Acute Drought Stress Research Articles

Physiological and biochemical changes of Picea abies (L.) during acute drought stress and their correlation with susceptibility to Ips typographus (L.) and I. duplicatus (Sahlberg)

IntroductionIn recent years, Norway spruce (Picea abies L.) forests in Central Europe have faced escalating threats from bark beetles, primarily Ips typographus (L.), and other species, such as I. duplicatus (Sahlberg). Outbreaks are partially attributed to weakened tree defense resulting from drought periods induced by climate change. This study examines Norway spruce’s physiological and metabolic reactions to acute drought stress during the growing season and evaluates its susceptibility to I. typographus and I. duplicatus.MethodologyIn order to induce drought stress, mature Norway spruces had their roots covered with a roof in April 2021, depriving them of water. Control trees were left with free access to natural rainwater. Over 5 months of the growing season, soil water potential, bark temperature, tree trunk circumference, and sap flow were monitored. Roofed trees and controls were sampled in July, August, and September and analyzed for non-structural carbohydrates and the two classes of defensive compounds, phenolics and terpenes. Furthermore, two different bioassays in tubes and boxes were performed using adult I. typographus and I. duplicatus beetles to assess host choice and acceptance.ResultsRoofed trees exhibited signs of stress as early as July, resulting in decreased tree trunk and a consequent increase in non-structural carbohydrate content. Defensive metabolites remained largely unaffected except for an increase in diterpenes in September. In bioassays, I. typographus preferred boring into the bark of roofed trees in August in tubes and in September in boxes. This increased tree acceptance correlated with increased levels of soluble carbohydrates in the phloem. I. typographus and I. duplicatus beetles showed higher mobility in boxes in August and September on roofed trees but not in July, even though bark surface temperatures were elevated in roof-covered trees during all three bioassay periods.ConclusionThe study revealed rapid physiological responses of trees to acute drought stress, although not many changes were observed in defense traits. Despite the absence of natural bark beetle attacks, drought trees were more accepted by I. typographus than naturally watered trees. This response may indicate the beetles’ preference for trees with phloem of higher nutritional quality induced by the acute drought stress conditions.

Comparative analysis of physiology-anatomy and transcriptome-metabolome involving acute drought stress response of root between two distinct peanut cultivars at seedling stage

Drought is a major abiotic stress that restricts plant development, especially at seedling stage, which stimulates reduction of shoot, root absorb ability, and biomass accumulation of plant. Peanut, as a plant with resilience to drought stress, can still cause serious condensed shoot and impaired flower bud differentiation under drought conditions resulting in yield loss. In order to find those drought responses of peanut at seedling stage, two distinct cultivars with different drought resistance (HY22 and FH18) were screened previously and used to investigate the difference of drought response by deciphering the changes of morphology, physiology-anatomy, and transcriptome. The results showed that drought stress decreased root morphological indices both in two cultivars, but HY22 showed higher root vigor and lateral roots. Furthermore, HY22 enhanced the activity of antioxidant enzymes such as POD, SOD to reduce lipid peroxidation and H2O2 concentration, in which stable root anatomical structure and microstructure were kept. By contrast, SOD and POD decreased, and MDA and H2O2 increased, in which gave impair anatomical structure and microstructure in FH18. Using high-throughput RNA sequencing, we developed a spatiotemporal transcriptome atlas of HY22 and FH18 at seedling stage. A total of 34,303 and 34,689 genes for HY22 and FH18 were found to be expressed under the drought stress, respectively. Global comparisons of gene expression showed more differentially expressed genes (DEGs) were detected in HY22. Moreover, co-expression analysis of overlapped DEGs between HY22 and FH18 revealed that the up-regulated genes of HY22 mainly related to hormone-mediated signaling pathway, response to abscisic acid and flavonoid biosynthetic process. According to the findings, the genotype HY22 was more tolerant to drought stress than FH18 by improving SOD and POD enzyme activities, membrane stability, root vigor, and maintaining fine cell microstructure and relatively up-regulated express levels of genes and metabolin revolving in ABA transduction signal, terpenoids skeleton and flavonoid biosynthesis. The results of the current study provide theoretical reference for elaborating drought resistance mechanism more accurately and precisely.

Type and duration of water stress influence host selection and colonization by exotic ambrosia beetles (Coleoptera: Curculionidae).

Fungus-farming ambrosia beetles in the tribe Xyleborini tunnel into plants and trees to establish chambers for cultivating their nutritional fungal mutualists and rearing offspring. Some xyleborine ambrosia beetles preferentially infest and perform better in living but weakened trees. Flood stress predisposes horticultural tree crops to infestation, but the impact of drought stress has not been well studied. Our objectives were to compare the effects of flood stress vs. drought stress on host selection and colonization by xyleborine ambrosia beetles and to assess the duration of flooding. Container-grown Cornus florida L. trees were flood stressed using a pot-in-pot system to submerge the roots in water while drought-stressed conditions were imposed by withholding irrigation and precipitation. When experimental trees were held under field conditions for 14 days, 7.5× more ambrosia beetles landed on stems of the flood-stressed than on the drought-stressed trees. During two additional experiments over 14 and 22 days, ambrosia beetles tunneled into the flood-stressed trees but not the drought-stressed or standard irrigation trees. By simultaneously deploying trees that were flood stressed for varying lengths of time, it was found that more tunnel entrances, and xyleborine adults and offspring were recovered from trees that were flooded for 1-16 days and 7-22 days than from trees that were flooded for 14-29 days and 28-43 days. These results indicate that acute and severe drought stress does not predispose C. florida to infestation, but flood stress and the duration of flooding influence ambrosia beetle host selection and colonization. Understanding the role of host quality on ambrosia beetle preference behavior will assist with predicting the risk of infestation of these opportunistic insects in horticultural tree crops.

Detection of susceptible Norway spruce to bark beetle attack using PlanetScope multispectral imagery

Climate change-related acute or long-term drought stress can weaken forest ecosystems and result in widespread bark beetle infestations. Eurasian spruce bark beetle (Ips typographus L.) infestations have been occurring in Norway spruce [Picea abies (L.) Karst.]-dominated forests in central Europe including the Czechia. These infestations appear regularly, especially in homogeneous spruce stands, and the impact varies with the climate-induced water stress conditions. The removal of infected trees before the beetles leave the bark is an important step in forest pest management. Early identification of susceptible trees to infestations is also very important but quite challenging since stressed tree-tops show no sign of discolouration in the visible spectrum. We investigated if individual spectral bandwidths or developed spectral vegetation indices (SVIs), can be used to differentiate non-attacked trees, assumed to be healthy, from trees susceptible to attacks in the later stages of a growing season. And, how the temporal-scale patterns of individual bands and developed SVIs of susceptible trees to attacks, driven by changes in spectral characteristics of trees, behave differently than those patterns observed for healthy trees. The multispectral imagery from the PlanetScope satellite coupled with field data were used to statistically test the competency of the individual band and/or developed SVIs to differentiate two designated classes of healthy and susceptible trees. We found significant differences between SVIs of the susceptible and healthy spruce forests using the Enhanced Vegetation Index (EVI) and Visible Atmospherically Resistant Index (VARI). The accuracy for both indices ranged from 0.7 to 0.78; the highest among all examined indices. The results indicated that the spectral differences between the healthy and susceptible trees were present at the beginning of the growing season before the attacks. The existing spectral differences, likely caused by water-stress stimuli such as droughts, may be a key to detecting forests susceptible to early infestations. Our introduced methodology can also be applied in future research, using new generations of the PlanetScope imagery, to assess forests susceptibility to bark beetle infestations early in the growing season.

Effects of soil water and nitrogen on drought resilience, growth, yield, and grain quality of a spring wheat

Drought imposes a significant challenge for crop production. However, little is known about the impact of drought priming and nitrogen (N) application and their interactive effects on drought resilience, yield, and grain quality in wheat. Spring wheat (cv. Stettler) was grown in plastic pots (25 cm diameter) with high, moderate, and low soil water levels and received N (added N) or without N (no N added), and subjected to acute drought for 10 days, then rewatering at the tillering stage. Canopy temperature, maximum efficiency of photosystem II, and normalized difference vegetation index were measured at 3-day intervals during drought-recovery periods to quantify drought resistance and resilience. Above-ground dry matter, straw dry matter, seed dry matter, harvest index, and grain N, phosphorus (P), and zinc (Zn) concentrations were determined. Both moderate- and low-water-grown plants had higher drought resistance than high-water-grown plants. The addition of N alleviated acute drought stress in high- and moderate-water-grown plants but exacerbated drought stress in low-water-grown plants. Both high and moderate water resulted in higher grain yields, but had a lower harvest index than low water. The highest and lowest grain N were observed in the low- and high-water-grown plants, respectively. The addition of N increased N and N:P in grains but decreased grain Zn:N. This study showed that moderate drought priming along with N application can improve drought resistance, yield, and grain quality. The results also indicated that canopy thermal imaging is a useful tool for high-throughput quantification of the drought resistance of wheat.

Drought-induced decoupling between carbon uptake and tree growth impacts forest carbon turnover time

The ability of forests to withstand, and recover from, acute drought stress is a critical uncertainty regarding the impacts of climate change on the terrestrial carbon (C) cycle, but it is unclear how drought responses scale from individual trees to whole forests. Here, we assembled a dataset of tree-ring chronologies co-located within the footprint of eddy covariance towers across North America and Europe, with the aim of quantifying the sensitivity of tree radial growth versus gross primary productivity (GPP) during and following drought. We found that drought induced a large decoupling across C cycle processes, whereby GPP was relatively resistant to water stress despite large reductions in tree-ring widths. This decoupling also occurred in the year following drought (i.e., a ‘drought legacy effect’), and was similar in magnitude in response to both summer and winter droughts. By modeling whole-forest C turnover time, we show that a radial growth-GPP decoupling has important ramifications for the forest C cycle, especially if the C not used to support radial growth is instead allocated towards pools with short residence times. Our results demonstrate that quantifications of drought impacts that rely solely on C uptake are missing this fundamental pathway through which drought alters the forest C cycle and the resulting feedbacks to the climate system.

Inferring the genetic responses to acute drought stress across an ecological gradient

BackgroundHow do xerophytic species thrive in environments that experience extreme annual drought? Although critical to the survival of many species, the genetic responses to drought stress in many non-model organisms has yet to be explored. We investigated this question in Mentzelia section Bartonia (Loasaceae), which occurs throughout western North America, including arid lands. To better understand the genetic responses to drought stress among species that occur in different habitats, the gene expression levels of three species from Mentzelia were compared across a precipitation gradient. Two de novo reference transcriptomes were generated and annotated. Leaf and root tissues were collected from control and drought shocked plants and compared to one another for differential expression. A target-gene approach was also implemented to better understand how drought-related genes from model and crop species function in non-model systems.ResultsWhen comparing the drought-shock treatment plants to their respective control plants, we identified 165 differentially expressed clusters across all three species. Differentially expressed genes including those associated with water movement, photosynthesis, and delayed senescence. The transcriptome profiling approach was coupled with a target genes approach that measured expression of 90 genes associated with drought tolerance in model organisms. Comparing differentially expressed genes with a ≥ 2 log-fold value between species and tissue types showed significant differences in drought response. In pairwise comparisons, species that occurred in drier environments differentially expressed greater genes in leaves when drought shocked than those from wetter environments, but expression in the roots mostly produced opposite results.ConclusionsArid-adapted species mount greater genetic responses compared to the mesophytic species, which has likely evolved in response to consistent annual drought exposure across generations. Drought responses also depended on organ type. Xerophytes, for example, mounted a larger response in leaves to downregulate photosynthesis and senescence, while mobilizing carbon and regulating water in the roots. The complexity of drought responses in Mentzelia suggest that whole organism responses need to be considered when studying drought and, in particular, the physiological mechanisms in which plants regulate water, carbon, cell death, metabolism, and secondary metabolites.

Northernmost European spruce bark beetle Ips typographus outbreak: Modelling tree mortality using remote sensing and climate data

Acute or chronic drought stress caused by climate change can contribute to the weakening of forest ecosystems and lead to extensive bark beetle infestations. Siberian spruce (Picea obovata Ledeb.) forests of the Dvinsko-Pinegskiy, a natural reserve in the Arkhangelsk region, Russia, have been subject to unprecedented tree cover loss caused by the Eurasian spruce bark beetle (Ips typographus L.) in the last two decades. This is the first recorded case of such an extensive outbreak of Ips typographus occurring at higher latitudes. We used remote sensing and climate data to model and compute annual tree-loss change due to natural factors, with a focus on bark beetle outbreaks, over a 14-year period (2001–2014). Usinglinear regression models, we found a combination of average annual temperature and precipitation, temperature and precipitation in June, to be the most important drivers of annual tree-loss.

Transcriptome-Based Identification and Functional Characterization of NAC Transcription Factors Responsive to Drought Stress in Capsicum annuum L.

Capsicum annuum L. is one of the most cultivated Solanaceae species, and in the open field, water limitation leading to drought stress affects its fruit quality, fruit setting, fruit size and ultimately yield. We identified stage-specific and a common core set of differentially expressed genes, following RNA-seq transcriptome analyses of a breeding line subjected to acute drought stress followed by recovery (rewatering), at three stages of plant development. Among them, two NAC transcription factor (TF) genes, i.e., CaNAC072 and CaNAC104, were always upregulated after drought stress and downregulated after recovery. The two TF proteins were observed to be localized in the nucleus following their transient expression in Nicotiana benthamiana leaves. The expression of the two NACs was also induced by NaCl, polyethylene glycol (PEG) and abscisic acid (ABA) treatments, suggesting that CaNAC072 is an early, while CaNAC104 is a late abiotic stress-responsive gene. Virus-induced gene silencing (VIGS) of CaNAC104 did not affect the pepper plantlet’s tolerance to drought stress, while VIGS of CaNAC072 increased drought tolerance. Heterologous expression of CaNAC072 in Arabidopsis thaliana as well as in plants mutated for its homolog ANAC072 did not increase drought stress tolerance. This highlights a different role of the two NAC homologs in the two species. Here, we discuss the complex role of NACs as transcriptional switches in the response to drought stress in bell pepper.

The influence of acute water stresses on the biochemical composition of bell pepper (Capsicum annuum L.) berries.

Crops are exposed to recurrent and acute drought stress episodes during their vegetative and reproductive cycles, and these episodes are increasingly frequent due to ongoing climate change. Sweet pepper (Capsicum annuum), alias bell pepper, is one of the most widely cultivated vegetables and is grown in open fields worldwide. Here we assessed the effect of acute water stress, applied to a breeding line of sweet pepper at three stages of plant development: five true-leaves (Stage 1), production of the third flower (Stage 2) and setting of the first fruit (Stage 3), on the production and biochemical composition of its ripe fruits. The water stress at Stages 1 and 2 induced a delay in fruit ripening, while at Stage 3 caused a drop in production. The biochemical composition of ripe fruits was assessed by quantifying their content in vitamin C, sugars, organic acids, flavonoids as well as 190 volatile organic compounds, mainly belonging to the chemical classes of hydrocarbons, alcohols, ketones, esters, terpenes, aldehydes and ethers. Our results highlight that, at different stages of plant development, acute water stresses modulate differently the accumulation of bioactive compounds in fruits, which play a key role in setting the redox-status and osmotic adjustment of the plant. This was also the case for volatile compounds since, within each chemical class, different compounds varied their content in ripe fruits. On the whole, our results demonstrate that water stresses potentially affect the organoleptic and sensory qualities of bell pepper fruits depending on when they occur. © 2021 Society of Chemical Industry.

Ecological divergence of wild strawberry DNA methylation patterns at distinct spatial scales.

Epigenetic change is considered relatively unstable and short-lived, raising questions of its contribution to long-term adaptive potential. However, epigenetic modifications can accumulate in the presence of environmental stress, resulting in beneficial epigenetic memories where environments are challenging. Diverging epigenetic memories have been observed across large spatial scales, and can persist through multiple generations. It is unknown, however, to what extent epigenetic variation contributes to fine-scale population structure and evolution. We compared DNA methylation patterns between a steep, altitudinal gradient (<2km) and a wide spatial gradient (>500km) using whole genome bisulphite sequencing data from 30 Fragaria vesca plants germinated and grown in controlled conditions. To assess the stability of spatial epigenetic variation in the presence of an environmental stressor, we applied acute drought stress to part of the plants and quantified drought-induced changes in DNA methylation signatures. We find that epigenetic memories and genomic islands of epigenetic divergence arise even at fine spatial scale, and that distinct spatial scales are featured by distinct epigenetic patterns. For example, demethylation of transposable elements consistently occurred at the large but not the fine spatial scale, while methylation differentiation for most biological processes were shared between spatial scales. Acute drought stress did not result in significant epigenetic differentiation. Our results indicate that population history, rather than short-term environmental stress, plays a dominant role in shaping epigenetic signatures. Specifically, repeated historical stress levels associated with heterogeneous environmental conditions may be required for acquiring a stable epigenetic memory and for coping with future environmental change.

Rapid and surprising dieback of Utah juniper in the southwestern USA due to acute drought stress

For nearly two decades, the American Southwest has been in the grips of a long-term ‘megadrought’, punctuated by a number of short and severe ‘global change type droughts’ (i.e., negative precipitation anomalies co-occurring with high temperature). These events have caused widespread mortality of the drought-sensitive piñon pine (Pinus edulis) while co-dominant Juniperus spp. have historically been much more drought tolerant and thus have rarely died. However, a severe drought occurred in 2018 that rapidly (<1 year) caused canopy dieback of Juniperus osteosperma across a vast area of southeastern Utah. In order to uncover the etiology behind this surprising dieback event, we set up a series of survey plots that captured gradients in microclimate, topography, and dieback severity. We also quantified xylem hydraulic damage and assessed the presence of various biotic agents in declining junipers to identify the primary causes of this dieback. We observed that juniper canopy dieback was most severe (>60% canopy dieback) at hot, dry, low elevation sites, and was associated with drought-induced hydraulic damage. There was no evidence that biotic agents could be the primary drivers of this dieback, implicating the acute effects of drought as the main causal agent. The speed and scale of this drought-induced juniper dieback seems to be historically unprecedented in the region and foreshadows an uncertain future for piñon-juniper woodlands as the region continues to get warmer and drier.

Acute Drought Is an Important Driver of Bark Beetle Infestation in Austrian Norway Spruce Stands

Infestations of Norway spruce by the Eurasian spruce bark beetle Ips typographus have recently caused peaks in salvaged timber in Central European forests. Apart from extensive breeding material due to abiotic disturbance, increased spring and summer temperatures as well as precipitation deficits are presumably key drivers of bark beetle population dynamics. In this study, we investigated the influence of effective temperature sums, chronic and acute drought stress, and stand characteristics for explaining salvage logging due to bark beetle attack in Norway spruce stands of Austrian Federal Forests. We retrospectively simulated temperature and transpiration deficit as drought proxy by use of the monitoring tool PHENIPS-TDEF, a well-proven bark beetle phenology model, combined with an additional hydrological module developed for simulating transpiration deficits (TDEF) in forest stands. Overall, we found that bark beetle infestation occurred more frequently in stands with high share of Norway spruce, increased stand age and stand density. The probability of ongoing attacks was significantly higher in stands subject to salvage logging in the previous year. Chronically dry forest stands described in the forest inventory database as growing on shallow, xeric, and low moisture soil conditions, were significantly less prone to bark beetle attack across all forest enterprises. However, acute drought indicated by stand transpiration deficits was a significant predictor of bark beetle attacks, especially in stands geographically located in warmer and drier areas of the country. Although importance of TDEF parameters differed with geographic location and observation period, the clear increase in attacks across all forest stands in 2015 was principally linked to previous year’s and actual summer transpiration deficits. We conclude from our results that in the absence of severe abiotic disturbance a combination of ample host availability, favorable temperature conditions for bark beetle development, and acute disposition of trees to attack caused by drought stress can intensify population growth and very likely lead to bark beetle mass outbreaks.

The Role of the Plant Antioxidant System in Drought Tolerance.

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

Grassland plants show no relationship between leaf drought tolerance and soil moisture affinity, but rapidly adjust to changes in soil moisture

Abstract Assessing drought tolerance and the ability of plants to adjust to changes in available water resources is crucial for understanding current and future distributions of plant species. While turgor loss point (πtlp) has been recognized as a direct determinant of drought tolerance in woody plants, information on it for grassland species is largely missing. We first validated a rapid method to estimate πtlp for grassland species, using osmometry measurements (πtlp‐osm) of osmotic potential at full hydration (πo‐osm), originally proposed for woody species. We confirmed that πo‐osm was tightly positively related to πtlp measured by the classic pressure–volume curve (πtlp‐pv). Cell wall elasticity was not important in the maintenance of turgor and neither specific leaf area nor leaf dry matter content influenced πtlp. We then studied the relationship between πtlp‐osm measured under controlled conditions and species’ soil moisture affinity (Ellenberg indicator values) in 40 diverse grassland species from the full range of soil moisture conditions found in temperate grasslands. On a subset of 12 species, we studied the adjustment in πtlp‐osm to drought stress and recovery from drought. We hypothesized that dry grassland species are better adapted to drier conditions by having comparatively higher leaf drought tolerance (more negative πtlp) and a better ability to adjust to acute drought stress. We found that πtlp‐osm was unrelated to species’ soil moisture affinity. However, all species developed higher leaf drought tolerance by decreasing πtlp‐osm after seven weeks of drought stress. After only one week of recovery, all species reduced the leaf drought tolerance back to the πtlp‐osm level comparable with non‐stressed plants. Our results considerably extend the relationship between πo‐osm and πtlp, originally defined for woody species, and thus propose a yet unexploited direct method for assessing leaf drought tolerance via turgor loss point in herbaceous species. However, the lack of relationship between πtlp and soil moisture affinity suggests that, unlike in woody plants, leaf‐level drought tolerance in grassland plants does not fully translate into whole‐plant drought resistance, suggesting an importance of other drought resistance strategies. A plain language summary is available for this article.

Transcriptomic responses in Neolitsea sericea leaves under acute drought stress

Neolitsea sericea is acclimated to arid islands, but few studies have examined its responses to water stress. To look into the defending responses that assist N. sericea seedlings to survive drought, physiological and transcriptomic analysis of leaves was conducted after drought was induced. Over 17,768,244 reads for each sample were generated, totalling over 4400 million base pairs (bp). Among 129,239 unigenes that were assembly yielded with an average length of 816 bp, 51,137 of them (39.6%) were annotated successfully. Under severe drought, physiological inhibition was strengthened and abscisic acid content was significantly upregulated. The responses were strongly accompanied by transcriptional regulation of genes participating in stress perception, protective signalling, hormone metabolism, transcription factors, abiotic stress, transport, and degradation. In total, 61, 65, and 67 differentially expressed genes were identified after 12, 24, and 72 h exposure to severe drought stress, respectively. Gene Ontology and MapMan functional enrichment analysis revealed that the most upregulated genes were involved in protein transport, the regulation of transcription, and miscellaneous enzyme families. In addition, genes that encode glycosyl transferase and UDP-glycosyltransferases may modulate the drought-stress responses of N. sericea. Multiple hormones were active in N. sericea leaves during drought stress, including those associated with auxins, abscisic acid, brassinosteroid, and cytokinins. Transcription factors, including AtbHLH112, AtCOL4, AtZFP3, AtCIR1, and AtCCA1, may participate in ABA signal transduction in drought-treated N. sericea. The present study elucidates how N. sericea make transcriptomic responses to drought stress, helping to reveal the molecular mechanisms connected to drought adaptation.

Physiological and structural adjustments of two ecotypes of Platanus orientalis L. from different habitats in response to drought and re-watering.

Platanus orientalis covers a very fragmented area in Europe and, at the edge of its natural distribution, is considered a relic endangered species near extinction. In our study, it was hypothesized that individuals from the edge of the habitat, with stronger climate constrains (drier and warmer environment, Italy, IT ecotype), developed different mechanisms of adaptation than those growing under optimal conditions at the center of the habitat (more humid and colder environment, Bulgaria, BG ecotype). Indeed, the two P. orientalis ecotypes displayed physiological, structural and functional differences already under control (unstressed) conditions. Adaptation to a dry environment stimulated constitutive isoprene emission, determined active stomatal behavior, and modified chloroplast ultrastructure, ultimately allowing more effective use of absorbed light energy for photochemistry. When exposed to short-term acute drought stress, IT plants showed active stomatal control that enhanced instantaneous water use efficiency, and stimulation of isoprene emission that sustained photochemistry and reduced oxidative damages to membranes, as compared to BG plants. None of the P. orientalis ecotypes recovered completely from drought stress after re-watering, confirming the sensitivity of this mesophyte to drought. Nevertheless, the IT ecotype showed less damage and better stability at the level of chloroplast membrane parameters when compared to the BG ecotype, which we interpret as possible adaptation to hostile environments and improved capacity to cope with future, likely more recurrent, drought stress.

Depicting how Eucalyptus globulus survives drought: involvement of redox and DNA methylation events.

Eucalyptus globulus Labill. is widely cultivated and used by industry but its productivity is currently restricted by drought events, so research focussing on supporting programs to breed adapted germplasm is needed. In the present work we monitored severity of acute drought stress (7 and 11 days after water withholding) and relief (2h and 3 days after rewatering) by quantifying several biochemical markers of oxidative stress and DNA methylation patterns in leaves. Water withholding imposed a mild oxidative stress as estimated by redox shifts in the major antioxidant pools and increased lipid peroxidation. At the DNA level, global 5-methylcytosine distribution increased over the dehydration period especially in vascular tissue as estimated by immunolocalisation. Using methylation-sensitive RAPD analysis, which discriminates methylation changes occurring in specific DNA sequences, we found a high number of specific demethylation events also taking place. Immunolocalisation indicated a rapid reduction in global DNA methylation 2h after rehydration; however, a large number of de novo methylation events were still detected by methylation-sensitive RAPD. These events were associated with decreased lipid peroxidation and high cellular GSH pools relative to unstressed plants. Our results indicate the parallel induction of redox and complex DNA methylation changes occurring during stress imposition and relief.

Environmentally dependent host–pathogen and vector–pathogen interactions in the Barley yellow dwarf virus pathosystem

Summary Understanding environmentally dependent variation in interspecific interactions is needed for evaluating how agroecosystems respond to abiotic stressors, including climate change. Both biotic and abiotic conditions shape crop responses to stress events, but interactions between environmental conditions and insect borne plant pathogens remain poorly understood. We tested the hypothesis that drought stress, as applied by experimental water deprivation, drives conditional outcomes in host–pathogen and host–vector interactions using a cereal–aphid–virus association and greenhouse experiments. Under conditions of ample water supply, infection of wheat plants with Barley yellow dwarf virus (BYDV) resulted in reduced above‐ground growth, seed set, seed yields and seed germination compared with plants exposed only to non‐infected (non‐viruliferous) aphids or control plants not subjected to aphid infestation. However, when water was chronically limiting, infection with Barley yellow dwarf virus did not significantly affect plant performance. When wheat was subjected to acute drought stress, plants infected with Barley yellow dwarf virus surpassed both control plants and plants exposed to non‐infected aphids in all measured performance traits. Feeding experiments with aphid vectors (Rhopalosiphum padi) and subsequent life table analysis revealed that aphid fecundity improved by 47% when feeding on Barley yellow dwarf virus‐infected plants when water inputs were chronically low. However, when plants received ample water, aphid fecundity was enhanced by only 23% from feeding on BYDV‐infected plants. Synthesis and applications. Collectively, our experiments suggest that wheat– Barley yellow dwarf virus interactions shift along gradients of water stress severity and duration. When Barley yellow dwarf virus infection preceded water deprivation, plant performance was not reduced from virus infection, and infected plants recovered from severe stress events more readily than non‐infected plants. However, vector–pathogen mutualism resulting in enhanced reproduction of aphids on virus‐infected plants is likely to amplify direct plant injury from herbivory in the field. Our findings indicate that during periods of drought, management of Barley yellow dwarf virus infection may not be needed and infection could benefit wheat under conditions of acute water stress.

Accelerated Growth Rate and Increased Drought Stress Resilience of the Model Grass Brachypodium distachyon Colonized by Bacillus subtilis B26.

Plant growth-promoting bacteria (PGB) induce positive effects in plants, for instance, increased growth and reduced abiotic stresses susceptibility. The mechanisms by which these bacteria impact the host plant are numerous, diverse and often specific. Here, we studied the agronomical, molecular and biochemical effects of the endophytic PGB Bacillus subtilis B26 on the full life cycle of Brachypodium distachyon Bd21, an established model species for functional genomics in cereal crops and temperate grasses. Inoculation of Brachypodium with B. subtilis strain B26 increased root and shoot weights, accelerated growth rate and seed yield as compared to control plants. B. subtilis strain B26 efficiently colonized the plant and was recovered from roots, stems and blades as well as seeds of Brachypodium, indicating that the bacterium is able to migrate, spread systemically inside the plant, establish itself in the aerial plant tissues and organs, and is vertically transmitted to seeds. The presence of B. subtilis strain B26 in the seed led to systemic colonization of the next generation of Brachypodium plants. Inoculated Brachypodium seedlings and mature plants exposed to acute and chronic drought stress minimized the phenotypic effect of drought compared to plants not harbouring the bacterium. Protection from the inhibitory effects of drought by the bacterium was linked to upregulation of the drought-response genes, DREB2B-like, DHN3-like and LEA-14-A-like and modulation of the DNA methylation genes, MET1B-like, CMT3-like and DRM2-like, that regulate the process. Additionally, total soluble sugars and starch contents increased in stressed inoculated plants, a biochemical indication of drought tolerance. In conclusion, we show a single inoculation of Brachypodium with a PGB affected the whole growth cycle of the plant, accelerating its growth rates, shortening its vegetative period, and alleviating drought stress effects. These effects are relevant to grasses and cereal crops.