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We developed and characterized a paper-based microfluidic sensor for the on-site diagnosis of drought stress in plants. Proline was used as a biomarker for analyzing drought stress, which was extracted by a colorimetric method using the proline-ninhydrin reaction. Paper was used as the main sensor material for the on-site detection of proline as it is easily transportable and cost-effective. The paper-based sensor was fabricated using wax-printing and origami methods, and the sensor was precoated with ninhydrin to allow for easy and convenient on-site use. Furthermore, a sample-to-ninhydrin ratio of 1:2 was found to confer optimal sensitivity to the drought diagnosis sensor. The concentration of proline in a sample was quantified by red-green-blue analysis to determine the change in green color intensity levels in response to distinct proline concentrations, which were detected by the sensor. The limit of detection of proline using the devised sensor was 657 µM, and the green color intensity level decreased with increasing proline concentration. In addition, the sensor was validated in an experimental drought stress model with Arabidopsis and subjected to drought stress for 21 days, and the amount of proline detected was 10 mM. The devised paper-based microfluidic sensor highlights the possibility of the on-site evaluation of drought stress in plants with potential to be utilized in various agricultural areas in the future.

This paper integrates dendrochronological, demographic, and experimental perspectives to improve understanding of the response of white spruce ( Picea glauca (Moench) Voss) tree growth to climatic variability in interior Alaska. The dendrochronological analyses indicate that climate warming has led to widespread declines in white spruce growth throughout interior Alaska that have become more prevalent during the 20th century. Similarly, demographic studies show that white spruce tree growth is substantially limited by soil moisture availability in both mid- and late-successional stands. Interannual variability in tree growth among stands within a landscape exhibits greater synchrony than does growth of trees that occupy different landscapes, which agrees with dendrochronological findings that the responses depend on landscape position and prevailing climate. In contrast, the results from 18 years of a summer moisture limitation experiment showed that growth in midsuccessional upland stands was unaffected by moisture limitation and that moisture limitation decreased white spruce growth in floodplain stands where it was expected that growth would be less vulnerable because of tree access to river water. Taken together, the evidence from the different perspectives analyzed in this study clearly indicates that white spruce tree growth in interior Alaska is vulnerable to the effects of warming on plant water balance.

International audience; Desert truffles are edible hypogeous fungi forming ectendomycorrhizal symbiosis with plants of Cistaceae family. Knowledge about the reproductive modes of these fungi and the molecular mechanisms driving the ectendomycorrhizal interaction is lacking. Genomes of the highly appreciated edible desert truffles Terfezia claveryi Chatin and Tirmania nivea Trappe have been sequenced and compared with other Pezizomycetes. Transcriptomes of T. claveryi × Helianthemum almeriense mycorrhiza from well-watered and drought-stressed plants, when intracellular colonizations is promoted, were investigated. We have identified the fungal genes related to sexual reproduction in desert truffles and desert-truffles-specific genomic and secretomic features with respect to other Pezizomycetes, such as the expansion of a large set of gene families with unknown Pfam domains and a number of species or desert-truffle-specific small secreted proteins differentially regulated in symbiosis. A core set of plant genes, including carbohydrate, lipid-metabolism, and defence-related genes, differentially expressed in mycorrhiza under both conditions was found. Our results highlight the singularities of desert truffles with respect to other mycorrhizal fungi while providing a first glimpse on plant and fungal determinants involved in ecto to endo symbiotic switch that occurs in desert truffle under dry conditions.

High-throughput and accurate measurements of plant traits facilitate identification of gene function. Along with recent advances in quantitative genomics, there is a growing need for precise quantification of multiple traits in plants. However, it is difficult continuously to quantify plant adaptive responses to environmental stress responses such as drought because multiple environmental factors are intricately involved in the phenotype. To solve this problem, we developed an automatic phenotyping system for evaluating the growth responses of individual Arabidopsis plants to a wide range of environmental conditions. The RIKEN Integrated Plant Phenotyping System (RIPPS) controls soil moisture for single plants by automatically weighing and watering 120 continuously rotating pots under controlled light, humidity and temperature growth conditions. RIPPS also records individual rosette size and expansion rate by photographing plants every 2 h. We used RIPPS to establish phenotype evaluation methods for Arabidopsis growth response and water use efficiency under various water conditions, and analyzed the involvement of ABA metabolism in determining water use efficiency. We also used RIPPS to analyze salinity tolerance in Arabidopsis plants.

Overexpression of soybean GmDREB1 in wheat confers drought tolerance in the field and is associated with increased melatonin content, an increased root system, and delayed leaf senescence., Drought-response-element binding (DREB)-like transcription factors can significantly enhance plant tolerance to water stress. However, most research on DREB-like proteins to date has been conducted in growth chambers or greenhouses, so there is very little evidence available to support their practical use in the field. In this study, we overexpressed GmDREB1 from soybean in two popular wheat varieties and conducted drought-tolerance experiments across a range of years, sites, and drought-stress regimes. We found that the transgenic plants consistently exhibited significant improvements in yield performance and a variety of physiological traits compared with wild-type plants when grown under limited water conditions in the field, for example showing grain yield increases between 4.79–18.43%. Specifically, we found that the transgenic plants had reduced membrane damage and enhanced osmotic adjustment and photosynthetic efficiency compared to the non-transgenic controls. Three enzymes from the biosynthetic pathway of the phytohormone melatonin were up-regulated in the transgenic plants, and external application of melatonin was found to improve drought tolerance. Together, our results demonstrate the utility of transgenic overexpression of GmDREB1 to improve the drought tolerance of wheat in the field.

Glasshouse-based metabolic markers predict yield gap-based drought tolerance determined from multiseason and site field trials which could serve as a potential breeding tool for selecting drought-resilient crops., Water limits crop productivity, so selecting for a minimal yield gap in drier environments is critical to mitigate against climate change and land-use pressure. We investigated the responses of relative water content (RWC), stomatal conductance, chlorophyll content, and metabolites in flag leaves of commercial wheat (Triticum aestivum L.) cultivars to three drought treatments in the glasshouse and in field environments. We observed strong genetic associations between glasshouse-based RWC, metabolites, and yield gap-based drought tolerance (YDT; the ratio of yield in water-limited versus well-watered conditions) across 18 field environments spanning sites and seasons. Critically, RWC response to glasshouse drought was strongly associated with both YDT (r2=0.85, P

Highlight Osmotic stress enhances the rate of protein glycation and monosaccharide autoxidation is the main pathway., Among the environmental alterations accompanying oncoming climate changes, drought is the most important factor influencing crop plant productivity. In plants, water deficit ultimately results in the development of oxidative stress and accumulation of osmolytes (e.g. amino acids and carbohydrates) in all tissues. Up-regulation of sugar biosynthesis in parallel to the increasing overproduction of reactive oxygen species (ROS) might enhance protein glycation, i.e. interaction of carbonyl compounds, reducing sugars and α-dicarbonyls with lysyl and arginyl side-chains yielding early (Amadori and Heyns compounds) and advanced glycation end-products (AGEs). Although the constitutive plant protein glycation patterns were characterized recently, the effects of environmental stress on AGE formation are unknown so far. To fill this gap, we present here a comprehensive in-depth study of the changes in Arabidopsis thaliana advanced glycated proteome related to osmotic stress. A 3 d application of osmotic stress revealed 31 stress-specifically and 12 differentially AGE-modified proteins, representing altogether 56 advanced glycation sites. Based on proteomic and metabolomic results, in combination with biochemical, enzymatic and gene expression analysis, we propose monosaccharide autoxidation as the main stress-related glycation mechanism, and glyoxal as the major glycation agent in plants subjected to drought.

In plant cells, calcium-dependent protein kinases (CDPKs) are important sensors of Ca2+ flux resulting from various environmental stresses like cold, drought or salt stress. Previous genome sequence analysis and comparative studies in Arabidopsis (Arabidopsis thaliana L.) and rice (Oryza sativa L.) defined a multi-gene family of CDPKs. Here, we identified and characterised the CDPK gene complement of the model plant, barley (Hordeum vulgare L.). Comparative analysis encompassed phylogeny reconstruction based on newly available barley genome sequence, as well as established model genomes (e.g. O. sativa, A. thaliana, Brachypodium distachyon). Functional gene copies possessed characteristic CDPK domain architecture, including a serine/threonine kinase domain and four regulatory EF-hand motifs. In silico verification was followed by measurements of transcript abundance via real-time polymerase chain reaction (PCR). The relative expression of CDPK genes was determined in the vegetative growth stage under intensifying drought stress conditions. The majority of barley CDPK genes showed distinct changes in patterns of expression during exposure to stress. Our study constitutes evidence for involvement of the barley CDPK gene complement in signal transduction pathways relating to adaptation to drought. Our bioinformatics and transcriptomic analyses will provide an important foundation for further functional dissection of the barley CDPK gene family. Electronic supplementary material The online version of this article (doi:10.1007/s13353-016-0357-2) contains supplementary material, which is available to authorized users.

Highlight VaNAC26, a member of the NAC gene family from the wild species Vitis amurensis, plays an important role in drought tolerance by positively modulating jasmonic acid synthesis and enhancing the antioxidant system., The growth and fruit quality of grapevines are widely affected by abnormal climatic conditions such as water deficits, but many of the precise mechanisms by which grapevines respond to drought stress are still largely unknown. Here, we report that VaNAC26, a member of the NAC transcription factor family, was upregulated dramatically during cold, drought and salinity treatments in Vitis amurensis, a cold and drought-hardy wild Vitis species. Heterologous overexpression of VaNAC26 enhanced drought and salt tolerance in transgenic Arabidopsis. Higher activities of antioxidant enzymes and lower concentrations of H2O2 and O2 − were found in VaNAC26-OE lines than in wild type plants under drought stress. These results indicated that scavenging by reactive oxygen species (ROS) was enhanced by VaNAC26 in transgenic lines. Microarray-based transcriptome analysis revealed that genes related to jasmonic acid (JA) synthesis and signaling were upregulated in VaNAC26-OE lines under both normal and drought conditions. VaNAC26 showed a specific binding ability on the NAC recognition sequence (NACRS) motif, which broadly exists in the promoter regions of upregulated genes in transgenic lines. Endogenous JA content significantly increased in the VaNAC26-OE lines 2 and 3. Our data suggest that VaNAC26 responds to abiotic stresses and may enhance drought tolerance by transcriptional regulation of JA synthesis in Arabidopsis.

Highlight The relationship between an adenine isopentenyltransferase transgene, reactive oxygen species (ROS) content and the ROS-scavenging system, mechanistically contributing to improved root growth under drought stress in creeping bentgrass, is discussed., Drought stress limits root growth and inhibits cytokinin (CK) production. Increases in CK production through overexpression of isopentenyltransferase (ipt) alleviate drought damages to promote root growth. The objective of this study was to investigate whether CK-regulated root growth was involved in the alteration of reactive oxygen species (ROS) production and ROS scavenging capacity under drought stress. Wild-type (WT) creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) and a transgenic line (S41) overexpressing ipt ligated to a senescence-activated promoter (SAG12) were exposed to drought stress for 21 d in growth chambers. SAG12-ipt transgenic S41 developed a more extensive root system under drought stress compared to the WT. Root physiological analysis (electrolyte leakage and lipid peroxidation) showed that S41 roots exhibited less cellular damage compared to the WT under drought stress. Roots of SAG12-ipt transgenic S41 had significantly higher endogenous CK content than the WT roots under drought stress. ROS (hydrogen peroxide and superoxide) content was significantly lower and content of total and free ascorbate was significantly higher in S41 roots compared to the WT roots under drought stress. Enzymatic assays and transcript abundance analysis showed that superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase were significantly higher in S41 roots compared to the WT roots under drought stress. S41 roots also maintained significantly higher alternative respiration rates compared to the WT under drought stress. The improved root growth of transgenic creeping bentgrass may be facilitated by CK-enhanced ROS scavenging through antioxidant accumulation and activation of antioxidant enzymes, as well as higher alternative respiration rates when soil water is limited.

Modelling predicts that drought tolerance during reproductive development is important for higher yield potentials (up to 37%) and greater yield stability for wheat under future climate change in Europe., Drought stress during reproductive development could drastically reduce wheat grain number and yield, but quantitative evaluation of such an effect is unknown under climate change. The objectives of this study were to evaluate potential yield benefits of drought tolerance during reproductive development for wheat ideotypes under climate change in Europe, and to identify potential cultivar parameters for improvement. We used the Sirius wheat model to optimize drought-tolerant (DT) and drought-sensitive (DS) wheat ideotypes under a future 2050 climate scenario at 13 contrasting sites, representing major wheat growing regions in Europe. Averaged over the sites, DT ideotypes achieved 13.4% greater yield compared with DS, with higher yield stability. However, the performances of the ideotypes were site dependent. Mean yield of DT was 28–37% greater compared with DS in southern Europe. In contrast, no yield difference (≤1%) between ideotypes was found in north-western Europe. An intermediate yield benefit of 10–23% was found due to drought tolerance in central and eastern Europe. We conclude that tolerance to drought stress during reproductive development is important for high yield potentials and greater yield stability of wheat under climate change in Europe.

Highlight Automated imaging-based plant phenotyping combined with GC-MS-based metabolite profiling of four lentil accessions differing in their drought and salt tolerance shows common and specific responses and yields characteristic stress markers, Drought and salinity are among the major abiotic stresses which, often inter-relatedly, adversely affect plant growth and productivity. Plant stress responses depend on the type of stress, on its intensity, on the species, and also on the genotype. Different accessions of a species may have evolved different mechanisms to cope with stress and to complete their life cycles. This study is focused on lentil, an important Mediterranean legume with high quality protein for the human diet. The effects of salinity and drought on germination and early growth of Castelluccio di Norcia (CAST), Pantelleria (PAN), Ustica (UST), and Eston (EST) accessions were evaluated to identify metabolic and phenotypic traits related to drought and/or salinity stress tolerance. The results showed a relationship between imposed stresses and performance of the cultivars. According to germination frequencies, the accession ranking was as follows: NaCl resistant > susceptible, PAN > UST > CAST > EST; polyethylene glycol (PEG) resistant > susceptible, CAST > UST > EST > PAN. Seedling tolerance rankings were: NaCl resistant > susceptible, CAST ≈ UST > PAN ≈ EST; PEG resistant > susceptible, CAST > EST ≈ UST > PAN. Changes in the metabolite profiles, mainly quantitative rather than qualitative, were observed in the same cultivar in respect to the treatments, and among the cultivars under the same treatment. Metabolic differences in the stress tolerance of the different genotypes were related to a reduction in the levels of tricarboxylic acid (TCA) cycle intermediates. The relevant differences, between the most NaCl-tolerant genotype (PAN) and the most sensitive one (EST) were related to the decrease in the threonic acid level. Stress-specific metabolite indicators were also identified: ornithine and asparagine as markers of drought stress and alanine and homoserine as markers of salinity stress.

Key message QTL related to cooler canopy temperatures are associated with optimal root distribution whereby roots proliferate at depth under drought or near to surface under hot, irrigated conditions. Abstract Previous research using a bread wheat RIL population of the Seri/Babax cross showed that common QTL were associated with cooler canopies under both drought and heat-stressed conditions. A subset of RIL was grown under water-limited and hot-irrigated field environments to test how cooler canopies are related to root development. Eight sisters and the two parents were used in the study with genotypes grouped as COOL or HOT according to their respective QTL for canopy temperature and previous phenotypic data. Root mass production and residual available soil moisture were measured around anthesis at four depth profiles (from 0 to 120 cm depth). When considering different root profiles, there was a clear interaction of QTL with environment. Under water stress, the COOL genotypes showed a deeper root system allowing the extraction of 35 % more water from the 30–90 cm soil profile. The strategy under heat was to concentrate more roots at the surface, in the 0–60 cm soil layer where water was more available from surface irrigation. Since COOL genotypes showed better agronomic performance, it can be concluded that their QTL are associated with more optimal root distribution in accordance with water availability under the respective stresses. The study demonstrates the importance of root development under both water-limited and hot-irrigated environments, and shows a common genetic basis for adaptation to both stresses that appears to be associated with sensitivity of roots to proliferate where water is available in the soil profile.

Highlight The genetic variation of root system architecture in the A and B wheat genomes is described, providing the necessary knowledge ultimately to fine-tune the expression of the root system architecture., Optimization of root system architecture (RSA) traits is an important objective for modern wheat breeding. Linkage and association mapping for RSA in two recombinant inbred line populations and one association mapping panel of 183 elite durum wheat (Triticum turgidum L. var. durum Desf.) accessions evaluated as seedlings grown on filter paper/polycarbonate screening plates revealed 20 clusters of quantitative trait loci (QTLs) for root length and number, as well as 30 QTLs for root growth angle (RGA). Divergent RGA phenotypes observed by seminal root screening were validated by root phenotyping of field-grown adult plants. QTLs were mapped on a high-density tetraploid consensus map based on transcript-associated Illumina 90K single nucleotide polymorphisms (SNPs) developed for bread and durum wheat, thus allowing for an accurate cross-referencing of RSA QTLs between durum and bread wheat. Among the main QTL clusters for root length and number highlighted in this study, 15 overlapped with QTLs for multiple RSA traits reported in bread wheat, while out of 30 QTLs for RGA, only six showed co-location with previously reported QTLs in wheat. Based on their relative additive effects/significance, allelic distribution in the association mapping panel, and co-location with QTLs for grain weight and grain yield, the RSA QTLs have been prioritized in terms of breeding value. Three major QTL clusters for root length and number (RSA_QTL_cluster_5#, RSA_QTL_cluster_6#, and RSA_QTL_cluster_12#) and nine RGA QTL clusters (QRGA.ubo-2A.1, QRGA.ubo-2A.3, QRGA.ubo-2B.2/2B.3, QRGA.ubo-4B.4, QRGA.ubo-6A.1, QRGA.ubo-6A.2, QRGA.ubo-7A.1, QRGA.ubo-7A.2, and QRGA.ubo-7B) appear particularly valuable for further characterization towards a possible implementation of breeding applications in marker-assisted selection and/or cloning of the causal genes underlying the QTLs.

Summary Increased endogenous NO content modulates ROS accumulation and related antioxidant enzyme activities, osmolyte levels, and the expression of stress-responsive genes, such as AtPYL4/5, resulting in enhanced drought resistance in Arabidopsis., Nitric oxide (NO) is involved in plant responses to many environmental stresses. Transgenic Arabidopsis lines that constitutively express rat neuronal NO synthase (nNOS) were described recently. In this study, it is reported that the nNOS transgenic Arabidopsis plants displayed high levels of osmolytes and increased antioxidant enzyme activities. Transcriptomic analysis identified 601 or 510 genes that were differentially expressed as a consequence of drought stress or nNOS transformation, respectively. Pathway and gene ontology (GO) term enrichment analyses revealed that genes involved in photosynthesis, redox, stress, and phytohormone and secondary metabolism were greatly affected by the nNOS transgene. Several CBF genes and members of zinc finger gene families, which are known to regulate transcription in the stress response, were changed by the nNOS transgene. Genes regulated by both the nNOS transgene and abscisic acid (ABA) treatments were compared and identified, including those for two ABA receptors (AtPYL4 and AtPYL5). Moreover, overexpression of AtPYL4 and AtPYL5 enhanced drought resistance, antioxidant enzyme activity, and osmolyte levels. These observations increase our understanding of the role of NO in drought stress response in Arabidopsis.

Abscisic acid (ABA) is a phytohormone that plays important roles in the regulation of seed dormancy and adaptation to abiotic stresses. Previous work identified OsPYL/RCARs as functional ABA receptors regulating ABA-dependent gene expression in Oryza sativa. OsPYL/RCARs thus are considered to be good candidate genes for improvement of abiotic stress tolerance in crops. This work demonstrates that the cytosolic ABA receptor OsPYL/RCAR5 in O. sativa functions as a positive regulator of abiotic stress-responsive gene expression. The constitutive expression of OsPYL/RCAR5 in rice driven by the Zea mays ubiquitin promoter induced the expression of many stress-responsive genes even under normal growth conditions and resulted in improved drought and salt stress tolerance in rice. However, it slightly reduced plant height under paddy field conditions and severely reduced total seed yield. This suggests that, although exogenous expression of OsPYL/RCAR5 is able to improve abiotic stress tolerance in rice, fine regulation of its expression will be required to avoid deleterious effects on agricultural traits.

Highlight Plants use the alternative oxidase to modulate the rate of mitochondrial respiration in the light, maintaining chloroplast energy balance and hence optimizing photosynthesis under varied growth conditions., Mitochondria have a non-energy-conserving alternative oxidase (AOX) proposed to support photosynthesis, perhaps by promoting energy balance under varying growth conditions. To investigate this, wild-type (WT) Nicotiana tabacum were compared with AOX knockdown and overexpression lines. In addition, the amount of AOX protein in WT plants was compared with that of chloroplast light-harvesting complex II (LHCB2), whose amount is known to respond to chloroplast energy status. With increased growth irradiance, WT leaves maintained higher rates of respiration in the light (RL), but no differences in RL or photosynthesis were seen between the WT and transgenic lines, suggesting that, under non-stress conditions, AOX was not critical for leaf metabolism, regardless of growth irradiance. However, under drought, the AOX amount became an important determinant of RL, which in turn was an important determinant of chloroplast energy balance (measured as photosystem II excitation pressure, EP), and photosynthetic performance. In the WT, the AOX amount increased and the LHCB2 amount decreased with increased growth irradiance or drought severity. These changes in protein amounts correlated strongly, in opposing ways, with growth EP. This suggests that a signal deriving from the photosynthetic electron transport chain status coordinately controls the amounts of AOX and LHCB2, which then both contribute to maintaining chloroplast energy balance, particularly under stress conditions.

Responses to drought, heat, and combined stress were compared in tobacco (Nicotiana tabacum L.) plants ectopically expressing the cytokinin oxidase/dehydrogenase CKX1 gene of Arabidopsis thaliana L. under the control of either the predominantly root-expressed WRKY6 promoter or the constitutive 35S promoter, and in the wild type. WRKY6:CKX1 plants exhibited high CKX activity in the roots under control conditions. Under stress, the activity of the WRKY6 promoter was down-regulated and the concomitantly reduced cytokinin degradation coincided with raised bioactive cytokinin levels during the early phase of the stress response, which might contribute to enhanced stress tolerance of this genotype. Constitutive expression of CKX1 resulted in an enlarged root system, a stunted, dwarf shoot phenotype, and a low basal level of expression of the dehydration marker gene ERD10B. The high drought tolerance of this genotype was associated with a relatively moderate drop in leaf water potential and a significant decrease in leaf osmotic potential. Basal expression of the proline biosynthetic gene P5CSA was raised. Both wild-type and WRKY6:CKX1 plants responded to heat stress by transient elevation of stomatal conductance, which correlated with an enhanced abscisic acid catabolism. 35S:CKX1 transgenic plants exhibited a small and delayed stomatal response. Nevertheless, they maintained a lower leaf temperature than the other genotypes. Heat shock applied to drought-stressed plants exaggerated the negative stress effects, probably due to the additional water loss caused by a transient stimulation of transpiration. The results indicate that modulation of cytokinin levels may positively affect plant responses to abiotic stress through a variety of physiological mechanisms.

A wheat stay-green mutant, tasg1, was previously generated via mutation breeding of HS2, a common wheat cultivar (Triticum aestivum L.). Compared with wild-type (WT) plants, tasg1 exhibited delayed senescence indicated by the slower degradation of chlorophyll. In this study, the stability of proteins in thylakoid membranes was evaluated in tasg1 under drought stress compared with WT plants in the field as well as in seedlings in the laboratory. Drought stress was imposed by controlling irrigation and sheltering the plants from rain in the field, and by polyethylene glycol (PEG)-6000 in the laboratory. The results indicated that tasg1 plants could maintain higher Hill activity, actual efficiency (ΦPSII), maximal photochemical efficiency of PSII (Fv/Fm), and Ca(2+)-ATPase and Mg(2+)-ATPase activities than the WT plants under drought stress. Furthermore, the abundance of some polypeptides in thylakoid membranes of tasg1 was greater than that in the WT under drought stress. Expression levels of TaLhcb4 and TaLhcb6 were higher in tasg1 compared with the WT. Under drought stress, the accumulation of superoxide radical (O2·(-)) and hydrogen peroxide (H2O2) was lower in tasg1 compared with the WT not only at the senescence stage but also at the seedling stages. These results suggest greater functional stability of thylakoid membrane proteins in tasg1 compared with the WT, and the higher antioxidant competence of tasg1 may play an important role in the enhanced drought tolerance of tasg1.

Highlight Direct X-ray micro-imaging reveals localized xylem embolism under water stress conditions in the leaves of intact maize, with a specific spatial distribution of embolism in terms of xylem structure., The vulnerability of vascular plants to xylem embolism is closely related to their stable long-distance water transport, growth, and survival. Direct measurements of xylem embolism are required to understand what causes embolism and what strategies plants employ against it. In this study, synchrotron X-ray microscopy was used to non-destructively investigate both the anatomical structures of xylem vessels and embolism occurrence in the leaves of intact Zea mays (maize) plants. Xylem embolism was induced by water stress at various soil drying periods and soil water contents. X-ray images of dehydrated maize leaves showed that the ratio of gas-filled vessels to all xylem vessels increased with decreased soil water content and reached approximately 30% under severe water stress. Embolism occurred in some but not all vessels. Embolism in maize leaves was not strongly correlated with xylem diameter but was more likely to occur in the peripheral veins. The rate of embolism formation in metaxylem vessels was higher than in protoxylem vessels. This work has demonstrated that xylem embolism remains low in maize leaves under water stress and that there xylem has characteristic spatial traits of vulnerability to embolism.

Autophagy plays critical roles in plant responses to stress. In contrast to the wealth of information concerning the core process of plant autophagosome assembly, our understanding of the regulation of autophagy is limited. In this study, we demonstrated that transcription factor HsfA1a played a critical role in tomato tolerance to drought stress, in part through its positive role in induction of autophagy under drought stress. HsfA1a expression was induced by drought stress. Virus-induced HsfA1a gene silencing reduced while its overexpression increased plant drought tolerance based on both symptoms and membrane integrity. HsfA1a-silenced plants were more sensitive to endogenous ABA-mediated stomatal closure, while its overexpression lines were resistant under drought stress, indicating that phytohormone ABA did not play a major role in HsfA1a-induced drought tolerance. On the other hand, HsfA1a-silenced plants increased while its overexpression decreased the levels of insoluble proteins which were highly ubiquitinated under drought stress. Furthermore, drought stress induced numerous ATGs expression and autophagosome formation in wild-type plants. The expression of ATG10 and ATG18f, and the formation of autophagosomes were compromised in HsfA1a-silenced plants but were enhanced in HsfA1a-overexpressing plants. Both electrophoretic mobility shift assay and chromatin immunoprecipitation coupled with qPCR analysis revealed that HsfA1a bound to ATG10 and ATG18f gene promoters. Silencing of ATG10 and ATG18f reduced HsfA1a-induced drought tolerance and autophagosome formation in plants overexpressing HsfA1a. These results demonstrate that HsfA1a induces drought tolerance by activating ATG genes and inducing autophagy, which may promote plant survival by degrading ubiquitinated protein aggregates under drought stress.

Cytokinins (CKs) may be involved in the regulation of plant adaptation to drought stress. The objectives of the study were to identify proteomic changes in leaves and roots in relation to improved drought tolerance in transgenic creeping bentgrass (Agrostis stolonifera) containing a senescence-activated promoter (SAG12) and the isopentyl transferase (ipt) transgene that increases endogenous CK content. Leaves of SAG12-ipt bentgrass exhibited less severe senescence under water stress, as demonstrated by maintaining lower electrolyte leakage and lipid peroxidation, and higher photochemical efficiency (F(v)/F(m)), compared with the null transformant (NT) plants. SAG12-ipt plants had higher root/shoot ratios and lower lipid peroxidation in leaves under water stress than the NT plants. The suppression of drought-induced leaf senescence and root dieback in the transgenic plants was associated with the maintenance of greater antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase). The SAG12-ipt and NT plants exhibited differential protein expression patterns under well-watered and drought conditions in both leaves and roots. Under equivalent leaf water deficit (47% relative water content), SAG12-ipt plants maintained higher abundance of proteins involved in (i) energy production within both photosynthesis and respiration [ribulose 1,5-bisphosphate carboxylase (RuBisCO) and glyceraldehyde phosphate dehydrogenase (GAPDH)]; (ii) amino acid synthesis (methionine and glutamine); (iii) protein synthesis and destination [chloroplastic elongation factor (EF-Tu) and protein disulphide isomerases (PDIs)]; and (iv) antioxidant defence system (catalase and peroxidase) than the NT plants. These results suggest that increased endogenous CKs under drought stress may directly or indirectly regulate protein abundance and enzymatic activities involved in the above-mentioned metabolic processes, thereby enhancing plant drought tolerance.

Leaves of many evergreen angiosperm species turn red under high light during winter due to the production of anthocyanin pigments, while leaves of other species remain green. There is currently no explanation for why some evergreen species exhibit winter reddening while others do not. Conditions associated with low leaf water potentials (Psi) have been shown to induce reddening in many plant species. Because evergreen species differ in susceptibility to water stress during winter, it is hypothesized that species which undergo winter colour change correspond with those that experience/tolerate the most severe daily declines in leaf Psi during winter. Six angiosperm evergreen species which synthesize anthocyanin in leaves under high light during winter and five species which do not were studied. Field Psi, pressure/volume curves, and gas exchange measurements were derived in summer (before leaf colour change had occurred) and winter. Consistent with the hypothesis, red-leafed species as a group had significantly lower midday Psi in winter than green-leafed species, but not during the summer when all the leaves were green. However, some red-leafed species showed midday declines similar to those of green-leafed species, suggesting that low Psi alone may not induce reddening. Pressure-volume curves also provided some evidence of acclimation to more negative water potentials by red-leafed species during winter (e.g. greater osmotic adjustment and cell wall hardening on average). However, much overlap in these physiological parameters was observed as well between red and green-leafed species, and some of the least drought-acclimated species were red-leafed. No difference was observed in transpiration (E) during winter between red and green-leaved species. When data were combined, only three of the six red-leafed species examined appeared physiologically acclimated to prolonged drought stress, compared to one of the five green-leafed species. This suggests that drought stress alone is not sufficient to explain winter reddening in evergreen angiosperms.

The interaction of photosynthesis and respiration has been studied in vivo under conditions of limited water supply and after consecutive rewatering. The role of the alternative (v(alt)) and cytochrome (v(cyt)) pathways on drought stress-induced suppression of photosynthesis and during photosynthetic recovery was examined in the Nicotiana sylvestris wild type (WT) and the complex I-deficient CMSII mutant. Although photosynthetic traits, including net photosynthesis (A(N)), stomatal (g(s)) and mesophyll conductances (g(m)), as well as respiration (v(cyt) and v(alt)) differed between well-watered CMSII and WT, similar reductions of A(N), g(s), and g(m) were observed during severe drought stress. However, total respiration (V(t)) remained slightly higher in CMSII due to the still increased v(cyt) (to match ATP demand). v(alt) and maximum carboxylation rates remained almost unaltered in both genotypes, while in CMSII, changes in photosynthetic light harvesting (i.e. Chl a/b ratio) were detected. In both genotypes, photosynthesis and respiration were restored after 2 d of rewatering, predominantly limited by a delayed stomatal response. Despite complex I dysfunction and hence altered redox balance, the CMSII mutant seems to be able to adjust its photosynthetic machinery during and after drought stress to reduce photo-oxidation and to maintain the cell redox state and the ATP level.

Pearl millet, a key staple crop of the semi-arid tropics, is mostly grown in water-limited conditions, and improving its performance depends on how genotypes manage limited water resources. This study investigates whether the control of water loss under non-limiting water conditions is involved in the terminal drought tolerance of pearl millet. Two pairs of tolerant x sensitive pearl millet genotypes, PRLT 2/89-33-H77/833-2 and 863B-P2-ICMB 841-P3, and near-isogenic lines (NILs), introgressed with a terminal drought tolerance quantitative trait locus (QTL) from the donor parent PRLT 2/89-33 into H77/833-2 (NILs-QTL), were tested. Upon exposure to water deficit, transpiration began to decline at lower fractions of transpirable soil water (FTSW) in tolerant than in sensitive genotypes, and NILs-QTL followed the pattern of the tolerant parents. The transpiration rate (Tr, in g water loss cm(-2) d(-1)) under well-watered conditions was lower in tolerant than in sensitive parental genotypes, and the Tr of NILs-QTL followed the pattern of the tolerant parents. In addition, Tr measured in detached leaves (g water loss cm(-2) h(-1)) from field-grown plants of the parental lines showed lower Tr values in tolerant parents. Defoliation led to an increase in Tr that was higher in sensitive than in tolerant genotypes. The differences in Tr between genotypes was not related to the stomatal density. These results demonstrate that constitutive traits controlling leaf water loss under well-watered conditions correlate with the terminal drought tolerance of pearl millet. Such traits may lead to more water being available for grain filling under terminal drought.

Drought tolerance is a key trait for increasing and stabilizing barley productivity in dry areas worldwide. Identification of the genes responsible for drought tolerance in barley (Hordeum vulgare L.) will facilitate understanding of the molecular mechanisms of drought tolerance, and also facilitate the genetic improvement of barley through marker-assisted selection or gene transformation. To monitor the changes in gene expression at the transcriptional level in barley leaves during the reproductive stage under drought conditions, the 22K Affymetrix Barley 1 microarray was used to screen two drought-tolerant barley genotypes, Martin and Hordeum spontaneum 41-1 (HS41-1), and one drought-sensitive genotype Moroc9-75. Seventeen genes were expressed exclusively in the two drought-tolerant genotypes under drought stress, and their encoded proteins may play significant roles in enhancing drought tolerance through controlling stomatal closure via carbon metabolism (NADP malic enzyme, NADP-ME, and pyruvate dehydrogenase, PDH), synthesizing the osmoprotectant glycine-betaine (C-4 sterol methyl oxidase, CSMO), generating protectants against reactive-oxygen-species scavenging (aldehyde dehydrogenase,ALDH, ascorbate-dependent oxidoreductase, ADOR), and stabilizing membranes and proteins (heat-shock protein 17.8, HSP17.8, and dehydrin 3, DHN3). Moreover, 17 genes were abundantly expressed in Martin and HS41-1 compared with Moroc9-75 under both drought and control conditions. These genes were possibly constitutively expressed in drought-tolerant genotypes. Among them, seven known annotated genes might enhance drought tolerance through signalling [such as calcium-dependent protein kinase (CDPK) and membrane steroid binding protein (MSBP)], anti-senescence (G2 pea dark accumulated protein, GDA2), and detoxification (glutathione S-transferase, GST) pathways. In addition, 18 genes, including those encoding Delta(l)-pyrroline-5-carboxylate synthetase (P5CS), protein phosphatase 2C-like protein (PP2C), and several chaperones, were differentially expressed in all genotypes under drought; thus they were more likely to be general drought-responsive genes in barley. These results could provide new insights into further understanding of drought-tolerance mechanisms in barley.

Drought is considered to enhance susceptibility of Norway spruce (Picea abies) to infestations by the Eurasian spruce bark beetle (Ips typographus, Coleoptera: Curculionidae), although empirical evidence is scarce. We studied the impact of experimentally induced drought on tree water status and constitutive resin flow, and how physiological stress affects host acceptance and resistance. We established rain-out shelters to induce both severe (two full-cover plots) and moderate (two semi-cover plots) drought stress. In total, 18 sample trees, which were divided equally between the above treatment plots and two control plots, were investigated. Infestation was controlled experimentally using a novel 'attack box' method. Treatments influenced the ratios of successful and defended attacks, but predisposition of trees to infestation appeared to be mainly driven by variations in stress status of the individual trees over time. With increasingly negative twig water potentials and decreasing resin exudation, the defence capability of the spruce trees decreased. We provide empirical evidence that water-limiting conditions impair Norway spruce resistance to bark beetle attack. Yet, at the same time our data point to reduced host acceptance by I. typographus with more extreme drought stress, indicated by strongly negative pre-dawn twig water potentials.

MicroRNAs (miRNAs) are a class of small, non-coding regulatory RNAs that regulate gene expression by guiding target mRNA cleavage or translational inhibition in plants and animals. At present there is relatively little information regarding the role of miRNAs in the response to drought stress in maize. In this study, two small RNA libraries were sequenced, and a total of 11,973,711 and 14,326,010 raw sequences were generated from growing leaves of drought-tolerant and drought-sensitive maize seedlings, respectively. Further analysis identified 192 mature miRNAs, which include 124 known maize (zma) miRNAs and 68 potential novel miRNA candidates. Additionally, 167 target genes (259 transcripts) of known and novel miRNAs were predicted to be differentially expressed between two maize inbred lines. Of these, three novel miRNAs were up-regulated and two were down-regulated under drought stress. The expression of these five miRNAs and nine target genes was confirmed using quantitative reverse transcription PCR. The expression of three of the miRNAs and their putative target genes exhibited an inverse correlation, and expression analysis suggested that all five may play important roles in maize leaves. Finally, GO annotations of the target genes indicated a potential role in photosynthesis, may therefore contribute to the drought stress response. This study describes the identification and characterization of novel miRNAs that are the differentially expressed in drought-tolerant and drought-sensitive inbred maize lines. This provides the foundation for further investigation into the mechanism of miRNA function in response to drought stress in maize.

Highlight Altering root xylem developmental plasticity by increasing the number of vessels and decreasing their diameter enhances water uptake and reduces yield loss in soybean under water-limited conditions., We tested the hypothesis that increasing the number of metaxylem vessels would enhance the efficiency of water uptake in soybean (Glycine max) and decrease the yield gap in water-limited environments. A panel of 41 soybean accessions was evaluated in greenhouse, rainout shelter, and rain-fed field environments. The metaxylem number influenced the internal capture of CO2 and improved stomatal conductance, enhancing water uptake/use in soybeans exposed to stress during the reproductive stage. We determined that other root anatomical features, such as cortex cell area and the percentage of stele that comprised cortical cells, also affected seed yield under similar growth parameters. Seed yield was also impacted by pod retention rates under drought stress (24–80 pods/plant). We surmise that effective biomass allocation, that is, the transport of available photosynthates to floral structures at late reproductive growth stages (R6–R7), enables yield protection under drought stress. A mesocosm study of contrasting lines for yield under drought stress and root anatomical features revealed that increases in metaxylem number as an adaptation to drought in the high-yielding lines improved root hydraulic conductivity, which reduced the metabolic cost of exploring water in deeper soil strata and enhanced water transport. This allowed the maintenance of shoot physiological processes under water-limited conditions.

Summary In young and mature plants of the CAM species Agave angustifolia, the day/night pattern of CO2 exchange was highly conserved under a range of environmental conditions., Agaves exhibit the water-conserving crassulacean acid metabolism (CAM) photosynthetic pathway. Some species are potential biofuel feedstocks because they are highly productive in seasonally dry landscapes. In plants with CAM, high growth rates are often believed to be associated with a significant contribution of C3 photosynthesis to total carbon gain when conditions are favourable. There has even been a report of a shift from CAM to C3 in response to overwatering a species of Agave. We investigated whether C3 photosynthesis can contribute substantially to carbon uptake and growth in young and mature Agave angustifolia collected from its natural habitat in Panama. In well-watered plants, CO2 uptake in the dark contributed about 75% of daily carbon gain. This day/night pattern of CO2 exchange was highly conserved under a range of environmental conditions and was insensitive to intensive watering. Elevated CO2 (800 ppm) stimulated CO2 fixation predominantly in the light. Exposure to CO2-free air at night markedly enhanced CO2 uptake during the following light period, but CO2 exchange rapidly reverted to its standard pattern when CO2 was supplied during the subsequent 24h. Although A. angustifolia consistently engages in CAM as its principal photosynthetic pathway, its relatively limited photosynthetic plasticity does not preclude it from occupying a range of habitats, from relatively mesic tropical environments in Panama to drier habitats in Mexico.

Heat-stressed crops suffer dehydration, depressed growth, and a consequent decline in water productivity, which is the yield of harvestable product as a function of lifetime water consumption and is a trait associated with plant growth and development. Heat shock transcription factor (HSF) genes have been implicated not only in thermotolerance but also in plant growth and development, and therefore could influence water productivity. Here it is demonstrated that Arabidopsis thaliana plants with increased HSFA1b expression showed increased water productivity and harvest index under water-replete and water-limiting conditions. In non-stressed HSFA1b-overexpressing (HSFA1bOx) plants, 509 genes showed altered expression, and these genes were not over-represented for development-associated genes but were for response to biotic stress. This confirmed an additional role for HSFA1b in maintaining basal disease resistance, which was stress hormone independent but involved H₂O₂ signalling. Fifty-five of the 509 genes harbour a variant of the heat shock element (HSE) in their promoters, here named HSE1b. Chromatin immunoprecipitation-PCR confirmed binding of HSFA1b to HSE1b in vivo, including in seven transcription factor genes. One of these is MULTIPROTEIN BRIDGING FACTOR1c (MBF1c). Plants overexpressing MBF1c showed enhanced basal resistance but not water productivity, thus partially phenocopying HSFA1bOx plants. A comparison of genes responsive to HSFA1b and MBF1c overexpression revealed a common group, none of which harbours a HSE1b motif. From this example, it is suggested that HSFA1b directly regulates 55 HSE1b-containing genes, which control the remaining 454 genes, collectively accounting for the stress defence and developmental phenotypes of HSFA1bOx. ispartof: JOURNAL OF EXPERIMENTAL BOTANY vol:64 issue:11 pages:3467-3481 ispartof: location:England status: published

Several lipid-transfer proteins were reported to modulate the plant response to biotic stress; however, whether lipid-transfer proteins are also involved in abiotic stress remains unknown. This study characterized the function of a lipid-transfer protein, LTP3, during freezing and drought stress. LTP3 was expressed ubiquitously and the LTP3 protein was localized to the cytoplasm. A biochemical study showed that LTP3 was able to bind to lipids. Overexpression of LTP3 resulted in constitutively enhanced freezing tolerance without affecting the expression of CBFs and their target COR genes. Further analyses showed that LTP3 was positively regulated by MYB96 via the direct binding to the LTP3 promoter; consistently, transgenic plants overexpressing MYB96 exhibited enhanced freezing tolerance. This study also found that the loss-of-function mutant ltp3 was sensitive to drought stress, whereas overexpressing plants were drought tolerant, phenotypes reminiscent of myb96 mutant plants and MYB96-overexpressing plants. Taken together, these results demonstrate that LTP3 acts as a target of MYB96 to be involved in plant tolerance to freezing and drought stress.

Drought stress is a major factor limiting nitrogen fixation (NF) in crop production. However, the regulatory mechanism involved and the origin of the inhibition, whether local or systemic, is still controversial and so far scarcely studied in temperate forage legumes. Medicago truncatula plants were symbiotically grown with a split-root system and exposed to gradual water deprivation. Physiological parameters, NF activity, and amino acid content were measured. The partial drought treatment inhibited NF in the nodules directly exposed to drought stress. Concomitantly, in the droughted below-ground organs, amino acids accumulated prior to any drop in evapotranspiration (ET). It is concluded that drought exerts a local inhibition of NF and drives an overall accumulation of amino acids in diverse plant organs which is independent of the decrease in ET. The general increase in the majority of single amino acids in the whole plant questions the commonly accepted concept of a single amino acid acting as an N-feedback signal. This work was financed by the Spanish Ministry of Economy and Competitiveness (AGL 2011–23738 and AGL 2011-30386-C02-01). EG-Q is a holder of a PhD fellowship from the Public University of Navarre (735/2008). EL is a recipient of a Marie Curie International Outgoing Fellowship for Career Development (PIOF-GA-2009–253141).

Immediately after unfolding, cotyledons of the tropical platyopuntoid cactus, Opuntia elatior Mill., exhibited a C(3)-type diel CO(2) exchange pattern characterized by net CO(2) uptake in the light. Significant nocturnal increases in titratable acidity typical of crassulacean acid metabolism (CAM) were not detected at this early developmental stage. As cotyledons matured and the first cladode (flattened stem) developed, features of CAM were observed and the magnitude of CAM increased. Nonetheless, in well-watered seedlings up to 10 cm tall, C(3) photosynthetic CO(2) fixation in the light remained the major pathway of carbon fixation. Reduced soil water availability led to an up-regulation of net dark CO(2) fixation and greater nocturnal increases in tissue acidity, consistent with facultative CAM. These observations demonstrate that C(3) photosynthesis, drought-stress-related facultative CAM, and developmentally controlled constitutive CAM can all contribute to the early growth of O. elatior. The strong C(3) component and facultative CAM features expressed in young O. elatior contrast with mature plants in which obligate CAM is the major pathway of carbon acquisition.

Aluminium (Al) toxicity and drought are the two major abiotic stress factors limiting common bean production in the tropics. Using hydroponics, the short-term effects of combined Al toxicity and drought stress on root growth and Al uptake into the root apex were investigated. In the presence of Al stress, PEG 6000 (polyethylene glycol)-induced osmotic (drought) stress led to the amelioration of Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1. PEG 6000 (>> PEG 1000) treatment greatly decreased Al accumulation in the 1 cm root apices even when the roots were physically separated from the PEG solution using dialysis membrane tubes. Upon removal of PEG from the treatment solution, the root tips recovered from osmotic stress and the Al accumulation capacity was quickly restored. The PEG-induced reduction of Al accumulation was not due to a lower phytotoxic Al concentration in the treatment solution, reduced negativity of the root apoplast, or to enhanced citrate exudation. Also cell-wall (CW) material isolated from PEG-treated roots showed a low Al-binding capacity which, however, was restored after destroying the physical structure of the CW. The comparison of the Al(3+), La(3+), Sr(2+), and Rb(+) binding capacity of the intact root tips and the isolated CW revealed the specificity of the PEG 6000 effect for Al. This could be due to the higher hydrated ionic radius of Al(3+) compared with other cations (Al(3+) >> La(3+) > Sr(2+) > Rb(+)). In conclusion, the results provide circumstantial evidence that the osmotic stress-inhibited Al accumulation in root apices and thus reduced Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1 is related to the alteration of CW porosity resulting from PEG 6000-induced dehydration of the root apoplast.

A full-length drought-responsive gene Ccrboh, encoding the respiratory burst oxidase homologue (rboh), was cloned in Citrullus colocynthis, a very drought-tolerant cucurbit species. The robh protein, also named NADPH oxidase, is conserved in plants and animals, and functions in the production of reactive oxygen species (ROS). The Ccrboh gene accumulated in a tissue-specific pattern when C. colocynthis was treated with PEG, abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), or NaCl, while the homologous rboh gene did not show any change in C. lanatus var. lanatus, cultivated watermelon, during drought. Grafting experiments were conducted using C. colocynthis or C. lanatus as the rootstock or scion. Results showed that the rootstock significantly affects gene expression in the scion, and some signals might be transported from the root to the shoot. Ccrboh in C. colocynthis was found to function early during plant development, reaching high mRNA transcript levels 3 d after germination. The subcellular location of Ccrboh was investigated by transient expression of the 35S::Ccrboh::GFP fusion construct in protoplasts. The result confirmed that Ccrboh is a transmembrane protein. Our data suggest that Ccrboh might be functionally important during the acclimation of plants to stress and also in plant development. It holds great promise for improving drought tolerance of other cucurbit species.

Theobroma cacao (cacao) is cultivated in tropical climates and is exposed to drought stress. The impact of the endophytic fungus Trichoderma hamatum isolate DIS 219b on cacao's response to drought was studied. Colonization by DIS 219b delayed drought-induced changes in stomatal conductance, net photosynthesis, and green fluorescence emissions. The altered expression of 19 expressed sequence tags (ESTs) (seven in leaves and 17 in roots with some overlap) by drought was detected using quantitative real-time reverse transcription PCR. Roots tended to respond earlier to drought than leaves, with the drought-induced changes in expression of seven ESTs being observed after 7 d of withholding water. Changes in gene expression in leaves were not observed until after 10 d of withholding water. DIS 219b colonization delayed the drought-altered expression of all seven ESTs responsive to drought in leaves byor = 3 d, but had less influence on the expression pattern of the drought-responsive ESTs in roots. DIS 219b colonization had minimal direct influence on the expression of drought-responsive ESTs in 32-d-old seedlings. By contrast, DIS 219b colonization of 9-d-old seedlings altered expression of drought-responsive ESTs, sometimes in patterns opposite of that observed in response to drought. Drought induced an increase in the concentration of many amino acids in cacao leaves, while DIS 219b colonization caused a decrease in aspartic acid and glutamic acid concentrations and an increase in alanine and gamma-aminobutyric acid concentrations. With or without exposure to drought conditions, colonization by DIS 219b promoted seedling growth, the most consistent effects being an increase in root fresh weight, root dry weight, and root water content. Colonized seedlings were slower to wilt in response to drought as measured by a decrease in the leaf angle drop. The primary direct effect of DIS 219b colonization was promotion of root growth, regardless of water status, and an increase in water content which it is proposed caused a delay in many aspects of the drought response of cacao.

Phospholipase D (PLD) is involved in different plant processes, ranging from responses to abiotic and biotic stress to plant development. Phospholipase Dδ (PLDδ) is activated in dehydration and salt stress, producing the lipid second messenger phosphatidic acid. In this work we show that pldδ Arabidopsis mutants were more tolerant to severe drought than wild-type plants. PLDδ has been shown to be required for ABA regulation of stomatal closure of isolated epidermal peels. However, there was no significant difference in stomatal conductance at the whole plant level between wild-type and pldδ mutants. Since PLD hydrolyses structural phospholipids, then we looked at membrane integrity. Ion leakage measurements showed that during dehydration of leaf discs pldδ mutant has less membrane degradation compared to the wild-type. We further analyzed the mutants and showed that pldδ have higher mRNA levels of RAB18 and RD29A compared to wild-type plants under normal growth conditions. Transient expression of AtPLDδ in Nicotiana benthamiana plants induced a wilting phenotype. These findings suggest that, in wt plants PLDδ disrupt membranes in severe drought stress and, in the absence of the protein (PLDδ knock-out) might drought-prime the plants, making them more tolerant to severe drought stress. The results are discussed in relation to PLDδ role in guard cell signaling and drought tolerance. Fil: Distefano, Ayelen Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Valiñas, Matías Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Scuffi, Denise. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Lamattina, Lorenzo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Ten Have, Arjen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Garcia-Mata, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina Fil: Laxalt, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; Argentina

Cross-amplification of five Arabidopsis abiotic stress-responsive genes (AtPAP, ZFAN, Vn, LC4 and SNS) in Lepidium has been documented in plants raised out of seeds pre-treated with potassium nitrate (KNO 3) for assessment of enhanced drought stress tolerance. cDNA was synthesized from Lepidium plants pre-treated with KNO 3 (0.1% and 0.3%) and exposed to drought conditions (5% and 15% PEG) at seedling stage for 30 d. Transcript accumulation of all the five genes were found suppressed in set of seedlings, which were pre-treated with 0.1% KNO 3 and were exposed to 15% PEG for 30 d. The present study establishes that different pre-treatments may further enhance the survivability of Lepidium plants under conditions of drought stress to different degrees.

Substantial evidence indicates that drought stress promotes outbreaks of plant-eating (phytophagous) fungi and insects. Observations and experiments show that colonization success and prevalence of such fungi as root and stalk rots, stem cankers, and sometimes wilts and foliar diseases are much higher on water-stressed plants than on normal plants (Schoeneweiss 1986). The evidence associating insects and drought is more circumstantial, consisting largely of observations that outbreaks around the world of such insects as bark beetles and leaf feeders (see Table 1) are typically preceded by unusually warm, dry weather. There is also a consistent, positive correlation between insect outbreaks and dry, nutrient-poor sites (Mattson and Haack 1987).

Scots pine (Pinus sylvestris L.) provenances cover broad ecological amplitudes. In a greenhouse study, we investigated the impact of drought stress and rewetting on gas exchange for three provenances (Italy: Emilia Romagna; Spain: Alto Ebro; Germany: East-German lowlands) of 2-year old Scots pine seedlings. CO2, water vapour and isoprenoid exchange of stressed and control trees were quantified with a four-chamber dynamic-enclosure system in the controlled environment of a climate chamber. The three provenances showed distinct isoprenoid emission patterns and were classified into a non-Δ3-carene, with either high α-/β-pinene or β-myrcene fraction, and a Δ3-carene dominated type. Isoprenoid emission rates, net-photosynthesis and transpiration were reduced during summer drought stress and significantly recovered after rewetting. A seasonal increase of isoprenoid emission rates towards autumn was observed for all control groups. Compared with the German provenance, the Spanish and Italian provenances revealed higher isoprenoid emission rates and more plastic responses to drought stress and seasonal development, which points to a local adaptation to climate. As a result of drought, net carbon uptake and transpiration of trees was reduced, but recovered after rewetting. We conclude from our study that Scots pine isoprenoid emission is more variable than expected and sensitive to drought periods, likely impacting regional air chemistry. Thus, a provenance-specific emission assessment accounting for reduced emission during prolonged (summer) drought is recommend for setting up biogenic volatile organic compound emission inventories used in air quality models.

Dry root rot (DRR) disease is an emerging biotic stress threat to chickpea cultivation around the world. It is caused by a soil-borne fungal pathogen, Rhizoctonia bataticola. In the literature, comprehensive and detailed step-by-step protocols on disease assays are sparse. This article provides complete details on the steps involved in setting up a blotting paper technique for quickly screening genotypes for resistance to DRR. The blotting paper technique is easy and less expensive. Another method, based on the sick pot approach, is a mimic of natural infection and can be applied to study the interacting components-plant, pathogen, and environment-involved in the disease triangle. Moreover, in nature, DRR occurs mostly in rainfed chickpea cultivation areas, where soil moisture recedes as crop growth advances. Drought stress is known to predispose chickpea plants to DRR disease. Pathomorphological and molecular understanding of plant-pathogen interaction under drought stress can pave the way for the identification of elite DRR-resistant varieties from the chickpea germplasm pool. This article provides a stepwise methodology for the preparation of a sick pot and subsequent disease assay. Overall, the information presented herein will help researchers prepare R. bataticola fungal inoculum, maintain this pathogen, set up the blotting paper technique, prepare sick culture and sick pot, and assess pathogen infection in chickpea plants.

iv GENERAL INTRODUCTION 1 PAPER 1: EFFECTS OF DROUGHT STRESS AND DEFOLIATION ON PHYSIOLOGY, REGROWTH, AND SENESCENCE OF REMAINING LEAVES IN SOYBEAN 12 ABSTRACT 14 INTRODUCTION 15 MATERIALS AND METHODS 16 RESULTS 21 DISCUSSION 25 REFERENCES CITED 2714 INTRODUCTION 15 MATERIALS AND METHODS 16 RESULTS 21 DISCUSSION 25 REFERENCES CITED 27 PAPER 2: IMPACT OF DROUGHT STRESS AND DEFOLIATION ON YIELD OF SOYBEAN 39 ABSTRACT 4

The two-source energy balance model estimates canopy transpiration (Tr) and soil evaporation (E) traditionally from satellite partitions of remotely sensed land surface temperature (LST) and the Priestley-Taylor equation (TSEB-PT) at seasonal time with limited accuracy. The high spatial–temporal resolution spectral data collected by unmanned aerial vehicles (UAVs) provide valuable opportunity to estimate Tr and E precisely, improve the understanding of the seasonal and the diurnal cycle of evapotranspiration (ET), and timely detect agricultural drought. The UAV data vary in spatial resolution and the uncertainty imposed on the TSEB-PT outcome has thus far not being considered. To address these challenges and prospects, a new energy flux modelling framework based on TSEB-PT for high spatial resolution thermal and multispectral UAV data is proposed in this paper. Diurnal variations of LST in agricultural fields were recorded with a thermal infrared camera installed on an UAV during drought in 2018 and 2019. Observing potato as a test crop, LST, plant biophysical parameters derived from corresponding UAV multispectral data, and meteorological forcing variables were employed as input variables to TSEB-PT. All analyses were conducted at different pixelation of the UAV data to quantify the effect of spatial resolution on the performance. The 1 m spatial resolution produced the highest correlation between Tr modelled by TSEB-PT and measured by sap flow sensors (R2 = 0.80), which was comparable to the 0.06, 0.1, 0.5 and 2 m pixel sizes (R2 = 0.76–0.78) and markedly higher than the lower resolutions of 2 to 24 m (R2 = 0.30–0.72). Modelled Tr was highly and significantly correlated with measured leaf water potential (R2 = 0.81) and stomatal conductance (R2 = 0.74). The computed irrigation requirements (IRs) reflected the field irrigation treatments, ET and conventional irrigation practices in the area with high accuracy. It was also found that using a net primary production model with explicit representation of temperature influences made it possible to distinguish effects of drought vis-a-vis heat stress on crop productivity and water use efficiency. The results showed excellent model performance for retrieving Tr and ET dynamics under drought stress and proved that the proposed remote sensing based TSEB-PT framework at UAV scale is a promising tool for the investigation of plant drought stress and water demand; this is particularly relevant for local and regional irrigations scheduling. info:eu-repo/semantics/publishedVersion

Little is known about how soil properties control tree growth at its upper limit. This paper reviews the state of knowledge and discusses the results specifically related to ecozones, to the scale-dependent importance of single factors, and to new findings from a near-natural treeline ecotone in Rolwaling Himal, Nepal. This paper identifies gaps in literature and shows where new research is needed, both conceptual and geographical. The review shows that at a global scale and throughout diverse ecozones, growing season soil temperature is considered a key factor for tree growth. Soil temperatures differ greatly at a local scale, and are mainly determined by local climatic, edaphic, and topographic conditions. Our result of 7.6 ± 0.6°C for growing season mean soil temperature at treeline in Rolwaling is 1.2 K higher compared to the postulated 6.4 ± 0.7°C for alpine treelines. We suggest a broadening of the ±0.7°C error term to cover the wide range at a local scale. The role of major soil nutrients and soil moisture for treeline shift has been underestimated by far. In Rolwaling, significantly decreasing nutrient availability (N, K, Mg) in soils and foliage with elevation might explain why treeline shift and global warming are decoupled. Further, soil moisture deficits early in the year impede seedling and sapling establishment, which could be an important mechanism that controls treeline position. These findings question previous results which argue that alpine treelines are unaffected by soil nutrient availability and soil moisture. We assume that specific combinations of soil properties as well as single soil properties limit tree growth even below climatic treelines.

Short Retraction Notice The paper does not meet the standards of "Agricultural Sciences". This article has been retracted to straighten the academic record. In making this decision the Editorial Board follows COPE's Retraction Guidelines. The aim is to promote the circulation of scientific research by offering an ideal research publication platform with due consideration of internationally accepted standards on publication ethics. The Editorial Board would like to extend its sincere apologies for any inconvenience this retraction may have caused. Editor guiding this retraction: Prof. Daniele De Wrachien (EiC of AS). The full retraction notice in PDF is preceding the original paper which is marked "RETRACTED".

The paper is aimed at highlighting the physiological mechanisms associated with breeding of sweet potato towards drought tolerance. It describes important aspects including: the effects of drought stress, mechanisms of adaptation of crops to drought stress, drought stress on sweet potato, inheritance of drought tolerance, methods of screening and breeding of sweet potato for drought tolerance. The literature summarized in this paper may serve as important guideline in sweet potato breeding towards drought-tolerance. Key words: Breeding, drought-tolerance, genetics, physiology, sweet potato.

Drought stress exposure adversely affects plant growth and productivity. Various seed priming techniques are experimented to mitigate the adverse effect of drought stress on plant performance. It is a low-cost and sustainable technology that proved to be of immense potential to enhance drought tolerance and increase crop productivity. Drought episodes are followed by recovery through rain or irrigation and help the plants to recuperate from the damages caused by drought stress. The severity of drought-associated damages determines the recovery kinetics of plants. Under the recurrent cycle of drought events, recovery kinetics has immense importance in predicting the stress tolerance potential and survival status of a plant. Many processes like DNA damage repair, de-novo synthesis of nucleic acids and proteins, osmotic adjustment through the accumulation of osmolytes, the potential activity of antioxidant machinery occurring during seed priming play a significant role during recovery from drought stress. Alleviation of the severity of drought stress through the accumulation of osmolytes, the augmented activity of antioxidant machinery, improved photosynthetic performance, and the upregulated expression of stress-responsive genes attributed by seed priming will complement the recovery from drought stress. Although the beneficial effects of seed priming on drought tolerance are well explored, priming influenced recovery mechanism has not been well explored. There is a lacuna in the field of research related to the beneficial effects of seed priming for recovery from drought stress, and that is the focus of this paper.

Wheat (Triticum aestivum L.) is one of the major basic stable crops grown worldwide, however, it is sensitive to environmental stresses like drought. With climate change, drought stress is becoming an increasingly severe constraint on wheat production which affects the plant growth and development, physiological functions, grain formation, grain quality and ultimately the yield. Various responses including biochemical, physiological, morphological, and molecular adaptations are shown by plants to survive in the drought stress condition. Drought escape, avoidance and tolerance are important coping mechanisms of wheat plant under drought environment. Several mechanisms such as accumulation of ABA, osmotic adjustment, and induction of dehydrins may confer drought tolerance by maintaining the high tissue water potential. As the root structure and root biomass define the pattern of water extraction from the soil, enhanced root and suppressed shoot growth resulting in higher root: shoot ratio facilitated plants to drought tolerance. The development of drought tolerance varieties becomes an important due to the uneven distribution of rainfall and water shortage. Some growth stage-specific physio-morphological traits are fundamental targets to breed drought-tolerant wheat varieties. Mutation breeding, molecular breeding, genome engineering techniques including gene pyramiding, gene stacking, and transgenics are employed to breed wheat for tolerance to abiotic stresses including drought. Omics decode the entire genome to have better understanding of plant molecular responses that will provide precise strategies for crop improvement. This paper discusses the wheat plant’s responses to drought stress, their defense mechanisms and modern techniques for the development of drought tolerant wheat varieties.

Drought is one the most common adverse environmental problem is increasing as a result of increasing population of world and intensive use of natural resources. Drought stress has major constraints to agricultural productivity worldwide, particularly in warm, arid and semi-arid areas. It adversely affects plants Morphological, Physiological and Biochemical processes and prolonged drought stress limits plant growth and productivity. The effect of drought stress at a whole plant level results non-normal physiological process that impact one or a combination of biological and environmental factors. That is why this review paper is mainly focused on recent information about the influence of water stress on plants, as well as its mechanisms of adaptation. It is shown that plants have evolved physiological and biochemical adaptations to cope with water stress. Plant used molecular mechanism to increase tolerance against drought are discussed. The literature analysed in this review shows an understanding of how these systems are regulated and upgrade the effect of drought stress on plants mechanism. The provided information needed to improve plants tolerance against drought stress by using biotechnological tools.