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PubMed1985

Mean geocarposphere temperatures that induce preharvest aflatoxin contamination of peanuts under drought stress.

Apparently undamaged peanuts grown under environmental stress in the form of drought and heat become contaminated with Aspergillus flavus and aflatoxin in the soil prior to harvest. The upper mean temperature limit for aflatoxin contamination in undamaged peanut kernels grown under drought stress the latter 4-6 weeks of the growing season was between 29.6-31.3 degrees C. The lower limit was between 25.7-26.3 degrees C. That is, peanuts grown under drought stress with a mean geocarposphere temperature of 29.6 degrees C were highly contaminated while those at 31.3 degrees C were not contaminated. Likewise, those grown under drought stress with a mean geocarposphere temperature of 25.7 degrees C were not contaminated while those subjected to a mean geocarposphere temperature of 26.0 degrees C resulted in some categories becoming contaminated. Increasing the mean temperature up to 29.6 degrees C caused increasing amounts of contamination.

Aflatoxins↗

PubMed2005

QTLs for drought escape and tolerance identified in a set of random introgression lines of rice.

A large set of 254 introgression lines in an elite indica genetic background were evaluated for grain yield (GY) and related traits under the irrigated (control) and drought (stress) conditions in two consecutive years for genetic dissection of adaptive strategies of rice to water stress. A total of 36 quantitative trait loci (QTLs) affecting heading date (HD), plant height (PH), GY and yield components were identified and most QTLs showed pronounced differential expression either qualitatively or quantitatively in response to drought. These QTLs could be grouped into three major types based on their behaviors under control and stress conditions. Type I included 12 QTLs that expressed under both the stress and non-stress conditions. Type II comprised 17 QTLs that expressed under irrigation but not under stress. Type III included seven QTLs that were apparently induced by stress. The observation that the Lemont (japonica) alleles at all HD QTLs except QHd5 resulted in early heading under stress appeared to be responsible for the putative adaptation of Lemont to drought by escaping, whereas the Teqing (indica) alleles at most PH/GY QTLs were consistently associated with increased yield potential and trait stability and thus contributed to DT. Our result that most DT QTLs were non-allelic with QTLs for drought escaping suggests that the two adaptive strategies in the parental lines are under possible negative regulation of two largely non-overlapping genetic systems.

Adaptation, Biological↗

PubMed2006

A branched-chain amino acid aminotransferase gene isolated from Hordeum vulgare is differentially regulated by drought stress.

Differential display was used to isolate cDNA clones showing differential expression in response to ABA, drought and cold in barley seedling shoots. One drought-regulated cDNA clone (DD12) was further analyzed and found to encode a branched-chain amino acid aminotransferase (HvBCAT-1). A genomic clone was isolated by probing the Morex BAC library with the cDNA clone DD12 and the structure of Hvbcat-1 was elucidated. The coding region is interrupted by six introns and contains a predicted mitochondrial transit peptide. Hvbcat1 was mapped to chromosome 4H. A comparison was made to rice and Arabidopsis genes to identify conserved structural patterns. Complementation of a yeast (Saccharomyces cerevisiae) double knockout strain revealed that HvBCAT-1 can function as the mitochondrial (catabolic) BCATs in vivo. Transcript levels of Hvbcat-1, increased in response to drought stress. As the first enzyme in the branched-chain amino acid (BCAA) catabolic pathway, HvBCAT-1 might have a role in the degradation of BCAA. Degradation of BCAA could serve as a detoxification mechanism that maintains the pool of free branched-chain amino acids at low and non toxic levels, under drought stress conditions.

Abscisic Acid↗

PubMed2006

Identification of a gene from the arbuscular mycorrhizal fungus Glomus intraradices encoding for a 14-3-3 protein that is up-regulated by drought stress during the AM symbiosis.

In the present study, a 14-3-3 protein-encoding gene from Glomus intraradices has been identified after differential hybridization of a cDNA library constructed from the fungus growing in vitro and subjected to drought stress by addition of 25% PEG 6000. Subsequently, we have studied its expression pattern under drought stress in vitro and also when forming natural symbioses with different host plants. The results obtained suggest that Gi14-3-3 gene may be involved in the protection that the arbuscular mycorrhizal (AM) symbiosis confers to the host plant against drought stress. Our findings provide new evidences that the contribution of AM fungi to the enhanced drought tolerance of the host plant can be mediated by a group of proteins (the 14-3-3) that regulate both signaling pathways and also effector proteins involved in the final plant responses.

14-3-3 Proteins↗

PubMed2006

Microbial availability and size fractionation of dissolved organic carbon after drought in an intermittent stream: biogeochemical link across the stream-riparian interface.

The evolution of dissolved organic carbon (DOC) molecular-weight fractions, DOC biodegradability (BDOC), DOC origin [fluorescence index (FI)], and enzyme activities between the stream waters (main and ephemeral channel) and ground waters (riparian and hillslope) were analyzed during the transition from drought to precipitation in a forested Mediterranean stream. After the first rains, DOC content in stream water reached its maximum value (10-18 mg L(-1)), being explained by the leaching of deciduous leaves accumulated on the stream bed during drought. During this period, the largest molecules (>10 kDa), were the most biodegradable, as indicated by high BDOC values measured during storm events and high enzymatic activities (especially for leucine-aminopeptidase). DOC >100 kDa was strongly immobilized (78%) at the stream-riparian interface, whereas the smallest molecules (<1 kDa) were highly mobile and accumulated in ground waters, indicating their greater recalcitrance. Differential enzymatic patterns between compartments showed a fast utilization of polysaccharides in the flowing water but a major protein utilization in the ground water. The results of the FI indicated a more terrestrial origin of the larger molecules in the flowing water, also suggesting that transformation of material occurs through the stream-riparian interface. Microbial immobilization and fast utilization of the most biodegradable fraction at the stream-riparian interface is suggested as a relevant DOC retention mechanism just after initial recharging of the ground water compartment. Large and rapid DOC inputs entering the intermittent river system during the transition from drought to precipitation provide available N and C sources for the heterotrophs. Heterotrophs efficiently utilize these resources that were in limited supply during the period of drought. Such changes in C cycling may highlight possible changes in organic matter dynamics under the prediction of extended drying periods in aquatic ecosystems.

Bacteria↗

PubMed2005

Over-expression of tobacco NtHSP70-1 contributes to drought-stress tolerance in plants.

HSP70, a heat shock protein, is a molecular chaperone responsive to various environmental stresses. Here, NtHSP70-1 was a drought-/ABA-inducible gene. We monitored the expression of CaERD15 (early responsive to dehydration) with exposing plants to progressive drought stress. Its activity was used as an indicator of water-deficit conditions. To analyze the protective role of HSP70, we obtained transgenic tobacco plants that constitutively expressed elevated levels of the tobacco HSP70, NtHSP70-1, as well as transgenic plants containing either the vector alone or else having NtHSP70-1 in the antisense orientation. Plants with enhanced levels of NtHSP70-1 in their transgenic sense lines exhibited tolerance to water stress. Under progressive drought, the amount of leaf NtHSP70-1 was correlated with maintenance of optimum water content, with contents being higher in the leaves of dehydrated transgenic sense plants than in those of either the control (vector-only) or the transgenic antisense plants. Moreover, the expression of CaERD15 was considerably reduced in tobacco plants that over-expressed NtHSP70-1. These results suggest that elevated levels of NtHSP70-1 can confer drought-stress tolerance.

Desiccation↗

PubMed2002

The "drought-inducible" histone H1s of tobacco play no role in male sterility linked to alterations in H1 variants.

Tobacco ( Nicotiana tabacum L.) has two major H1 variants (H1A and H1B), which account for over 80% of chromatin linker histones, and four minor variants: H1C, H1D, H1E and H1F. We have shown previously [M. Prymakowska-Bosak et al. (1999) Plant Cell 11:2317-2329] that reversal of the natural proportion of major to minor H1 variants in transgenic tobacco plants results in a characteristic male-sterility phenotype identical to that occurring in many plant species subjected to water deficit at the time of male meiosis. It has been proposed by others that the drought-induced arrest of male gametophyte development is linked to decreased sugar delivery to reproductive tissues. Within the family of angiosperm H1s there is a well-defined class of minor H1 variants named "drought inducible" because some of its members have been shown to be induced by water deficit. We have identified and cloned the tobacco H1C gene, which, based on sequence similarity, represents a "drought-inducible" minor H1 variant. Analysis of the un-translated mRNA and promoter regions of H1C suggests a regulation by sucrose concentration. Antisense silencing of H1C and its close homologue H1D in plants that do not express H1A and H1B does not affect the characteristic H1A(-)/ H1B(-) male-sterility phenotype. Silencing of H1C and H1D also has no effect on growth and development of plants. Our findings demonstrate that H1C and H1D are dispensable for normal growth and development of tobacco, and that the compensatory up-regulation of "drought-inducible" H1s observed in H1A(-)/ H1B(-) plants is not the direct cause of male sterility linked to alterations in H1 variants.

Acclimatization↗

PubMed2004

The ABI2-dependent abscisic acid signalling controls HrpN-induced drought tolerance in Arabidopsis.

HrpN, a protein produced by the plant pathogenic bacterium Erwinia amylovora, has been shown to stimulate plant growth and resistance to pathogens and insects. Here we report that HrpN activates abscisic acid (ABA) signalling to induce drought tolerance (DT) in Arabidopsis thaliana L. plants grown with water stress. Spraying wild-type plants with HrpN-promoted stomatal closure decreased leaf transpiration rate, increased moisture and proline levels in leaves, and alleviated extents of damage to cell membranes and plant drought symptoms caused by water deficiency. In plants treated with HrpN, ABA levels increased; expression of several ABA-signalling regulatory genes and the important effector gene rd29B was induced or enhanced. Induced expression of rd29B, promotion of stomatal closure, and reduction in drought severity were observed in the abi1-1 mutant, which has a defect in the phosphatase ABI1, after HrpN was applied. In contrast, HrpN failed to induce these responses in the abi2-1 mutant, which is impaired in the phosphatase ABI2. Inhibiting wild-type plants to synthesize ABA eliminated the role of HrpN in promoting stomatal closure and reducing drought severity. Moreover, resistance to Pseudomonas syringae developed in abi2-1 as in wild-type plants following treatment with HrpN. Thus, an ABI2-dependent ABA signalling pathway is responsible for the induction of DT but does not affect pathogen defence under the circumstances of this study.

Abscisic Acid↗

PubMed2006

Performance of wheat crops with different chromosome ploidy: root-sourced signals, drought tolerance, and yield performance.

Pot-culture experiments were carried out to estimate the role of non-hydraulic root signals (nHRS) and the relation of these signals to drought tolerance and grain yield formation under drought stress in six wheat varieties. These were two modern hexaploid wheat (Triticum aestivum L., AABBDD) Plateau602 and Longchun8139-2, two diploid wheat (Triticum monococcum L., AB) MO1 and MO4, and two tetraploid wheat (Triticum dicoccum Schuebl L., AABB) DM22 and DM31. In the two diploid relatives, the nHRS was switched on and off at a soil water content (SWC) of approximately 53-45% field water capacity (FWC). In contrast, in the modern hexaploid varieties, Longchun8139-2 and Plateau602 the nHRS occurred between a SWC of about 71 and 35% FWC, a much wider soil moisture range. The two tetraploid relatives, DM22 and DM31, were generally intermediate. The nHRS threshold range in SWC also narrowed as all six varieties went through successive developmental stages from shooting to grain filling. The two hexaploid wheat varieties had the longest duration of survival after the water supply ceased, and the best yield stability under drought stress, similar to with tetraploid wheat varieties; the diploid wheat varieties were least robust. These two parameters were both significantly correlated with the nHRS soil moisture threshold range (r=0.9456** and 0.8608*, respectively). Based on these patterns, we propose a "triple Z" model to describe the features of non-hydraulic stomatal sensitivity versus soil drought in wheat growth.

Crops, Agricultural↗

PubMed2004

Patterns of tree dieback in Queensland, Australia: the importance of drought stress and the role of resistance to cavitation.

During the extreme 1992-1997 El Niño drought event, widespread stem mortality, or tree "dieback", of both mature and juvenile eucalypts occurred within the tropical savannas of northeast Australia. Most of the dieback occurred in individuals of the ironbark species complex ( Eucalyptus crebra- E. xanthoclada) while individuals of the bloodwood species Corymbia erythrophloia, exhibited significantly less stem mortality. Indicative of greater water stress, predawn and midday xylem water potentials of ironbark adults and saplings were significantly more negative than predawn values of bloodwoods. The very negative xylem water potentials in ironbarks suggest that stem mortality in both adult and juvenile ironbarks results from drought-induced embolism and that ironbarks perhaps have a shallower and less extensive root system than bloodwoods. Although predawn and midday water potentials for ironbark adults and saplings were similar, a census of mature and juvenile ironbark trees indicated that mortality was higher in adult trees. Cavitation vulnerability curves indicated that ironbark saplings may be better buffered against cavitation than adult trees. If they possess smaller root systems, saplings are more likely than adults to experience low xylem water potentials, even in non-drought years. Xylem conduits produced in adult trees during periods of normal rainfall, although perhaps more efficient in water conduction, may be more vulnerable to cavitation during infrequent severe droughts.

Adaptation, Physiological↗

PubMed2005

Summer water use by California coastal prairie grasses: fog, drought, and community composition.

Plants in the Mediterranean climate region of California typically experience summer drought conditions, but correlations between zones of frequent coastal fog inundation and certain species' distributions suggest that water inputs from fog may influence species composition in coastal habitats. We sampled the stable H and O isotope ratios of water in non-photosynthetic plant tissue from a variety of perennial grass species and soil in four sites in northern California in order to determine the proportion of water deriving from winter rains and fog during the summer. The relationship between H and O stable isotopes from our sample sites fell to the right of the local meteoric water line (LMWL) during the summer drought, providing evidence that evaporation of water from the soil had taken place prior to the uptake of water by vegetation. We developed a novel method to infer the isotope values of water before it was subjected to evaporation in which we used experimental data to calculate the slope of the deltaH versus deltaO line versus the LMWL. After accounting for evaporation, we then used a two-source mixing model to evaluate plant usage of fog water. The model indicated that 28-66% of the water taken up by plants via roots during the summer drought came from fog rather than residual soil water from winter rain. Fog use decreased as distance from the coast increased, and there were significant differences among species in the use of fog. Rather than consistent differences in fog use by species whose distributions are limited to the coast versus those with broader distributions, species responded individualistically to summer fog. We conclude that fogwater inputs can mitigate the summer drought in coastal California for many species, likely giving an advantage to species that can use it over species that cannot.

California↗

PubMed2005

Drought effects on fine-root and ectomycorrhizal-root biomass in managed Pinus oaxacana Mirov stands in Oaxaca, Mexico.

The effects of a severe drought on fine-root and ectomycorrhizal biomass were investigated in a forest ecosystem dominated by Pinus oaxacana located in Oaxaca, Mexico. Root cores were collected during both the wet and dry seasons of 1998 and 1999 from three sites subjected to different forest management treatments in 1990 and assessed for total fine-root biomass and ectomycorrhizal-root biomass. Additionally, a bioassay experiment with P. oaxacana seedlings was conducted to assess the ectomycorrhizal inoculum potential of the soil for each of the three stands. Results indicated that biomasses of both fine roots and ectomycorrhizal roots were reduced by almost 60% in the drought year compared to the nondrought year. There were no significant differences in ectomycorrhizal and fine-root biomass between the wet and dry seasons. Further, the proportion of total root biomass consisting of ectomycorrhizal roots did not vary between years or seasons. These results suggest that both total fine-root biomass and ectomycorrhizal-root biomass are strongly affected by severe drought in these high-elevation tropical pine forests, and that these responses outweigh seasonal effects. Forest management practices in these tropical pine forests should consider the effects of drought on the capacity of P. oaxacana to maintain sufficient levels of ectomycorrhizae especially when there is a potential for synergistic interactions between multiple disturbances that may lead to more severe stress in the host plant and subsequent reductions in ectomycorrhizal colonization.

Biomass↗

PubMed2005

Impairment of NtAQP1 gene expression in tobacco plants does not affect root colonisation pattern by arbuscular mycorrhizal fungi but decreases their symbiotic efficiency under drought.

We investigated in two tobacco (Nicotiana tabacum) plant lines (wildtype or antisense mutant) whether impairment in expression of the plasma membrane aquaporin gene (NtAQP1) affects the arbuscular mycorrhizal (AM) fungal colonisation pattern or the symbiotic efficiency of AM fungi. These two objectives were investigated under well-watered and drought stress conditions. Both plant lines had a similar pattern of root colonisation under well-watered and drought stress conditions. In contrast, under drought stress, AM wildtype plants grew faster than mycorrhizal antisense plants. Plant gas exchange also appeared to depend on the expression of NtAQP1 and parallelled the determined growth increments. The implications of enhanced symplastic water transport via NtAQP1 for the efficiency of the AM symbiosis under drought stress conditions are further discussed.

Aquaporin 1↗

PubMed2026

Overexpression of the tomato SlLEA_2-26 gene enhances the tolerance to drought and salt stresses in Arabidopsis thaliana.

Late embryogenesis abundant (LEA) proteins are pivotal in conferring cellular tolerance to abiotic stresses and sustaining plant growth and development. However, systematic functional characterization of the tomato SlLEA_2 gene family remains limited. To elucidate the role of tomato SlLEA_2-26 in abiotic stress responses, this study cloned its full-length cDNA. Quantitative real-time PCR (qRT-PCR) analysis revealed that SlLEA_2-26 exhibits predominant expression in flowers and fruits, and is strongly induced by drought, salt, Cu2+, and Pb2+ stresses. Three homozygous Arabidopsis thaliana T3 SlLEA_2-26-overexpression lines were generated and confirmed via genomic PCR. Under drought and salt stress, T3 A. thaliana lines overexpressing SlLEA_2-26 exhibited significantly enhanced seed germination rates, root elongation, and fresh weights compared to wild type (WT) plants, indicating improved stress tolerance during early seedling development. Furthermore, transgenic plants accumulated higher levels of soluble sugar and proline, and displayed elevated antioxidant enzyme activity compared to the WT, whereas contents of malondialdehyde (MDA) and reactive oxygen species (ROS) were markedly reduced relative to WT. qRT-PCR analysis confirmed the significant upregulation of SlLEA_2-26 in transgenic lines under drought and salt stress conditions, accompanied by elevated expression of AtP5CS1, AtCSD1, AtRD29A, AtRD26, and AtNCED3. Collectively, these results demonstrate that SlLEA_2-26 overexpression enhances drought and salt stress tolerance in A. thaliana by promoting the accumulation of osmoregulatory substances, augmenting antioxidant defense capacity, and activating stress-responsive gene expression. This study provides a theoretical foundation and valuable genetic resources for breeding stress-tolerant tomatoes and other crops.

SlLEA_2–26↗

PubMed2006

PIP aquaporin gene expression in arbuscular mycorrhizal Glycine max and Lactuca sativa plants in relation to drought stress tolerance.

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and plant responses to drought still remains elusive. Moreover, the contribution of aquaporin genes to the enhanced tolerance to drought in arbuscular mycorrhisal (AM) plants has never been investigated. Therefore, we studied, at a molecular level, whether the expression of aquaporin-encoding genes in roots is altered by the AM symbiosis as a mechanism to enhance host plant tolerance to water deficit. In this study, genes encoding plasma membrane aquaporins (PIPs) from soybean and lettuce were cloned and their expression pattern studied in AM and nonAM plants cultivated under well-watered or drought stressed conditions. Results showed that AM plants responded to drought stress by down-regulating the expression of the PIP genes studied and anticipating its down-regulation as compared to nonAM plants. The possible physiological implications of this down-regulation of PIP genes as a mechanism to decrease membrane water permeability and to allow cellular water conservation is further discussed.

Aquaporins↗

PubMed2006

A novel drought-inducible gene, ATAF1, encodes a NAC family protein that negatively regulates the expression of stress-responsive genes in Arabidopsis.

NAC proteins are plant-specific transcriptional regulators. ATAF1 was one of the first identified NAC proteins in Arabidopsis. In present study, we characterized the ATAF1 expression and biological function in response to water deficit stress. ATAF1 mRNA expression was strongly induced by dehydration and abscisic acid (ABA) treatment, but inhibited by water treatment, suggesting a general role in drought stress responses. Transient expression analysis in onion epidermal cells indicated the nuclear localization for the ATAF1::GFP fusion protein. Yeast transactivation analysis showed that ATAF1 had ability to activate reporter gene expression. Furthermore, domain deletion analysis revealed that the ATAF1 transactivation activity was conferred by its C-terminal domain. When ATAF1 gene was knocked out by T-DNA insertions, Arabidopsis ataf1-1 and ataf1-2 mutants displayed a recovery rate about seven times higher than wild-type plants in drought response test. This ataf1 phenotype was coincident with the enhanced expression of stress responsive marker genes, such as COR47, ERD10, KIN1, RD22 and RD29A under drought stress. Above evidences suggest that ATAF1, as a transcriptional regulator, negatively regulates the expression of stress responsive genes under drought stress in Arabidopsis.

Arabidopsis↗

PubMed2007

Global genome expression analysis of rice in response to drought and high-salinity stresses in shoot, flag leaf, and panicle.

To elucidate genome-level responses to drought and high-salinity stress in rice, a 70 mer oligomer microarray covering 36,926 unique genes or gene models was used to profile genome expression changes in rice shoot, flag leaf and panicle under drought or high-salinity conditions. While patterns of gene expression in response to drought or high-salinity stress within a particular organ type showed significant overlap, comparison of expression profiles among different organs showed largely organ-specific patterns of regulation. Moreover, both stresses appear to alter the expression patterns of a significant number of genes involved in transcription and cell signaling in a largely organ-specific manner. The promoter regions of genes induced by both stresses or induced by one stress in more than one organ types possess relative enrichment of two cis-elements (ABRE core and DRE core) known to be associated with water stress. An initial computational analysis indicated that novel promoter motifs are present in the promoters of genes involved in rehydration after drought. This analysis suggested that rice might possess a mechanism that actively detects rehydration and facilitates rapid recovery. Overall, our data supports a notion that organ-specific gene regulation in response to the two abiotic stresses may primarily be mediated by organ-specific transcription responses.

DNA Primers↗

PubMed2006

A protective role for the polyamine spermine against drought stress in Arabidopsis.

Cellular polyamine content often changes in response to abiotic stresses. However, its physiological relevance is unknown. We found that an Arabidopsis mutant plant (acl5/spms), which cannot produce spermine, is hypersensitive to high salt. Examination of drought sensitivity of the mutant and comparison with wild type plants indicated hypersensitivity to drought. This phenotype was cured by spermine pretreatment but not by the other polyamines putrescine and spermidine, suggesting that drought-hypersensitivity exhibited by the mutant is due to spermine deficiency. The water loss rate of wild type and mutant plants were similar until 20 min after onset of dehydration stress, but after a longer exposure the rate in mutant plants was higher than in wild type plants. Consistent with this result, the stomata of the mutant leaves remained open while in wild type leaves they closed. Based on the collected data, we discuss a role for spermine in response to drought stress.

Arabidopsis↗