the survival of orchids growing in epiphytic habitats.

Functional Dissection of the Physiological Traits Promoting Durum Wheat (Triticum durum Desf.) Tolerance to Drought Stress

In Tunisia's arid and semi-arid lands, drought stress remains the most critical factor limiting agricultural production due to low and irregular precipitation. The situation is even more difficult because of the scarcity of underground water for irrigation and the climate change that has intensified and expanded the aridity. One of the most efficient and sustainable approaches to mitigating drought stress is exploring genotypic variability to screen tolerant genotypes and identify useful tolerance traits. To this end, six Tunisian wheat genotypes (Triticum durum Desf.) were cultivated in the field, under a greenhouse and natural light, to be studied for their differential tolerance to drought stress. Many morpho-physiological and biochemical traits were analyzed, and interrelationships were established. Depending on the genotypes, drought stress significantly decreased plant growth, chlorophyll biosynthesis, and photosynthesis; stimulated osmolyte accumulation and disturbed water relations. The most tolerant genotypes (salim and karim) accumulated more potassium (K) and proline in their shoots, allowing them to maintain better tissue hydration and physiological functioning. The osmotic adjustment (OA), in which potassium and proline play a key role, determines wheat tolerance to drought stress. The calculated drought index (DI), drought susceptible index (DSI), drought tolerance index (DTI), K use efficiency (KUE), and water use efficiency (WUE) discriminated the studied genotypes and confirmed the relative tolerance of salim and karim.

White Lupin Drought Tolerance: Genetic Variation, Trait Genetic Architecture, and Genome-Enabled Prediction

White lupin is a high-protein crop requiring drought tolerance improvement. This study focused on a genetically-broad population of 138 lines to investigate the phenotypic variation and genotype × environment interaction (GEI) for grain yield and other traits across drought-prone and moisture-favourable managed environments, the trait genetic architecture and relevant genomic regions by a GWAS using 9828 mapped SNP markers, and the predictive ability of genomic selection (GS) models. Water treatments across two late cropping months implied max. available soil water content of 60-80% for favourable conditions and from wilting point to 15% for severe drought. Line yield responses across environments featured a genetic correlation of 0.84. Relatively better line yield under drought was associated with an increased harvest index. Two significant QTLs emerged for yield in each condition that differed across conditions. Line yield under stress displayed an inverse linear relationship with the onset of flowering, confirmed genomically by a common major QTL. An adjusted grain yield computed as deviation from phenology-predicted yield acted as an indicator of intrinsic drought tolerance. On the whole, the yield in both conditions and the adjusted yield were polygenic, heritable, and exploitable by GS with a high predictive ability (0.62-0.78). Our results can support selection for climatically different drought-prone regions.

Proteomic Investigation of Molecular Mechanisms in Response to PEG-Induced Drought Stress in Soybean Roots

Roots are generally the critical drought sensors, but little is known about their molecular response to drought stress. We used the drought-tolerant soybean variety ‘Jiyu 47’ to investigate the differentially expressed proteins (DEPs) in soybean roots during the seedling stage based on the tandem mass tag (TMT) proteomics analysis. Various expression patterns were observed in a total of six physiological parameters. A total of 468 DEPs (144 up-regulated and 324 down-regulated) among a total of 8687 proteins were identified in response to drought stress in 24 h. The expression of DEPs was further validated based on quantitative real-time PCR of a total of five genes (i.e., GmGSH, GmGST1, GmGST2 k GmCAT, and Gm6PGD) involved in the glutathione biosynthesis. Results of enrichment analyses revealed a coordinated expression pattern of proteins involved in various cellular metabolisms responding to drought stress in soybean roots. Our results showed that drought stress caused significant alterations in the expression of proteins involved in several metabolic pathways in soybean roots, including carbohydrate metabolism, metabolism of the osmotic regulation substances, and antioxidant defense system (i.e., the glutathione metabolism). Increased production of reduced glutathione (GSH) enhanced the prevention of the damage caused by reactive oxygen species and the tolerance of the abiotic stress. The glutathione metabolism played a key role in modifying the antioxidant defense system in response to drought stress in soybean roots. Our proteomic study suggested that the soybean plants responded to drought stress by coordinating their protein expression during the vegetative stage, providing novel insights into the molecular mechanisms regulating the response to abiotic stress in plants.

Alteration of physiological and biochemical properties in leaves and fruits of pomegranate in response to gamma irradiation

Pomegranate breeding to improve the marketability requires the production of large and high quality fruits. Gamma radiation on pomegranate can be used to generate genetic diversity that allows the breeder to screen the mutants for superior quality and quantity. For this purpose, dormant buds on 1-year-old shoots of pomegranate cultivar "Malase Saveh" were subjected to 36 Gy (Gy) of gamma irradiation from a cobalt (⁶⁰CO) source. Shoot cuttings were taken from the mutated shoots and generate M₁V₂. The number of 11 mutants were selected from M₁V₂ plants based on their winter survival and disease resistance. After a period of 3–4 years, leaf and fruit samples were harvested from the M₁V₅. Results showed that physiological and biochemical parameters of leaves were altered unevenly, some clones showed no alterations from the control, while others revealed considerable differences. Irradiation altered various aspects related to fruit, such as the number and weight of ripe and unripe fruits, number of cracked, sunburn, worm-eaten fruits, and fruit size. In general, mutant clones 5, 8, and 10 had higher fruit sizes and weight of ripe fruits and less number and weight of unripe fruits. The stability of the detected mutants will be evaluated and new commercial field trials using selected materials will be established.

Hydrogen sulfide (H2S) and potassium (K+) synergistically induce drought stress tolerance through regulation of H+-ATPase activity, sugar metabolism, and antioxidative defense in tomato seedlings

Exogenous potassium (K⁺) and endogenous hydrogen sulfide (H₂S) synergistically alleviate drought stress through regulating H⁺-ATPase activity, sugar metabolism and redox homoeostasis in tomato seedlings. Present work evaluates the role of K⁺ in the regulation of endogenous H₂S signaling in modulating the tolerance of tomato (Solanum lycopersicum L. Mill.) seedlings to drought stress. The findings reveal that exposure of seedlings to 15% (w/v) polyethylene glycol 8000 (PEG) led to a substantial decrease in leaf K⁺ content which was associated with reduced H⁺-ATPase activity. Treatment with sodium orthovanadate (SOV, PM H⁺-ATPase inhibitor) and tetraethylammonium chloride (TEA, K⁺ channel blocker) suggests that exogenous K⁺ stimulated H⁺-ATPase activity that further regulated endogenous K⁺ content in tomato seedlings subjected to drought stress. Moreover, reduction in H⁺-ATPase activity by hypotaurine (HT; H₂S scavenger) substantiates the role of endogenous H₂S in the regulation of H⁺-ATPase activity. Elevation in endogenous K⁺ content enhanced the biosynthesis of H₂S through enhancing the synthesis of cysteine, the H₂S precursor. Synergistic action of H₂S and K⁺ effectively neutralized drought stress by regulating sugar metabolism and redox homoeostasis that resulted in osmotic adjustment, as witnessed by reduced water loss, and improved hydration level of the stressed seedlings. The integrative role of endogenous H₂S in K⁺ homeostasis was validated using HT and TEA which weakened the protection against drought stress induced impairments. In conclusion, exogenous K⁺ and endogenous H₂S regulate H⁺-ATPase activity which plays a decisive role in the maintenance of endogenous K⁺ homeostasis. Thus, present work reveals that K⁺ and H₂S crosstalk is essential for modulation of drought stress tolerance in tomato seedlings.

Transcriptome Analysis of Tolerant and Susceptible Maize Genotypes Reveals Novel Insights about the Molecular Mechanisms Underlying Drought Responses in Leaves

Maize (Zea mays L.) is the most essential food crop in the world. However, maize is highly susceptible to drought stress, especially at the seedling stage, and the molecular mechanisms underlying drought tolerance remain elusive. In this study, we conducted comparative transcriptome and physiological analyses of drought-tolerant (CML69) and susceptible (LX9801) inbred lines subjected to drought treatment at the seedling stage for three and five days. The tolerant line had significantly higher relative water content in the leaves, as well as lower electrolyte leakage and malondialdehyde levels, than the susceptible line. Using an RNA-seq-based approach, we identified 10,084 differentially expressed genes (DEGs) with 6906 and 3178 DEGs been annotated and unannotated, respectively. Two critical sets of drought-responsive DEGs, including 4687 genotype-specific and 2219 common drought-responsive genes, were mined out of the annotated DEGs. The tolerant-line DEGs were predominantly associated with the cytoskeleton, cell wall modification, glycolysis/gluconeogenesis, transport, osmotic regulation, drought avoidance, ROS scavengers, defense, and transcriptional factors. For the susceptible line, the DEGs were highly enriched in the photosynthesis, histone, and carbon fixation pathways. The unannotated DEGs were implicated in lncRNAs, including 428 previously reported and 22% putative TE-lncRNAs. There was consensus on both the physiological response and RNA-seq outcomes. Collectively, our findings will provide a comprehensive basis of the molecular networks mediating drought stress tolerance of maize at the seedling stage.

Metabolite profiling of semi-leafless pea (Pisum sativum L.) under progressive soil drought and subsequent re-watering

Four semi-leafless pea (Pisum sativum L.) cultivars at the vegetative stage of growth were exposed to progressive soil drought, which lasted for 18 days until the plants began to wilt, after which a 7-day period of the recovery from stress followed, when plant watering was resumed. The soil drought negatively affected plant growth, slowing down the rate of shoot elongation, decreasing the accumulation of fresh and dry weight, inhibiting the development of new leaves, and delaying the flowering of plants. Changes in the levels of 41 polar metabolites (identified by GC-MS) were established by the GC-FID method in the shoot tip, stem, stipules and tendrils, separately. Drought caused re-arrangement in the metabolism in all parts of the pea shoot, leading to a significant increase in the content of total polar metabolites. Although changes in most metabolites in the same parts of shoot were not identical among the pea cultivars studied, some metabolites were uniformly accumulated until 18th day of drought and decreased after recovery. They were i) proline and malate in all, while myo-inositol in most parts of shoot (of all the pea cultivars), ii) sucrose and glycine in the shoot tip, iii) homoserine in the stem and iv) GABA in stipules. These findings signify that the pea adjustment to progressive soil drought includes both accumulation of osmolytes and osmoprotectants and translocation of some of them (proline, sucrose, myo-inositol) to the shoot tip, thereby protecting the youngest tissues from damage caused by water deficit.

Combined proteomics, metabolomics and physiological analyses of rice growth and grain yield with heavy nitrogen application before and after drought

BACKGROUND

Nitrogen application can effectively mitigate the damage to crop growth and yield caused by drought. However, the efficiency of heavy nitrogen application before drought (NBD) and heavy nitrogen application after drought (NAD) to regulate rice response to drought stress remains controversial. In this study, we profiled physiology, proteomics and metabolomics in rice variety Wufengyou 286 of two nitrogen management modes (NBD and NAD) to investigate their yield formation and the mechanism of nitrogen regulation for drought resistance.

RESULTS

Results revealed that the yield of NBD and NAD decreased significantly when it was subjected to drought stress at the stage of young panicle differentiation, while the yield of NBD was 33.85 and 36.33% higher than that of NAD in 2017 and 2018, reaching significant levels. Under drought conditions, NBD increased chlorophyll content and net photosynthetic rate in leaves, significantly improved the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase and catalase, and decreased malondialdehyde (MDA) content compared with NAD. NBD promoted nitrogen assimilation in leaves, which was characterized by increased activities of nitrate reductase (NR) and glutamine synthetase (GS). In addition, NBD significantly increased the contents of osmotic regulatory substances such as soluble sugar, soluble protein and free proline. Gene ontology and KEGG enrichment analysis of 234 differentially expressed proteins and 518 differential metabolites showed that different nitrogen management induced strong changes in photosynthesis pathway, energy metabolism pathway, nitrogen metabolism and oxidation-reduction pathways.

CONCLUSION

Different nitrogen management methods have significant differences in drought resistance of rice. These results suggest that heavy nitrogen application before drought may be an important pathway to improve the yield and stress resistance of rice, and provide a new ecological perspective on nitrogen regulation in rice.

Effect of drought stress on sugar metabolism in leaves and roots of soybean seedlings

Sucrose is the main photosynthetic product in plants, and acts as a major energy substrate and signaling regulator of plant growth. Furthermore, sucrose is involved in the responses to various abiotic stresses. However, the role of sucrose in soybean (Glycine max L.) growth and development under drought stress remains largely unknown. In this study, the two soybean cultivars, Shennong8 (CV.SN8) and Shennong12 (CV.SN12), were grown in pot culture and subjected to three water treatments for 15 days: soil moisture contents of 75 ± 5% (CK), 45 ± 5% (MD), and 30 ± 5% (SD) of field capacity. Under drought stress, the reduction in shoot biomass was more pronounced than the reduction of biomass in the root of both soybean cultivars, resulting in higher root/shoot (R/S) ratio. Drought stress increased the contents of soluble sugar and sucrose in the leaves, but decreased starch content; in the roots, all of these parameters were increased. This may be related to the enhanced carbohydrate metabolism activity under drought stress, including notable changes in the activities of sugar metabolism enzymes and expression levels of GmSPS, GmSuSy, GmC-INV, GmA-INV, GmAMY3, and GmBAM1. Furthermore, the expression levels of sucrose transporter genes (GmSUC2, GmSWEET6, and GmSWEET15) in leaves and roots of soybean seedlings were up-regulated under drought stress. In conclusion, our results highlight that the increase in R/S ratio caused by the changes of sugar allocation, metabolism, and transport under drought stress contributes towards drought resistance of soybean.

Variability of leaf photosynthetic characteristics in rice and its relationship with resistance to water stress under different nitrogen nutrition regimes

The negative effects of water stress on rice can be alleviated by NH₄ ⁺ nutrition. However, the effects of mixed nitrogen (N) nutrition (NO₃ ^-  + NH₄ ⁺ ) on resistance to water stress are still not well known. To investigate the response of rice growth to water stress and its relationship with photosynthetic characteristics, a hydroponic experiment supplying different N forms was conducted. Compared with NO₃ ^- nutrition, mixed-N and NH₄ ⁺ nutrition greatly alleviated the reduction of leaf area, chlorophyll content, and photosynthesis under water stress, whilst subsequently maintaining higher biomass. In contrast, water stress inhibited the root-shoot ratios in NH₄ ⁺ - and mixed-N-supplied plants, indicating reduced root growth and higher photosynthate availability to shoots. The following key observations were made: (1) a similar stomatal limitation and low proportion of activated Rubisco were observed among the three different N nutrition regimes; (2) increased mesophyll conductance in NH₄ ⁺ - and mixed-N-supplied plants simultaneously stimulated leaf photosynthesis and improved the water use efficiency and (3), the maximum carboxylation rate and actual photochemical efficiency of photosystem II in NH₄ ⁺ - and mixed-N-supplied plants were significantly higher than that in NO₃ ^- -supplied plants, thus resulting in higher photochemical efficiency under water stress. In conclusion, mixed-N and NH₄ ⁺ nutrition may be used to develop strategies for improved water stress resistance and stimulated biomass production under conditions of osmotic stress and possibly drought.

Comprehensive metabolomic, proteomic and physiological analyses of grain yield reduction in rice under abrupt drought-flood alternation stress

Abrupt drought-flood alternation (T1) is a meteorological disaster that frequently occurs during summer in southern China and the Yangtze river basin, often causing a significant loss of rice production. In this study, the response mechanism of yield decline under abrupt drought-flood alternation stress at the panicle differentiation stage was analyzed by looking at the metabolome, proteome as well as yield and physiological and biochemical indexes. The results showed that drought and flood stress caused a decrease in the yield of rice at the panicle differentiation stage, and abrupt drought-flood alternation stress created a synergistic effect for the reduction of yield. The main reason for the decrease of yield per plant under abrupt drought-flood alternation was the decrease of seed setting rate. Compared with CK0 (no drought and no flood), the net photosynthetic rate and soluble sugar content of T1 decreased significantly and its hydrogen peroxidase, superoxide dismutase, peroxidase activity increased significantly. The identified differential metabolites and differentially expressed proteins indicated that photosynthesis metabolism, energy metabolism pathway and reactive oxygen species response have changed strongly under abrupt drought-flood alteration stress, which are factors that leads to the rice grain yield reduction.

Photosynthetic Responses to High Temperature and Strong Light Suggest Potential Post-flowering Drought Tolerance of Sorghum Japanese Landrace Takakibi

Sorghum [Sorghum bicolor (L.) Moench] is a C4 crop known to be adaptable to harsh environments such as those under high temperature and water deficit. In this study, we focused on a Japanese sorghum landrace Takakibi (NOG) and employed chlorophyll fluorescence measurements to assess its response to environmental stress. Comparison of photosynthetic rate evaluated using two parameters (effective quantum yield and electron transfer rate) indicated that NOG showed less activity than BTx623 in the pre-flowering stage, which was consistent with the higher susceptibility of NOG seedlings to drought than BTx623. The observed differences in photosynthetic activity between the two cultivars were detectable without drought conditions on days with high temperature and strong light. Interestingly, the photosynthetic activity of NOG leaves in stress conditions increased soon after heading, and the trend was similar to that in BTx642, a well-characterized post-flowering drought-tolerant cultivar. In contrast, BTx623 showed a gradual decline in photosynthetic rate. Thus, we inferred that Japanese Takakibi has the potential to show pre-flowering drought susceptibility and post-flowering drought tolerance, through which it adapts to local climates with high temperature and strong light at harvest.

Response of sugar metabolism in apple leaves subjected to short-term drought stress

For a comprehensive understanding of gene expression, enzyme activity and sugar concentrations in response to short-term water deficit in apple (Greensleeves), sugar-modulated gene expression and enzyme activities were analyzed. Water stress resulted in the accumulation of sorbitol, glucose, fructose, galactose and starch, accompanied by a significant reduction in photosynthesis and sucrose concentration. In response to short-term water deficits, the activities of aldose-6-phosphate reductase (A6PR; EC 1.1.1.200), sorbitol dehydrogenase (SDH; EC 1.1.1.14), neutral invertase (NINV; EC 3.2.1.26), sucrose synthase (SUSY; EC 2.4.1.13), and fructokinase (FK; EC 2.7.1.4) were higher, whereas cell wall invertase (CWINV; EC 3.2.1.26) and hexokinase (HK; EC 2.7.1.1) activities were lower. In addition, sucrose phosphate synthase (SPS; EC 2.4.1.14) activity increased during the initial stages of dehydration and then decreased as the drought strengthened. Transcript levels of MdA6PR, MdSDH1/2, MdNINV1/2, MdSUSY3, MdFK1/2/4, MdSOT1/2, MdSUC1-3, MdTMT2/3, MdvGT1, MdpGlcT1-4 were upregulated, whereas transcript levels of MdCWINV1/2, MdHK1/2/3/5, and MdTMT1 were downregulated after 6 days of water stress. These findings suggest that the sorbitol metabolism pathway is induced and high levels of hexose derived from photosynthetic products are transported into vacuoles for adjustment to the water deficit. Our results provide insights into the relationships between sugar levels and sugar-modulated gene and enzyme activity in response to the imposition of short-term water stress.

Exogenous application of melatonin mitigates the adverse effects of drought stress on morpho-physiological traits and secondary metabolites in Moldavian balm (Dracocephalum moldavica)

Melatonin has emerged as an important signaling molecule that regulates plant responses to environmental stresses. In this research, melatonin was used to alleviate the adverse effects of oxidative stress induced by water deficit in Moldavian balm (Dracocephalum moldavica) plants and morpho-physiological traits were investigated. This experiment was conducted as a factorial arrangement based on completely randomized design with four replications. Treatments included foliar melatonin application at four levels 0 (distilled water), 50, 100 and 150 μM and drought stress 100 (control), 80, 60 and 40% of field capacity (FC). Higher levels of drought stress at 60% and 40% FC, caused the reduction of plant height, shoot fresh and dry weight, root length, root fresh and dry weight, photosynthetic pigments and protein content. Increased amount of soluble sugar content, malondialdehyde content and lipoxygenase activity, non-enzyme antioxidants (including flavonoid, polyphenol compounds and anthocyanin), phenylalanine ammonia-lyase and polyphenol oxidase enzymes activities were also observed at 60% and 40% FC. Melatonin at 100 µM improved morphological parameters, photosynthetic pigments and protein content under moderate and severe drought stress. The obtained results suggested that foliar application of 100 μM melatonin also alleviated oxidative burst and malondialdehyde production in Moldavian balm plant under moderate and severe drought stress probably through regulation of secondary metabolism and the enzymes activity of phenylalanine ammonia-lyase and polyphenol oxidase.

Overexpression of a Wheat Aquaporin Gene, TdPIP2;1, Enhances Salt and Drought Tolerance in Transgenic Durum Wheat cv. Maali

In this study, we generated transgenic durum wheat cv. Maali overexpressing the wheat plasma membrane aquaporin TdPIP2;1 gene under the control of PrTdPIP2;1 promoter or under the constitutive PrCaMV35S promoter. Histochemical analysis of the fusion PrTdPIP2;1::TdPIP2;1::GusA in wheat plants showed that the β-glucuronidase (GUS) activity was detected in the leaves, stems and roots of stably transformed wheat T3 plants. Our results showed that transgenic wheat lines overexpressing the TdPIP2;1 gene exhibited improved germination rates and biomass production and retained low Na+ and high K+ concentrations in their shoots under high salt and osmotic stress conditions. In a long-term study under greenhouse conditions on salt or drought stress, transgenic TdPIP2;1 lines produced filled grains, whereas wild-type (WT) plants either died at the vegetative stage under salt stress or showed drastically reduced grain filling under drought stress. Performing real time RT-PCR experiments on wheat plants transformed with the fusion PrTdPIP2;1::GusA, we showed an increase in the accumulation of GusA transcripts in the roots of plants challenged with salt and drought stress. Study of the antioxidant defence system in transgenic wheat TdPIP2;1 lines showed that these lines induced the antioxidative enzymes Catalase (CAT) and Superoxide dismutase (SOD) activities more efficiently than the WT plants, which is associated with lower malondialdehyde and hydrogen peroxide contents. Taken together, these results indicate the high potential of the TdPIP2;1 gene for reducing water evaporation from leaves (water loss) in response to water deficit through the lowering of transpiration per unit leaf area (stomatal conductance) and engineering effective drought and salt tolerance in transgenic TdPIP2;1 lines.

Distinctive phytohormonal and metabolic profiles of Arabidopsis thaliana and Eutrema salsugineum under similar soil drying

Arabidopsis and Eutrema show similar stomatal sensitivity to drying soil. In Arabidopsis, larger metabolic adjustments than in Eutrema occurred, with considerable differences in the phytohormonal responses of the two species. Although plants respond to soil drying via a series of concurrent physiological and molecular events, drought tolerance differs greatly within the plant kingdom. While Eutrema salsugineum (formerly Thellungiella salsuginea) is regarded as more stress tolerant than its close relative Arabidopsis thaliana, their responses to soil water deficit have not previously been directly compared. To ensure a similar rate of soil drying for the two species, daily soil water depletion was controlled to 5-10% of the soil water content. While partial stomatal closure occurred earlier in Arabidopsis (Day 4) than Eutrema (from Day 6 onwards), thereafter both species showed similar stomatal sensitivity to drying soil. However, both targeted and untargeted metabolite analysis revealed greater response to drought in Arabidopsis than Eutrema. Early peaks in foliar phytohormone concentrations and different sugar profiles between species were accompanied by opposing patterns in the bioactive cytokinin profiles. Untargeted analysis showed greater metabolic adjustment in Arabidopsis with more statistically significant changes in both early and severe drought stress. The distinct metabolic responses of each species during early drought, which occurred prior to leaf water status declining, seemed independent of later stomatal closure in response to drought. The two species also showed distinct water usage, with earlier reduction in water consumption in Eutrema (Day 3) than Arabidopsis (Day 6), likely reflecting temporal differences in growth responses. We propose Arabidopsis as a promising model to evaluate the mechanisms responsible for stress-induced growth inhibition under the mild/moderate soil drying that crop plants are typically exposed to.

Comprehensive metabolomic and proteomic analysis in biochemical metabolic pathways of rice spikes under drought and submergence stress

Drought and submergence are the main adverse factors affecting plant growth and yield formation in parts of China, especially in the Yangtze River region. In this study, T1 (drought duration: 10 d), T2 (submergence duration: 8 d) and CK (control) treatments were applied. This work aimed to study the changes in metabolic pathways of rice under drought and submergence stress during the panicle differentiation stage. The identification and analysis of differential metabolites and differentially expressed proteins functions indicate that drought and submergence mainly promoted the energy metabolism pathway, carbon fixation in photosynthetic organism pathway, carbohydrate metabolic process, and reactive oxygen species (ROS) metabolic process functions. Under drought stress, the inhibition of photosynthetic rate is mainly through stomatal conductance restriction, and flavonoid pathway regulates the metabolic process of ROS. Under submergence stress, the electron transfer chain was destroyed to inhibit the photosynthetic rate, and the antioxidant system was activated to regulate the metabolism of ROS. The changes in related enzymes or proteins in metabolic regulatory networks are analyzed, which will be conducive to understanding the response mechanism of rice drought and submergence more deeply and provide a scientific basis for rice drought and submergence prevention and mitigation, and the breeding of drought- and submergence-resistant varieties.

Ammonium uptake and metabolism alleviate PEG-induced water stress in rice seedlings

Ammonium (NH₄⁺) can enhance the water stress induced drought tolerance of rice seedlings in comparison to nitrate (NO₃^-) nutrition. To investigate the mechanism involved in nitrogen (N) uptake, N metabolism and transcript abundance of associated genes, a hydroponic experiment was conducted in which different N sources were supplied to seedlings growing under water stress. Compared to nitrate, ammonium prevented water stress-induced biomass, leaf SPAD and photosynthesis reduction to a significantly larger extent. Water stress significantly increased root nitrate reductase (NR) and nitrite reductase (NiR) activities, but decreased leaf NiR and glutamate synthetase (GS) activities under NO₃^- supply, causing lower nitrate content in roots and higher in leaves. In contrast, under NH₄⁺ supply root GS and glutamine oxoglutarate aminotransferase (GOGAT) activities were significantly decreased under water stress, but remained higher in leaves, compared to NO₃^- treatment, which was beneficial for the transport and assimilation of ammonium in leaves. ¹⁵N tracing assays demonstrated that rice ¹⁵N uptake rate and accumulation were significant reduced under water stress, but were higher in plants supplied with NH₄⁺ than with NO₃^-. Therefore, the formers showed higher leaf soluble sugar, proline and amino acids contents, and in turn, associated with a higher photosynthesis rate and biomass accumulation. Most genes related to NO₃^- uptake and reduction in roots and leaves were down-regulated; however, two ammonium transporter genes closely related to NH₄⁺ uptake (AMT1;2 and AMT1;3) were up-regulated in response to water stress. Overall, our findings suggest that ammonium supply alleviated waters tress in rice seedlings, mainly by increasing root NH₄⁺ uptake and leaf N metabolism.

Integrating transcriptomic techniques and k-means clustering in metabolomics to identify markers of abiotic and biotic stress in Medicago truncatula

INTRODUCTION

Nitrogen-fixing legumes are invaluable crops, but are sensitive to physical and biological stresses. Whilst drought and infection from the soil-borne pathogen Fusarium oxysporum have been studied individually, their combined effects have not been widely investigated.

OBJECTIVES

We aimed to determine the effect of combined stress using methods usually associated with transcriptomics to detect metabolic differences between treatment groups that could not be identified by more traditional means, such as principal component analysis and partial least squares discriminant analysis.

METHODS

Liquid chromatography-high resolution mass spectrometry data from the root and leaves of model legume Medicago truncatula were analysed using Gaussian Process 2-Sample Test, k-means cluster analysis and temporal clustering by affinity propagation.

RESULTS

Metabolic differences were detected: we identified known stress markers, including changes in concentration for sucrose and citric acid, and showed that combined stress can exacerbate the effect of drought. Changes in roots were found to be smaller than those in leaves, but differences due to Fusarium infection were identified. The transfer of sucrose from leaves to roots can be seen in the time series using transcriptomic techniques with the metabolomics time series. Other metabolite concentrations that change as a result of treatment include phosphoric acid, malic acid and tetrahydroxychalcone.

CONCLUSIONS

Probing metabolomic data with transcriptomic tools provides new insights and could help to identify resilient plant varieties, thereby increasing future crop yield and improving food security.

Comparative physiological and proteomic analyses reveal different adaptive strategies by Cymbidium sinense and C. tracyanum to drought

A terrestrial orchid, Cymbidium sinense appears to utilizes "remedy strategy", while an epiphytic orchid, C. tracyanum , employs a "precaution strategy" to drought stress based on morphological, physiological and proteomic analysis. Drought condition influences plant growth and productivity. Although the mechanism by which plants adapt to this abiotic stress has been studied extensively, the water-adaptive strategies of epiphytes grown in water-limited habitats remain undefined. Here, root and leaf anatomies, dynamic changes in physiological and proteomic responses during periods of drought stress and recovery studied in an epiphytic orchid (Cymbidium tracyanum) and a terrestrial orchid (C. sinense) to investigate their strategies for coping with drought. Compared with C. sinense, C. tracyanum showed stronger drought-resistant adaptive characteristics to drought because its leaves had more negative water potential at turgor loss point and roots had higher proportion of velamen radicum thickness. Although both species demonstrated quick recovery of photosynthesis after stress treatment, they differed in physiological and proteomic responses. We detected and functionally characterized 103 differentially expressed proteins in C. sinense and 104 proteins in C. tracyanum. These proteins were mainly involved in carbon and energy metabolism, photosynthesis, and defense responses. The up-regulated expression of plastid fibrillin may have contributed to the marked accumulation of jasmonates only in stressed C. sinense, while ferredoxin-NADP reductase up-regulation was only found in C. tracyanum which possibly related to the stimulation of cyclic electron flow that is linked with photoprotection. These physiological and proteomic performances suggest distinct adaptive strategies to drought stress between C. sinense (remedy strategy) and C. tracyanum (precaution strategy). Our findings may help improve our understanding about the ecological adaptation of epiphytic orchids.

Dissecting the proteome dynamics of the salt stress induced changes in the leaf of diploid and autotetraploid Paulownia fortunei

Exposure to high salinity can trigger acclimation in many plants. Such an adaptative response is greatly advantageous for plants and involves extensive reprogramming at the molecular level. Acclimation allows plants to survive in environments that are prone to increasing salinity. In this study, diploid and autotetraploid Paulownia fortunei seedlings were used to detect alterations in leaf proteins in plants under salt stress. Up to 152 differentially abundant proteins were identified by Multiplex run iTRAQ-based quantitative proteomic and LC-MS/MS methods. Bioinformatics analysis suggested that P. fortunei leaves reacted to salt stress through a combination of common responses, such as induced metabolism, signal transduction, and regulation of transcription. This study offers a better understanding of the mechanisms of salt tolerance in P. fortunei and provides a list of potential target genes that could be engineered for salt acclimation in plants, especially trees.

Approaches in modulating proline metabolism in plants for salt and drought stress tolerance: Phytohormones, mineral nutrients and transgenics

Major abiotic stress factors such as salt and drought adversely affect important physiological processes and biochemical mechanisms and cause severe loss in crop productivity worldwide. Plants develop various strategies to stand healthy against these stress factors. The accumulation of proline (Pro) is one of the striking metabolic responses of plants to salt and drought stress. Pro biosynthesis and signalling contribute to the redox balance of cell under normal and stressful conditions. However, literature is meager on the sustainable strategies potentially fit for modulating Pro biosynthesis and production in stressed plants. Considering the recent literature, this paper in its first part overviews Pro biosynthesis and transport in plants and also briefly highlights the significance of Pro in plant responses to salt and drought stress. Secondly, this paper discusses mechanisms underlying the regulation of Pro metabolism in salt and drought-exposed plant via phytohormones, mineral nutrients and transgenic approaches. The outcome of the studies may give new opportunities in modulating Pro metabolism for improving plant tolerance to salt and drought stress and benefit sustainable agriculture.

Starch as a determinant of plant fitness under abiotic stress

Contents 943 I. 943 II. 944 III. 945 IV. 945 V. 948 VI. 949 950 References 950 SUMMARY: Abiotic stresses, such as drought, high salinity and extreme temperatures, pose one of the most important constraints to plant growth and productivity in many regions of the world. A number of investigations have shown that plants, including several important crops, remobilize their starch reserve to release energy, sugars and derived metabolites to help mitigate the stress. This is an essential process for plant fitness with important implications for plant productivity under challenging environmental conditions. In this Tansley insight, we evaluate the current literature on starch metabolism in response to abiotic stresses, and discuss the key enzymes involved and how they are regulated.

Metabolomic approach reveals the biochemical mechanisms underlying drought stress tolerance in thyme

Thyme as a perennial herb has been recognized globally for its antimicrobial, antiseptic and spasmolytic effects. In this investigation, we have used non-targeted metabolite and volatile profiling combined with the morpho-physiological parameters in order to understand the responses at the metabolite and physiological level in drought sensitive and tolerant thyme plant populations. The results at the metabolic level identified the significantly affected metabolites. Significant metabolites belonging to different chemical classes consisting amino acids, carbohydrates, organic acids and lipids have been compared in tolerant and sensitive plants. These compounds may take a role through mechanisms including osmotic adjustment, ROS scavenging, cellular components protection and membrane lipid changes, hormone inductions in which the key metabolites were proline, betain, mannitol, sorbitol, ascorbate, jasmonate, unsaturated fatty acids and tocopherol. Regarding with volatile profiling, sensitive plants showed an increased-then-decreased trend at major terpenes apart from alpha-cubebene and germacrene-D. In contrast, tolerant populations had unchanged terpenes during the water stress period with an elevation at last day. These results suggesting that the two populations are employing different strategies. The combination of metabolite profiling and physiological parameters assisted to understand precisely the mechanisms of plant response at volatile metabolome level.

Drought stress tolerance strategies revealed by RNA-Seq in two sorghum genotypes with contrasting WUE

BACKGROUND

Drought stress is the major environmental stress that affects plant growth and productivity. It triggers a wide range of responses detectable at molecular, biochemical and physiological levels. At the molecular level the response to drought stress results in the differential expression of several metabolic pathways. For this reason, exploring the subtle differences in gene expression of drought sensitive and drought tolerant genotypes enables the identification of drought-related genes that could be used for selection of drought tolerance traits. Genome-wide RNA-Seq technology was used to compare the drought response of two sorghum genotypes characterized by contrasting water use efficiency.

RESULTS

The physiological measurements carried out confirmed the drought sensitivity of IS20351 and the drought tolerance of IS22330 genotypes, as previously studied. The expression of drought-related genes was more abundant in the drought sensitive genotype IS20351 compared to the tolerant genotype IS22330. Under drought stress Gene Ontology enrichment highlighted a massive increase in transcript abundance in the sensitive genotype IS20351 in "response to stress" and "abiotic stimulus", as well as for "oxidation-reduction reaction". "Antioxidant" and "secondary metabolism", "photosynthesis and carbon fixation process", "lipids" and "carbon metabolism" were the pathways most affected by drought in the sensitive genotype IS20351. In addition, genotype IS20351 showed a lower constitutive expression level of "secondary metabolic process" (GO:0019748) and "glutathione transferase activity" (GO:000004364) under well-watered conditions.

CONCLUSIONS

RNA-Seq analysis proved to be a very useful tool to explore differences between sensitive and tolerant sorghum genotypes. Transcriptomics analysis results supported all the physiological measurements and were essential to clarify the tolerance of the two genotypes studied. The connection between differential gene expression and physiological response to drought unequivocally revealed the drought tolerance of genotype IS22330 and the strategy adopted to cope with drought stress.

Selenium (Se) improves drought tolerance in crop plants--a myth or fact?

Climate change has emerged as one of the most complex challenges of the 21st century and has become an area of interest in the past few decades. Many countries of the world have become extremely vulnerable to the impacts of climate change. The scarcity of water is a serious concern for food security of these countries and climate change has aggravated the risks of extreme events like drought. Oxidative stress, caused by a variety of active oxygen species formed under drought stress, damages many cellular constituents, such as carbohydrates, lipids, nucleic acids and proteins, which ultimately reduces plant growth, respiration and photosynthesis. Se has become an element of interest to many biologists owing to its physiological and toxicological importance. It plays a beneficial role in plants by enhancing growth, reducing damage caused by oxidative stress, enhancing chlorophyll content under light stress, stimulating senesce to produce antioxidants and improving plant tolerance to drought stress by regulating water status. Researchers have adopted different strategies to evaluate the role of selenium in plants under drought stress. Some of the relevant work available regarding the role of Se in alleviating adverse effect of drought stress is discussed in this paper.

Drought-Induced Responses of Physiology, Metabolites, and PR Proteins in Triticum aestivum

The impact of severe drought stress (13% soil moisture) on the physiological responses, metabolic profile, and pathogenesis-related (PR) proteins in wheat above- and below-ground biomass after 20 days of treatment was studied. Drought depleted growth, assimilation pigments, and majority of free amino acids in the shoots (but proline increased considerably, +160%). On the contrary, root growth parameters were elevated, and free amino acids did not decrease, indicating investment of metabolites into the growth of roots under water deficiency. Mineral nutrients were only slightly influenced. Profiling of pathogenesis-related (PR) proteins revealed that chitinases (EC 3.2.1.14) and glucanases (EC 3.2.1.39) were activated in wheat by drought. Individual isoforms and their activity were rather stimulated under drought, especially in shoots. The expression of selected genes is in agreement with enzymatic data and suggests an organ (tissue) specific- and opposing behavior of these two types of defense components in drought-stressed wheat. Metabolic analyses at the level of phenolics showed an increase in the free and bound fraction of phenolic acids almost exclusively in the shoots and flavonoid isoorientin increased considerably: protective action against oxidative stress and dehydration of the leaves seems to be the main reason for this finding. The role of PR proteins and phenolics in drought-stressed tissue is discussed.

Simultaneous effects of leaf irradiance and soil moisture on growth and root system architecture of novel wheat genotypes: implications for phenotyping

Plants in the field are exposed to varying light and moisture. Agronomic improvement requires knowledge of whole-plant phenotypes expressed in response to simultaneous variation in these essential resources. Most phenotypes, however, have been described from experiments where resources are varied singularly. To test the importance of varying shoot and root resources for phenotyping studies, sister pre-breeding lines of wheat were phenotyped in response to independent or simultaneous exposure to two light levels and soil moisture profiles. The distribution and architecture of the root systems depended strongly on the moisture of the deeper soil layer. For one genotype, roots, specifically lateral roots, were stimulated to grow into moist soil when the upper zone was well-watered and were inhibited by drier deep zones. In contrast, the other genotype showed much less plasticity and responsiveness to upper moist soil, but maintained deeper penetration of roots into the dry layer. The sum of shoot and root responses was greater when treated simultaneously to low light and low soil water, compared to each treatment alone, suggesting the value of whole plant phenotyping in response to multiple conditions for agronomic improvement. The results suggest that canopy management for increased irradiation of leaves would encourage root growth into deeper drier soil, and that genetic variation within closely related breeding lines may exist to favour surface root growth in response to irrigation or in-season rainfall.

Global Synthesis of Drought Effects on Food Legume Production

Food legume crops play important roles in conservation farming systems and contribute to food security in the developing world. However, in many regions of the world, their production has been adversely affected by drought. Although water scarcity is a severe abiotic constraint of legume crops productivity, it remains unclear how the effects of drought co-vary with legume species, soil texture, agroclimatic region, and drought timing. To address these uncertainties, we collected literature data between 1980 and 2014 that reported monoculture legume yield responses to drought under field conditions, and analyzed this data set using meta-analysis techniques. Our results showed that the amount of water reduction was positively related with yield reduction, but the extent of the impact varied with legume species and the phenological state during which drought occurred. Overall, lentil (Lens culinaris), groundnut (Arachis hypogaea), and pigeon pea (Cajanus cajan) were found to experience lower drought-induced yield reduction compared to legumes such as cowpea (Vigna unguiculata) and green gram (Vigna radiate). Yield reduction was generally greater when legumes experienced drought during their reproductive stage compared to during their vegetative stage. Legumes grown in soil with medium texture also exhibited greater yield reduction compared to those planted on soil of either coarse or fine texture. In contrast, regions and their associated climatic factors did not significantly affect legume yield reduction. In the face of changing climate, our study provides useful information for agricultural planning and research directions for development of drought-resistant legume species to improve adaptation and resilience of agricultural systems in the drought-prone regions of the world.

Potential use of phytocystatins in crop improvement, with a particular focus on legumes

Phytocystatins are a well-characterized class of naturally occurring protease inhibitors that function by preventing the catalysis of papain-like cysteine proteases. The action of cystatins in biotic stress resistance has been studied intensively, but relatively little is known about their functions in plant growth and defence responses to abiotic stresses, such as drought. Extreme weather events, such as drought and flooding, will have negative impacts on the yields of crop plants, particularly grain legumes. The concepts that changes in cellular protein content and composition are required for acclimation to different abiotic stresses, and that these adjustments are achieved through regulation of proteolysis, are widely accepted. However, the nature and regulation of the protein turnover machinery that underpins essential stress-induced cellular restructuring remain poorly characterized. Cysteine proteases are intrinsic to the genetic programmes that underpin plant development and senescence, but their functions in stress-induced senescence are not well defined. Transgenic plants including soybean that have been engineered to constitutively express phytocystatins show enhanced tolerance to a range of different abiotic stresses including drought, suggesting that manipulation of cysteine protease activities by altered phytocystatin expression in crop plants might be used to improve resilience and quality in the face of climate change.

Redox proteomics and physiological responses in Cistus albidus shrubs subjected to long-term summer drought followed by recovery

The interaction between enzymatic and non-enzymatic antioxidants, endogenous levels of ABA and ABA-GE, the rapid recuperation of photosynthetic proteins under re-watering as well the high level of antioxidant proteins in previously drought-stressed plants under re-watering conditions, will contribute to drought resistance in plants subjected to a long-term drought stress under Mediterranean field conditions. This work provides an overview of the mechanisms of Cistus albidus acclimation to long-term summer drought followed by re-watering in Mediterranean field conditions. To better understand the molecular mechanisms of drought resistance in these plants, a proteomic study using 2-DE and MALDI-TOF/TOF MS/MS was performed on leaves from these shrubs. The analysis identified 57 differentially expressed proteins in water-stressed plants when contrasted to well watered. Water-stressed plants showed an increase, both qualitatively and quantitatively, in HSPs, and downregulation of photosynthesis and carbon metabolism enzymes. Under drought conditions, there was considerable upregulation of enzymes related to redox homeostasis, DHA reductase, Glyoxalase, SOD and isoflavone reductase. However, upregulation of catalase was not observed until after re-watering was carried out. Drought treatment caused an enhancement in antioxidant defense responses that can be modulated by ABA, and its catabolites, ABA-GE, as well as JA. Furthermore, quantification of protein carbonylation was shown to be a useful marker of the relationship between water and oxidative stress, and showed that there was only moderate oxidative stress in C. albidus plants subjected to water stress. After re-watering plants recovered although the levels of ABA-GE and antioxidant enzymes still remain higher than in well-watered plants. We expect that our results will provide new data on summer acclimation to drought stress in Mediterranean shrubs.

Moderate drought causes dramatic floral transcriptomic reprogramming to ensure successful reproductive development in Arabidopsis

BACKGROUND

Drought is a major constraint that leads to extensive losses to agricultural yield worldwide. The potential yield is largely determined during inflorescence development. However, to date, most investigations on plant response to drought have focused on vegetative development. This study describes the morphological changes of reproductive development and the comparison of transcriptomes under various drought conditions.

RESULTS

The plants grown were studied under two drought conditions: minimum for successful reproduction (45-50% soil water content, moderate drought, MD) and for survival (30-35%, severe drought, SD). MD plants can produce similar number of siliques on the main stem and similar number of seeds per silique comparing with well-water plants. The situation of SD plants was much worse than MD plants. The transcriptomes of inflorescences were further investigated at molecular level using microarrays. Our results showed more than four thousands genes with differential expression under severe drought and less than two thousand changed under moderate drought condition (with 2-fold change and q-value < 0.01). We found a group of genes with increased expression as the drought became more severe, suggesting putative adaptation to the dehydration. Interestingly, we also identified genes with alteration only under the moderate but not the severe drought condition, indicating the existence of distinct sets of genes responsive to different levels of water availability. Further cis-element analyses of the putative regulatory sequences provided more information about the underlying mechanisms for reproductive responses to drought, suggesting possible novel candidate genes that protect those developing flowers under drought stress.

CONCLUSIONS

Different pathways may be activated in response to moderate and severe drought in reproductive tissues, potentially helping plant to maximize its yield and balance the resource consumption between vegetative and reproductive development under dehydration stresses.

A better energy allocation of absorbed light in photosystem II and less photooxidative damage contribute to acclimation of Arabidopsis thaliana young leaves to water deficit

Water deficit stress promotes excitation pressure and photooxidative damage due to an imbalance between light capture and energy use. Young leaves (YL) of Arabidopsis thaliana plants acclimate better to the onset of water deficit (OnsWD) than do mature leaves (ML). To obtain a better understanding of this differential response, we evaluated whether YL and ML of A. thaliana exposed to the OnsWD, mild water deficit (MiWD) and moderate water deficit (MoWD), show differences in their photosynthetic performance, and whether photosynthetic acclimation correlates with leaf developmental stage. Water deficit (WD) resulted in greater photooxidative damage in ML compared to YL, but the latter could not be protected under the OnsWD or MiWD, but only under MoWD. YL of A. thaliana with signs of photosynthetic acclimation under MoWD retained higher maximum quantum yield (Fv/Fm) and decreased reactive oxygen species (ROS) formation. YL under MoWD, show a reduced excitation pressure and a better balance between light capture and photochemical energy use, which contributed to their photoprotection, but only under low light intensity (LL, 130μmolphotonsm(-2)s(-1)) and not under high light (HL, 1200μmolphotonsm(-2)s(-1)). In conclusion, leaf developmental stage was correlated with photo-oxidative damage and a differential allocation of absorbed light energy in photosystem II (PSII) of Arabidopsis leaves under WD.

The low energy signaling network

Stress impacts negatively on plant growth and crop productivity, caicultural production worldwide. Throughout their life, plants are often confronted with multiple types of stress that affect overall cellular energy status and activate energy-saving responses. The resulting low energy syndrome (LES) includes transcriptional, translational, and metabolic reprogramming and is essential for stress adaptation. The conserved kinases sucrose-non-fermenting-1-related protein kinase-1 (SnRK1) and target of rapamycin (TOR) play central roles in the regulation of LES in response to stress conditions, affecting cellular processes and leading to growth arrest and metabolic reprogramming. We review the current understanding of how TOR and SnRK1 are involved in regulating the response of plants to low energy conditions. The central role in the regulation of cellular processes, the reprogramming of metabolism, and the phenotypic consequences of these two kinases will be discussed in light of current knowledge and potential future developments.

Osmotic stress alters the balance between organic and inorganic solutes in flax (Linum usitatissimum)

Flax (Linum usitatissimum) is grown for its oil and its fiber. This crop, cultivated in temperate regions, has seen a renewed interest due to the presence of abundant molecules of interest for many applications. Little information is available about the behavior of flax during osmotic stress; yet this is considered a major stress that causes significant yield losses in most crops. To control the presence of this stress better, flax behavior was investigated following the application of osmotic stress and the response was examined by applying increasing concentrations of PEG 8000. This resulted in the reorganization of 32 metabolites and 6 mineral ions in the leaves. The analysis of these two types of solute highlighted the contrasting behavior between a higher metabolite content (particularly fructose, glucose and proline) and a decrease in mineral ions (especially nitrate and potassium) following PEG treatment. However, this reorganization did not lead to a greater accumulation of solutes, with the total amount remaining unchanged in leaves during osmotic stress.

Development-specific responses to drought stress in Aleppo pine (Pinus halepensis Mill.) seedlings

Aleppo pine (Pinus halepensis Mill.) is a pioneer species, highly competitive due to exceptional resistance to drought. To investigate the stress resistance in the first and second year of development, a steady-state drought experiment was implemented. Photosynthesis (A(net)), stomatal conductance and transpiration (E) were measured on three different sampling dates together with phloem soluble sugars, amino acids and non-structural proteins. Needle ascorbic acid (AsA) and reactive oxygen species were measured to evaluate the seedlings' drought stress condition in the final sampling. Drought impaired A(net) and E by 35 and 31%, respectively, and increased AsA levels up to 10-fold, without significant impact on the phloem metabolites. Phloem sugars related to temperature fluctuations rather than soil moisture and did not relate closely to A(net) levels. Sugars and proteins decreased between the second and third sampling date by 56 and 61%, respectively, and the ratio of sugars to amino acids decreased between the first and third sampling by 81%, while A(net) and water-use efficiency (A(net)/E) decreased only in the older seedlings. Although gas exchange was higher in the older seedlings, ascorbic acid and phloem metabolites were higher in the younger seedlings. It was concluded that the drought stress responses depended significantly on developmental stage, and research on the physiology of Aleppo pine regeneration should focus more on temperature conditions and the duration of drought than its severity.

Source-to-sink transport of sugar and regulation by environmental factors

Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.

Phenotyping common beans for adaptation to drought

Common beans (Phaseolus vulgaris L.) originated in the New World and are the grain legume of greatest production for direct human consumption. Common bean production is subject to frequent droughts in highland Mexico, in the Pacific coast of Central America, in northeast Brazil, and in eastern and southern Africa from Ethiopia to South Africa. This article reviews efforts to improve common bean for drought tolerance, referring to genetic diversity for drought response, the physiology of drought tolerance mechanisms, and breeding strategies. Different races of common bean respond differently to drought, with race Durango of highland Mexico being a major source of genes. Sister species of P. vulgaris likewise have unique traits, especially P. acutifolius which is well adapted to dryland conditions. Diverse sources of tolerance may have different mechanisms of plant response, implying the need for different methods of phenotyping to recognize the relevant traits. Practical considerations of field management are discussed including: trial planning; water management; and field preparation.

Effects of soil water and nitrogen availability on photosynthesis and water use efficiency of Robinia pseudoacacia seedlings

The efficient use of water and nitrogen (N) to promote growth and increase yield of fruit trees and crops is well studied. However, little is known about their effects on woody plants growing in arid and semiarid areas with limited water and N availability. To examine the effects of water and N supply on early growth and water use efficiency (WUE) of trees on dry soils, one-year-old seedlings of Robinia pseudoacacia were exposed to three soil water contents (non-limiting, medium drought, and severe drought) as well as to low and high N levels, for four months. Photosynthetic parameters, leaf instantaneous WUE (WUEi) and whole tree WUE (WUEb) were determined. Results showed that, independent of N levels, increasing soil water content enhanced the tree transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), maximum net assimilation rate (Amax), apparent quantum yield (AQY), the range of photosynthetically active radiation (PAR) due to both reduced light compensation point and enhanced light saturation point, and dark respiration rate (Rd), resulting in a higher net photosynthetic rate (Pn) and a significantly increased whole tree biomass. Consequently, WUEi and WUEb were reduced at low N, whereas WUEi was enhanced at high N levels. Irrespective of soil water availability, N supply enhanced Pn in association with an increase of Gs and Ci and a decrease of the stomatal limitation value (Ls), while Tr remained unchanged. Biomass and WUEi increased under non-limiting water conditions and medium drought, as well as WUEb under all water conditions; but under severe drought, WUEi and biomass were not affected by N application. In conclusion, increasing soil water availability improves photosynthetic capacity and biomass accumulation under low and high N levels, but its effects on WUE vary with soil N levels. N supply increased Pn and WUE, but under severe drought, N supply did not enhance WUEi and biomass.

Regulation of glutamine synthetase isoforms in two differentially drought-tolerant rice (Oryza sativa L.) cultivars under water deficit conditions

KEY MESSAGE : The regulation of GS isoforms by WD was organ specific. Two GS isoforms i.e. OsGS1;1 and OsGS2 were differentially regulated in IR-64 (drought-sensitive) and Khitish (drought-tolerant) cultivars of rice. Water deficit (WD) has adverse effect on rice (Oryza sativa L.) and acclimation requires essential reactions of primary metabolism to continue. Rice plants utilize ammonium as major nitrogen source, which is assimilated into glutamine by the reaction of Glutamine synthetase (GS, EC 6.3.1.2). Rice plants possess one gene (OsGS2) for chloroplastic GS2 and three genes (OsGS1;1, OsGS1;2 and OsGS1;3) for cytosolic GS1. Here, we report the effect of WD on regulation of GS isoforms in drought-sensitive (cv. IR-64) and drought-tolerant (cv. Khitish) rice cultivars. Under WD, total GS activity in root and leaf decreased significantly in IR-64 seedlings in comparison to Khitish seedlings. The reduced GS activity in IR-64 leaf was mainly due to decrease in GS2 activity, which correlated with decrease in corresponding transcript and polypeptide contents. GS1 transcript and polypeptide accumulated in leaf during WD, however, GS1 activity was maintained at a constant level. Total GS activity in stem of both the varieties was insensitive to WD. Among GS1 genes, OsGS1;1 expression was differently regulated by WD in the two rice varieties. Its transcript accumulated more abundantly in IR-64 leaf than in Khitish leaf. Following WD, OsGS1;1 mRNA level in stem and root tissues declined in IR-64 and enhanced in Khitish. A steady OsGS1;2 expression patterns were noted in leaf, stem and root of both the cultivars. Results suggest that OsGS2 and OsGS1;1 expression may contribute to drought tolerance of Khitish cultivar under WD conditions.

Water stress and aphid feeding differentially influence metabolite composition in Arabidopsis thaliana (L.)

Little is known about how drought stress influences plant secondary metabolite accumulation and how this affects plant defense against different aphids. We therefore cultivated Arabidopsis thaliana (L.) plants under well-watered, drought, and water-logged conditions. Two aphid species were selected for this study: the generalist Myzus persicae (Sulzer) and the crucifer specialist Brevicoryne brassicae (L.). Metabolite concentrations in the phloem sap, which influence aphid growth, changed particularly under drought stress. Levels of sucrose and several amino acids, such as glutamic acid, proline, isoleucine, and lysine increased, while concentrations of 4-methoxyindol-3-ylmethyl glucosinolate decreased. M. persicae population growth was highest on plants under drought stress conditions. However, B. brassicae did not profit from improved phloem sap quality under drought stress and performed equally in all water treatments. Water stress and aphids generally had an opposite effect on the accumulation of secondary metabolites in the plant rosettes. Drought stress and water-logging led to increased aliphatic glucosinolate and flavonoid levels. Conversely, aphid feeding, especially of M. persicae, reduced levels of flavonoids and glucosinolates in the plants. Correspondingly, transcript levels of aliphatic biosynthetic genes decreased after feeding of both aphid species. Contrary to M. persicae, drought stress did not promote population growth of B. brassicae on these plants. The specialist aphid induced expression of CYP79B2, CYP79B3, and PAD3 with corresponding accumulation of indolyl glucosinolates and camalexin. This was distinct from M. persicae, which did not elicit similarly strong camalexin accumulation, which led to the hypothesis of a specific defense adaptations against the specialist aphid.

Interaction of proline, sugars, and anthocyanins during photosynthetic acclimation of Arabidopsis thaliana to drought stress

The relationships among photosynthetic acclimation, proline (Pro), soluble sugar (SS), and anthocyanin (An) accumulation in Arabidopsis thaliana leaves to the onset of drought stress (OnDS), mild (MiDS) and moderate drought stress (MoDS), were evaluated. As leaf water content (LWC) decreased, metabolic concentrations (Pro, SS, and An) increased and were negatively and significantly correlated with LWC. Thus, these metabolites may have an important role in the acclimation process to drought stress (DS). No correlations among Pro, SS and An accumulation with the quantum efficiency of PSII photochemistry (Φ(PSII)) and the excitation pressure (1-q(P)) were observed under DS. This implies that, while metabolites increased in a drought-dependent way, PSII activity did not decrease in the same pattern. Our results indicated that, under MoDS, A. thaliana leaves were able to maintain oxidative compounds such as malondialdeyde, an end product of lipid peroxidation, within the range of control leaves, and to cope with oxidative damage, as was evident by the decreased excitation pressure (1-q(P)) and similar (ns difference) Φ(PSII) to that of control leaves. In addition, a statistically significant increased accumulation of Pro, SS and An was recorded only under MoDS compared to controls. The better PSII functioning of MoDS Arabidopsis leaves may reflect the greater capacity of these leaves to undertake key metabolic adjustments, including increased Pro, SS and An accumulation, to maintain a higher antioxidant protection and a better balance between light capture and energy use.