Progressive Water Deficit Research Articles

Responses of Leaf Expansion, Plant Transpiration and Leaf Senescence of Different Soybean (Glycine max. (L.) Merr.) Genotypes to Soil Water Deficit

ABSTRACTThe responses of eco‐physiological processes such as leaf expansion, plant transpiration and senescence to soil water deficit have been reported to be genotype‐dependent in different crops. To study such responses in soybean (Glycine max. (L.) Merr.), a 2‐year (2017 and 2021) outdoor pot experiment was carried out on the Heliaphen automated phenotyping platform at INRAE in Toulouse (France). Six soybean cultivars (Sultana‐MG 000, ES Pallador‐MG I, Isidor‐MG I, Santana‐MG I/II, Blancas‐MG II and Ecudor‐MG II) belonging to four maturity groups (MG) commonly grown in Europe were subjected to progressive soil water deficit from the reproductive stage R1 for 17 and 23 days in 2017 and 2021, respectively. The fraction of transpirable soil water (FTSW) was used as an indicator of soil water deficit. Non‐linear regression was used to calculate FTSWt, that is, the FTSW threshold for which the rate of the eco‐physiological process in stressed plants starts to diverge from a reference value. According to FTSWt, the three eco‐physiological processes showed significant differences in sensitivity to water deficit: leaf expansion exhibits the highest sensitivity and the widest range (FTSWt: 0.44–0.93), followed by plant transpiration (FTSWt: 0.17–0.56), with leaf senescence showing the narrowest range (FTSWt: 0.05–0.16). Among six cultivars, regarding leaf expansion, Cvs Santana (FTSWt = 0.48 in 2017; FTSWt = 0.44 in 2021), Blancas (FTSWt = 0.51 in 2017; FTSWt = 0.48 in 2021) and Ecudor (FTSWt = 0.46 in 2017; FTSWt = 0.52 in 2021) in late MGs (I/II to II) exhibited higher tolerance to soil drying. Conversely, the cv. Sultana in the earliest MG (000) showed the highest sensitivity (FTSWt = 0.91 in 2017; FTSWt = 0.93 in 2021) to water deficit. However, concerning the FTSWt values for plant transpiration (0.17–0.56 in 2017; 0.19–0.31 in 2021) and senescence (0.05–0.16 in 2017; 0.06–0.16 in 2021), their range did not demonstrate a correlated trend with the MG. In addition, a negative linear correlation was observed between values of FTSWt of normalised leaf expansion at the whole‐plant level (NLE) and specific leaf area (SLA) measured on irrigated plants for both years. This suggests that genotypes with high values of SLA could be associated with higher tolerance of leaf expansion to soil water deficit. Such a non‐destructive phenotyping method under outdoor conditions could bring new information to variety testing process and provide paths for integrating genotypic variability into crop growth models used for simulating soybean eco‐physiological responses to water deficit across the plant, field and even regional scales.

TIP1;1 expression could modulate the recovery of stomatal opening during rehydration in Sorghum bicolor

Stomatal conductance (gs) takes longer to recover after drought when compared to leaf water potential or leaf water content (RWC). Aquaporins, known for transporting water through membranes, could modulate gs recovery. Using Sorghum bicolor, we tested whether members of the plasma membrane (PIP) and tonoplast (TIP) intrinsic aquaporin subfamilies could influence gs after a 20-day drought. Potted plants under soil field capacity (control), severe water deficit (SWD; 30% (m/m) soil water content), and progressive severe water deficit (PSWD; water withheld until maximum stress) were used. Soil (Ψsoil), predawn (ΨPD), and midday (ΨMD) leaf water potentials, photochemical, and gas exchange parameters were measured during drought and 12 days of recovery. After 17 days of drought, gs of SWD and PSWD was 4-times lower than control, and it took 6 days to recover. ΨPD, ΨMD, and RWC, however, recovered after 24 h. SbPIP1;2, SbPIP2;5, and SbTIP1;1 were all down-regulated on the day of maximum stress, but only SbTIP1;1 showed consistent alleviation of its down-regulation as gs recovered. SbTIP1;1 expression was positively correlated with gs, leaf transpiration, and hydraulic conductivity (KL), but only in SWD plants. The slow gs recovery seems to be associated with the alleviation of SbTIP1;1 down-regulation as rehydration progresses.

Unravelling the responses of different apple varieties to water constraints by continuous field thermal monitoring

This research aimed at analyzing the response of apple tree varieties subjected to soil water deficit and atmospheric drought in a field phenotyping platform located in the Mediterranean area. The main assumption of the study was that seasonal and daily stomatal behavior can be monitored by continuous measurement of canopy surface temperature (Ts) as a proxy of stomatal closure. To achieve the study objectives, thermal monitoring of 6 pre-commercial apple varieties was simultaneously carried out throughout one season by nadir-oriented thermo-radiometers placed 1.50 m over the tree top canopy. Two water regimes were applied to each variety during a 4-week summer period: normal irrigation (WW) vs progressive water deficit (WS). The maximum difference in Ts between water regimes was recorded daily between 11:00 and 14:20 GMT, with an earlier closure of stomata in WS trees. During the day, a more negative stem water potential (Ψstem) and a higher diurnal Ts (+1° to +2 °C) were observed on WS trees, resulting in a significant limitation of fruit growth. Tree water stress was caused by both edaphic and atmospheric droughts, in the medium and short terms respectively, with inter-varietal and inter-regime differences highlighting distinct stomatal closure behaviors. Results suggest that some of the varieties studied are well adapted to stressful summer conditions, as long as irrigation needs are met, while other varieties show a particular sensitivity to the mid-day evaporative demand, which may limit their extension. Although these results are not comprehensive enough to predict the optimal performance of varieties under different stress scenarios, the proposed methodology allows to assess the dynamics of tree response to water constraints using non-invasive thermal sensors. It opens up new perspectives for the phenotyping of apple cultivars under abiotic stress, achievable through the quantified study of their transpiration flux in response to stress scenarios. These prospects will require further in planta measurements to dissect varietal differences.

A Simple and Accurate Method Based on a Water-Consumption Model for Phenotyping Soybean Genotypes under Hydric Deficit Conditions

Drought limits crop productivity and reduces yield stability. Drought tolerance as a selection criterion in breeding programs requires the development of high-throughput, precise, and low-cost phenotyping strategies. We developed a mathematical model, based on biological approaches, for evaluating soybean plants’ response to drought under controlled growth conditions. The model describes the kinetics of water consumption of a plant pot substrate system (PPS) with low sampling requirements. The model generated two parameters, t0.5 (time necessary for the PPS to reach half of the maximum amount of evapotranspirable water) and Gw(t0.5) (stomatal conductance [Gw] at t0.5), which determined the water- consumption curve of each genotype. An analysis of the kinetics of water consumption in response to a progressive water deficit in a biparental and breeding population was performed as a preliminary test of the model. A correspondence analysis between the t0.5 and Gw(t0.5) parameters with the genetic structure of the populations shows a genetic association. The phenotyping methodology presented in this work and drought susceptibility in field conditions are discussed based on previous results. This work could be useful for improving the selection of soybean genotypes in relation to their performance under drought conditions.

Increased Ascorbate Biosynthesis Does Not Improve Nitrogen Fixation Nor Alleviate the Effect of Drought Stress in Nodulated Medicago truncatula Plants.

Legume plants are able to establish nitrogen-fixing symbiotic relations with Rhizobium bacteria. This symbiosis is, however, affected by a number of abiotic constraints, particularly drought. One of the consequences of drought stress is the overproduction of reactive oxygen (ROS) and nitrogen species (RNS), leading to cellular damage and, ultimately, cell death. Ascorbic acid (AsA), also known as vitamin C, is one of the antioxidant compounds that plants synthesize to counteract this oxidative damage. One promising strategy for the improvement of plant growth and symbiotic performance under drought stress is the overproduction of AsA via the overexpression of enzymes in the Smirnoff-Wheeler biosynthesis pathway. In the current work, we generated Medicago truncatula plants with increased AsA biosynthesis by overexpressing MtVTC2, a gene coding for GDP-L-galactose phosphorylase. We characterized the growth and physiological responses of symbiotic plants both under well-watered conditions and during a progressive water deficit. Results show that increased AsA availability did not provide an advantage in terms of plant growth or symbiotic performance either under well-watered conditions or in response to drought.

Medicago sativa and Medicago truncatula Show Contrasting Root Metabolic Responses to Drought

Drought is an environmental stressor that affects crop yield worldwide. Understanding plant physiological responses to stress conditions is needed to secure food in future climate conditions. In this study, we applied a combination of plant physiology and metabolomic techniques to understand plant responses to progressive water deficit focusing on the root system. We chose two legume plants with contrasting tolerance to drought, the widely cultivated alfalfa Medicago sativa (Ms) and the model legume Medicago truncatula (Mt) for comparative analysis. Ms taproot (tapR) and Mt fibrous root (fibR) biomass increased during drought, while a progressive decline in water content was observed in both species. Metabolomic analysis allowed the identification of key metabolites in the different tissues tested. Under drought, carbohydrates, abscisic acid, and proline predominantly accumulated in leaves and tapRs, whereas flavonoids increased in fibRs in both species. Raffinose-family related metabolites accumulated during drought. Along with an accumulation of root sucrose in plants subjected to drought, both species showed a decrease in sucrose synthase (SUS) activity related to a reduction in the transcript level of SUS1, the main SUS gene. This study highlights the relevance of root carbon metabolism during drought conditions and provides evidence on the specific accumulation of metabolites throughout the root system.

Physiological, Biochemical and Yield-Component Responses of Solanum tuberosum L. Group Phureja Genotypes to a Water Deficit.

Water deficits are the major constraint in some potato-growing areas of the world. The effect is most severe at the tuberization stage, resulting in lower yield. Therefore, an assessment of genetic and phenotypic variations resulting from water deficits in Colombia germplasm is required to accelerate breeding efforts. Phenotypic variations in response to a water deficit were studied in a collection of Solanum tuberosum Group Phureja. A progressive water deficit experiment on the tuberization stage was undertaken using 104 genotypes belonging to the Working Collection of the Potato Breeding Program at the Universidad Nacional de Colombia. The response to water deficit conditions was assessed with the relative chlorophyll content (CC), maximum quantum efficiency of PSII (Fv/Fm), relative water content (RWC), leaf sugar content, tuber number per plant (TN) and tuber fresh weight per plant (TW). Principal Component Analysis (PCA) and cluster analysis were used, and the Drought Tolerance Index (DTI) was calculated for the variables and genotypes. The soluble sugar contents increased significantly under the deficit conditions in the leaves, with a weak correlation with yield under both water treatments. The PCA results revealed that the physiological, biochemical and yield-component variables had broad variation, while the yield-component variables more powerfully distinguished between the tolerant and susceptible genotypes than the physiological and biochemical variables. The PCA and cluster analysis based on the DTI revealed different levels of water deficit tolerance for the 104 genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying potato tolerance to water deficits.

English

Tartary buckwheat (Fagopyrum tataricum) is an important food crop that is widely adaptable to hostile environments. In this study the responses of two Tartary buckwheat genotypes: drought-susceptible Chuanqiao No. 1 (CQ) and drought-tolerant Jingqiao No. 2 (JQ) in terms of morphology, photosynthesis, physiology and yield to a progressive water deficit and recovery treatment (WD-R) were evaluated. Plants in the well-watered (WW) treatment were watered throughout the experiment. Compared to the WW treatment, water deficit in the WD-R treatment caused decreases in plant height, stem diameter, branch number, stem node number, biomass, seed number, soil water content (SWC), leaf relative water content (RWC), net photosynthesis rate (Pn), intercellular CO2 concentration, stomatal conductance (Gs), transpiration rate (Tr) and Fv/Fm in both CQ and JQ plants. Leaf wilting, malondialdehyde content, superoxide dismutase activity, peroxidase activity, initial fluorescence (F0) and root-to-shoot ratio were significantly increased under water stress in the WD-R treatment. Under the WD-R treatment, compared to CQ, JQ maintained higher RWC, SWC, Pn, Gs, WUE, Fv/Fm, plant height, branch number, stem node number, root biomass, stem biomass, leaf biomass, total biomass, root-to-shoot ratio, seed number per plant, and yield, but a lower Tr and F0. By correlation analysis, Gs was positively correlated with leaf RWC and SWC. These differential growth indexes, biochemical traits and physiological responses might be useful for understanding drought-tolerance genotypes that can grow under water-deficit conditions with minimum yield loss. © 2021 Friends Science Publishers

Regeneration of roots and seedlings from Eugenia involucrata seeds under water deficit conditions

Abstract: The aim of this study was to analyze the regenerative capacity of Eugenia involucrata seeds as a possible strategy to ensure the production of new seedlings when they are going through a period of water deficit. Progressive water deficit conditions over time (up to 60 days for seeds and 270 days for seedlings) and in intensity (up to -5 MPa for seeds and -10 MPa for seedlings) were simulated, and seedling regeneration was analyzed. The results showed that these seeds can survive even under the most extreme conditions (-5 MPa for 60 days) and some seedling tissues as well (-5 MPa for 270 days). Furthermore, roots and seedlings continued to develop from apparently necrotic tissue on the seed surface, showing that, when necessary, these seeds use their mechanism of formation of new roots and seedlings to ensure species survival under water stress conditions.

Systematic Investigation of the Effects of a Novel Protein Hydrolysate on the Growth, Physiological Parameters, Fruit Development and Yield of Grapevine (Vitis Vinifera L., cv Sauvignon Blanc) under Water Stress Conditions

In the last decade climate change has impacted viticulture and water deficit has become a major concern in fruit production. Many studies have been carried out to determine the grapevine response to environmental changes and to identify key genetic traits to be used in grapevine breeding. However, in order to better manage climate-related risks, novel viticultural practices are urgently needed. A promising solution for a more sustainable model of viticulture involves the use of biostimulants. In this study, the effectiveness of a novel biostimulant (APR®) belonging to the group of protein thermal hydrolysates was tested on grapevine plants subjected to progressive water deficit conditions. Our results showed that this compound applied to roots before imposing water deprivation mitigates the consequences of stress by sustaining the growth of the younger vegetative organs and limiting the extent of cell dehydration; this positive impact on the plant’s physiological state persisted during the recovery phase. Furthermore, at the end of the growing season, plants treated with the biostimulant, both in optimal water conditions and under water stress, exhibited a greater accumulation of biomass in the aerial part (6.8% and 21.3 %, respectively) and a higher berry diameter (3.4 % and 9.5 %, respectively). Additional work through field trials will be necessary to further substantiate these results and to translate this knowledge into specific practices that grape growers can easily adopt.

Physiological and PIP Transcriptional Responses to Progressive Soil Water Deficit in Three Mulberry Cultivars.

Although mulberry cultivars Wubu, Yu711, and 7307 display distinct anatomical, morphological, and agronomic characteristics under natural conditions, it remains unclear if they differ in drought tolerance. To address this question and elucidate the underlying regulatory mechanisms at the whole-plant level, 2-month old saplings of the three mulberry cultivars were exposed to progressive soil water deficit for 5 days. The physiological responses and transcriptional changes of PIPs in different plant tissues were analyzed. Drought stress led to reduced leaf relative water content (RWC) and tissue water contents, differentially expressed PIPs, decreased chlorophyll and starch, increased soluble sugars and free proline, and enhanced activities of antioxidant enzymes in all plant parts of the three cultivars. Concentrations of hydrogen peroxide (H2O2), superoxide anion (O2 •−), and malonaldehyde (MDA) were significantly declined in roots, stimulated in leaves but unaltered in wood and bark. In contrast, except the roots of 7307, soluble proteins were repressed in roots and leaves but induced in wood and bark of the three cultivars in response to progressive water deficit. These results revealed tissue-specific drought stress responses in mulberry. Comparing to cultivar Yu711 and 7307, Wubu showed generally slighter changes in leaf RWC and tissue water contents at day 2, corresponding well to the steady PIP transcript levels, foliar concentrations of chlorophyll, O2 •−, MDA, and free proline. At day 5, Wubu sustained higher tissue water contents in green tissues, displayed stronger responsiveness of PIP transcription, lower concentrations of soluble sugars and starch, lower foliar MDA, higher proline and soluble proteins, higher ROS accumulation and enhanced activities of several antioxidant enzymes. Our results indicate that whole-plant level responses of PIP transcription, osmoregulation through proline and soluble proteins and antioxidative protection are important mechanisms for mulberry to cope with drought stress. These traits play significant roles in conferring the relatively higher drought tolerance of cultivar Wubu and could be potentially useful for future mulberry improvement programmes.

Chlorophyll Fluorescence Kinetics May Be Useful to Identify Early Drought and Irrigation Effects on Photosynthetic Apparatus in Field-Grown Wheat

To assess the reliability and sensitivity of non-invasive optical methods to detect the early effects of water deficit in the field, we analyzed the time-series of non-invasive measurements obtained in a dry season in a representative collection of wheat genotypes grown in small-plot field trials, in non-irrigated and irrigated variants. Despite a progressive water deficit and significant yield loss, the measurements indicated very minor changes in chlorophyll content or canopy cover. This corresponded well to the insignificant differences in spectral reflectance normalized difference vegetation index (NDVI) values. On the other hand, we identified the significant and rapid response of fast fluorescence kinetics data following the onset of irrigation. Analysis of parameters showed the main effects of drought were associated with changes in the amplitude of the I–P phase of the OJIP transient, indicating changes at the level of photosystem I and beyond. Statistical analyses identified the integrative parameter performance index PItot as the most sensitive parameter, which well-reflects the differences in responses of the genotypes to water deficit. Our results suggest that focusing on photosynthetic functions detected by the rapid chlorophyll fluorescence records can provide more accurate information on the drought stress level, compared to the structural data obtained by absorbance or reflectance measurements.

Grafting cv. Grechetto Gentile Vines to New M4 Rootstock Improves Leaf Gas Exchange and Water Status as Compared to Commercial 1103P Rootstock

M4 is a relatively new rootstock that was selected for increased resilience of vineyards across hot regions where meteorological drought is often coupled to water scarcity. However, M4 has thus far been tested only against water-stress sensitive rootstocks. Against this backdrop, the aim of the present work is to examine the water status and gas exchange performances of vines grafted to M4 in comparison to those of vines grafted to a commercial stock that is drought-tolerant, 1103 Paulsen (1103P), under a progressive water deficit followed by re-watering. This study was undertaken on Grechetto Gentile, a cultivar that is renowned for its rather conservative water use (near-isohydric behavior). While fifty percent of both grafts were fully irrigated (WW), the remaining underwent progressive water stress by means of suspending irrigation (WS). Soil and leaf water status, as well as leaf gas exchanges, along with chlorophyll fluorescence, were followed daily from 1 day pre-stress (DOY 176) until re-watering (DOY 184). Final leaf area per vine, divided in main and lateral contribution, was also assessed. While 1103P grafted vines manifested higher water use under WW conditions, progressive stress evidenced a faster water depletion by 1103P, which also maintained slightly more negative midday leaf water potential (Ψleaf) as compared to M4 grafted plants. Daily gas exchange readings, as well as diurnal assessment performed at the peak of stress (DOY 183), also showed increased leaf assimilation rates (A) and water use efficiency (WUE) in vines grafted on M4, which were also less susceptible to photosynthetic downregulation. Dynamic of stomatal closure targeted at 90% reduction of leaf stomatal conductance showed a similar behavior among rootstocks since the above threshold was reached by both at Ψleaf of about −1.11 MPa. The same fractional reduction in leaf A was reached by vines grafted on M4 at a Ψleaf of −1.28 MPa vs. −1.10 MPa measured in 1103P, meaning that using M4 as a rootstock will postpone full stomatal closure. While mechanisms involved in improved CO2 uptake in M4-grafted vines under moderate-to-severe stress are still unclear, our data support the hypothesis that M4 might outscore the performance of a commercial drought-tolerant genotype (1103P) and can be profitably used as a tool to improve the resilience of vines to summer drought.

Physiological Beneficial Effect of Rhizophagus intraradices Inoculation on Tomato Plant Yield under Water Deficit Conditions

Increasing drought, under current climate change scenarios, will reduce the sustainability of tomato cultivation in the Mediterranean region. The present study evaluates the effect of Rhizophagus intraradices inoculation on tomato plant physiology and yield in response to progressive water deficit conditions. Two commercial products (Prod1 and Prod2) containing only R. intraradices were tested at two different concentrations (1% and 5% of the substrate volume) using three methods of inoculation: (a) mixed to substrate, (b) dissolved in water, (c) spread on seedlings root blocks before transplant. The highest mycorrhization of root fragments (F%) was found with Prod2 at 1% w/w at 40 days after sowing (DAS); this product was therefore used in a second experiment to inoculate tomato plants and test their physiological response to progressive water deficit induced withholding irrigation. Phenology, plant height, stem diameter, chlorophyll content and fluorescence, whole canopy gas exchange, biomass production and partitioning and phosphorus content were investigated in inoculated and not inoculated tomato plants under well-watered and water stressed conditions. Vegetative period and plant height were shorter in inoculated than in control plants; moreover, inoculation with R. intraradices increased fruit production by enhancing chlorophyll content under water stress condition, PS2 efficiency, ETR, Fv/Fm, net photosynthetic rate and whole canopy WUE.

Differential Gene Expression Pattern of Drought Responsive Transcription Factors in Chickpea: An Expressional Analysis

Chickpea (Cicer arietinum L.) is an important grain crop mainly grown in arid and semi-arid regions of the world. Drought is the major factor limiting chickpea growth and productivity. Transcription factors (TFs) genes have been reported as key regulators of drought tolerance in plants. In this study, we determined the relative gene expression of transcription factors of WRKY, DREB2A, and CarNAC3 in three weeks seedlings of tolerant (MCC537) and susceptible (MCC674) genotypes under progressive water deficit through semi-quantitative reverse transcriptase PCR (SqRT-PCR) method. Furthermore, results of SqRT-PCR were more confirmed by quantitative PCR (qPCR). Relative gene expression analysis of the selected genes using qPCR revealed different dehydration-responsive expression patterns. The expression of WRKY gene was significantly induced in both tolerant and sensitive genotypes under severe drought stress (at the last time point). Also, in tolerant genotype, DREB2A gene was approximately expressed three, five and fourfold higher than control plants at three times points, respectively. Moreover, the expression level of CarNAC3 gene in this genotype increased four and twofold higher compared to the relative control at 2 and 4 days after stress, respectively. However, the expression of these genes in the susceptible genotype was constant or decreased relative to the control. Furthermore, the CarNAC3 and DREB2A genes showed higher and more effective expression than the WRKY gene. Overall, the results demonstrated that these TFs may play an important role to improve drought tolerance and have a potential to facilitate molecular breeding and development of drought-tolerant chickpea varieties.

Transcriptomic analysis of a Sorghum bicolor landrace identifies a role for beta-alanine betaine biosynthesis in drought tolerance

Sorghum is indigenous to Africa and a remarkably drought tolerant cereal crop. In this study, the genetic response mechanisms involved in sorghum's tolerance to progressive water deficit and re-watering were investigated in a South African landrace (designated LR6), using cDNA microarrays comprising 35,899 transcript probes. Significant differential expression of 902 transcripts, including 128 transcripts with currently unknown functions, was altered in response to progressive water stress and re-watering. The modulated sorghum genes had homology to proteins involved in growth, regulation, and protection. Gene Ontology (GO) analysis identified significant enrichment of 26 genes involved in the ‘response to abiotic stimulus’ GO category during severe stress. The expression of two genes associated with beta(β)-alanine betaine biosynthesis was validated with quantitative RT-PCR. Importantly, the detection of β-alanine betaine in sorghum leaf extracts using NMR spectroscopy, and the significant increase in relative abundance during severe stress supports the microarray and qRT-PCR findings, thereby highlighting a role for β-alanine betaine biosynthesis in drought tolerance of sorghum. In future, crop improvement initiatives that consider metabolic engineering of the β-alanine betaine biosynthesis pathway should be explored.

Foliar application of gamma radiation processed chitosan triggered distinctive biological responses in sugarcane under water deficit stress conditions

Chitosan, being one of the most promising biological macromolecules, has an immense scope in agriculture to boost crop growth and defense responses. In this study, chitosan was exposed to gamma rays in order to obtain a low molecular weight derivative. Viscometric characterization showed a sharp decrease in molecular weight and FTIR based analysis confirmed retention of structural integrity of the polymer upon gamma irradiation. Assessments of various physiological and biochemical attributes were carried out on sugarcane plantlets that were subjected to progressive water deficit stress. The irradiated chitosan was found to differentially ameliorate water deficit stress tolerance against that of normal chitosan through positive modulation of various gas exchange parameters alongside significant improvement in relative tissue water content, SOD activity, soluble sugars and adenine energetics. Furthermore, application of irradiated chitosan significantly reduced cell membrane damage, lipid peroxidation, H2O2 and free-proline accumulations. This is the first report on the use of gamma irradiated chitosan to alleviate water deficit stress tolerance in sugarcane. Overall comparative assessments showed that differential plant responses were triggered upon foliar application of normal and gamma irradiated chitosan in sugarcane plants grown under water deficit stress conditions.

Application of anti-transpirants temporarily alleviates the inhibition of symbiotic nitrogen fixation in drought-stressed pea plants

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.

Comparative proteomics and gene expression analysis in Arachis duranensis reveal stress response proteins associated to drought tolerance

Peanut wild relatives (Arachis spp.) have high genetic diversity and are important sources of resistance to biotic and abiotic stresses. In this study, proteins were analyzed in root tissues of A. duranensis submitted to a progressive water deficit in soil and the differential abundance was compared to transcript expression profiles obtained by RNA-seq and qRT-PCR. Using a 2-DE approach, a total of 31 proteins were identified, most of which were associated with stress response and drought perception. These comprised a chitinase-2 (unique to stressed condition), an MLP-like protein, a glycine-rich protein DOT1-like, a maturase K and heat shock-related proteins (HSP70 – an isoform unique to the control, and HSP17.3). Other proteins unique to the control condition comprised a transcription initiation factor IIF subunit alpha-like protein, a SRPBCC ligand-binding domain superfamily protein, an Adenine phosphoribosyl transferase, a Leo1-like protein, a Cobalamine-independent methionine synthase and a Transmembrane emp24 domain-containing protein p24delta9-like. Correlation of mRNA expression and corresponding protein abundance was observed for 15 of the identified proteins, with genes encoding the majority of proteins (14) negatively regulated in stressed roots. Proteins identified in this study offer potential for the genetic improvement of cultivated peanut for drought tolerance. SignificanceThe comparison of protein abundance and corresponding transcript expression levels (RNA-seq and qRT-PCR) revealed that 15 of the identified proteins showed similar expression behavior, with the majority (14 proteins) negatively regulated in stressed roots. Chitinase-2 (Cht2) was the only protein with an upregulation behavior in all approaches. These proteins appear to play an important role in drought tolerance in A. duranensis and may be further explored in peanut genetic breeding programs.

Integrated drought responses of black poplar: how important is phenotypic plasticity?

Climate change is expected to increase drought frequency and intensity which will threaten plant growth and survival. In such fluctuating environments, perennial plants respond with hydraulic and biomass adjustments, resulting in either tolerant or avoidant strategies. Plants' response to stress relies on their phenotypic plasticity. The goal of this study was to explore physiology of young Populus nigra in the context of a time-limited and progressive water deficit in regard to their growth and stress response strategies. Fourteen French 1-year-old black poplar genotypes, geographically contrasted, were subjected to withholding water during 8 days until severe water stress. Water fluxes (i.e. leaf water potentials and stomatal conductance) were analyzed together with growth (i.e. radial and longitudinal branch growth, leaf senescence and leaf production). Phenotypic plasticity was calculated for each trait and response strategies to drought were deciphered for each genotype. Black poplar genotypes permanently were dealing with a continuum of adjusted water fluxes and growth between two extreme strategies, tolerance and avoidance. Branch growth, leaf number and leaf hydraulic potential traits had contrasted plasticities, allowing genotype characterization. The most tolerant genotype to water deficit, which maintained growth, had the lowest global phenotypic plasticity. Conversely, the most sensitive and avoidant genotype ceased growth until the season's end, had the highest plasticity level. All the remaining black poplar genotypes were close to avoidance with average levels of traits plasticity. These results underpinned the role of plasticity in black poplar response to drought and calls for its wider use into research on plants' responses to stress.