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At least 19 recordsLinked to original sources
PubMed2002

Effect of drought stress on the yield and composition of volatile oils of drought-tolerant and non-drought-tolerant clones of Tagetes minuta.

A drought-tolerant clone of Tagetes minuta L. (Asteraceae) was selected in vitro on a medium containing 60 mM mannitol. In the greenhouse, a decrease in soil field capacity (FC) from 100 to 40 % reduced oil yield by 49, 71 and 71 % for drought-tolerant, non-drought tolerant cloned and seed-grown plants, respectively. In soil at 40 % FC, the drought-tolerant clone had the highest leaf dry weight and oil yield. At 100 % FC, there was no significant difference in leaf dry weight, but the drought-tolerant clone had a significantly higher percentage oil content and yield than seed-grown plants. The main components of the oil were monoterpenes of which trans- and cis-tagetone together were 52.3 % - 64.2 %. Drought significantly altered the content of some oil components.

Acclimatization↗
PubMed2005

Genetic basis of drought resistance at reproductive stage in rice: separation of drought tolerance from drought avoidance.

Drought tolerance (DT) and drought avoidance (DA) are two major mechanisms in drought resistance of higher plants. In this study, the genetic bases of DT and DA at reproductive stage in rice were analyzed using a recombinant inbred line population from a cross between an indica lowland and a tropical japonica upland cultivar. The plants were grown individually in PVC pipes and two cycles of drought stress were applied to individual plants with unstressed plants as the control. A total of 21 traits measuring fitness, yield, and the root system were investigated. Little correlation of relative yield traits with potential yield, plant size, and root traits was detected, suggesting that DT and DA were well separated in the experiment. A genetic linkage map consisting of 245 SSR markers was constructed for mapping QTL for these traits. A total of 27 QTL were resolved for 7 traits of relative performance of fitness and yield, 36 QTL for 5 root traits under control, and 38 for 7 root traits under drought stress conditions, suggesting the complexity of the genetic bases of both DT and DA. Only a small portion of QTL for fitness- and yield-related traits overlapped with QTL for root traits, indicating that DT and DA had distinct genetic bases.

Analysis of Variance↗
PubMed2006

Identification of drought tolerance determinants by genetic analysis of root response to drought stress and abscisic Acid.

Drought stress is a common adverse environmental condition that seriously affects crop productivity worldwide. Due to the complexity of drought as a stress signal, deciphering drought tolerance mechanisms has remained a major challenge to plant biologists. To develop new approaches to study plant drought tolerance, we searched for phenotypes conferred by drought stress and identified the inhibition of lateral root development by drought stress as an adaptive response to the stress. This drought response is partly mediated by the phytohormone abscisic acid. Genetic screens using Arabidopsis (Arabidopsis thaliana) were devised, and drought inhibition of lateral root growth (dig) mutants with altered responses to drought or abscisic acid in lateral root development were isolated. Characterization of these dig mutants revealed that they also exhibit altered drought stress tolerance, indicating that this root response to drought stress is intimately linked to drought adaptation of the entire plant and can be used as a trait to access the elusive drought tolerance machinery. Our study also revealed that multiple mechanisms coexist and together contribute to whole-plant drought tolerance.

Abscisic Acid↗
PubMed2002

Linking drought-resistance mechanisms to drought avoidance in upland rice using a QTL approach: progress and new opportunities to integrate stomatal and mesophyll responses.

The advent of saturated molecular maps promised rapid progress towards the improvement of crops for genetically complex traits like drought resistance via analysis of quantitative trait loci (QTL). Progress with the identification of QTLs for drought resistance-related traits in rice is summarized here with the emphasis on a mapping population of a cross between drought-resistant varieties Azucena and Bala. Data which have used root morphological traits and indicators of drought avoidance in field-grown plants are reviewed, highlighting problems and uncertainties with the QTL approach. The contribution of root-growth QTLs to drought avoidance appears small in the experiments so far conducted, and the limitations of screening methodologies and the involvement of shoot-related mechanisms of drought resistance are studied. When compared to Azucena, Bala has been observed to have highly sensitive stomata, does not roll its leaves readily, has a greater ability to adjust osmotically, slows growth more rapidly when droughted and has a lower water-use efficiency. It is also a semi-dwarf variety and hence has a different canopy structure. There is a need to clarify the contribution of the shoot to drought resistance from the level of the biochemistry of photosynthesis through stomatal behaviour and leaf anatomy to canopy architecture. Recent advances in studying the physical and biochemical processes related to water use and drought stress offer the opportunity to advance a more holistic understanding of drought resistance. These include the potential use of infrared thermal imaging to study energy balance, integrated and online stable isotope analysis to dissect processes involved in carbon dioxide fixation and water evaporation, and leaf fluorescence to monitor photosynthesis and photochemical quenching. Justification and a strategy for this integrated approach is described, which has relevance to the study of drought resistance in most crops.

Adaptation, Physiological↗
PubMed1998

Molecular and physiological responses to water deficit in drought-tolerant and drought-sensitive lines of sunflower. Accumulation of dehydrin transcripts correlates with tolerance.

To investigate correlations between phenotypic adaptation to water limitation and drought-induced gene expression, we have studied a model system consisting of a drought-tolerant line (R1) and a drought-sensitive line (S1) of sunflowers (Helianthus annuus L.) subjected to progressive drought. R1 tolerance is characterized by the maintenance of shoot cellular turgor. Drought-induced genes (HaElip1, HaDhn1, and HaDhn2) were previously identified in the tolerant line. The accumulation of the corresponding transcripts was compared as a function of soil and leaf water status in R1 and S1 plants during progressive drought. In leaves of R1 plants the accumulation of HaDhn1 and HaDhn2 transcripts, but not HaElip1 transcripts, was correlated with the drought-adaptive response. Drought-induced abscisic acid (ABA) concentration was not associated with the varietal difference in drought tolerance. Stomata of both lines displayed similar sensitivity to ABA. ABA-induced accumulation of HaDhn2 transcripts was higher in the tolerant than in the sensitive genotype. HaDhn1 transcripts were similarly accumulated in the tolerant and in the sensitive plants in response to ABA, suggesting that additional factors involved in drought regulation of HaDhn1 expression might exist in tolerant plants.

Abscisic Acid↗
PubMed2002

Effect of drought on the growth and survival of the stress-tolerant bacterium Rhizobium sp. NBRI2505 sesbania and its drought-sensitive transposon Tn 5 mutant.

Studies were conducted to elucidate the nature of drought tolerance in the bacterium Rhizobium sp. NBRI2505 sesbania and its transposon Tn 5 induced mutant to assess the role of salt, pH, and temperature stresses in contributing to drought tolerance, and to correlate drought tolerance and symbiotic effectiveness. Rhizobium sp. NBRI2505 sesbania tolerated yeast extract mannitol broth (YEB) containing 28% salt (NaCl; wt/vol) for up to 18 h of incubation at 30 degrees C, survived a 2-h incubation in YEB at 65 degrees C, and when subjected to drought stress, tolerated YEB containing 45% polyethylene glycol 6000 (PEG; wt/vol) for up to 5 days of incubation at 30 degrees C. One drought-sensitive mutant Rhizobium sp. NBRI2505 sesbania T112 (T112) containing a single Tn 5 insertion was selected after screening about 10,000 clones. T112 was specifically defective in its tolerance for drought: when subjected to drought stress, it tolerated YEB containing 45% PEG for up to 2 days of incubation at 30 degrees C. T122 mutant was also more sensitive to the heat and desiccation stresses, compared with Rhizobium sp. NBRI2505 sesbania in the presence of 45% PEG. Our results demonstrated a positive effect of calcium on the survival of Rhizobium sp. sesbania under acidic stress conditions. The observed enhanced survival at pH 3 of Rhizobium sp. NBRI2505 sesbania and T112 in the presence of 5% CaCO(3) suggests the requirement of calcium for growth and survival, which may have an ecological significance in acidic soils. Mutant strain T112 produced ineffective symbiosis with the plant host in the presence of 2.5 and 5% PEG, indicating that drought tolerance is required for effective symbiosis.

DNA Transposable Elements↗
PubMed2004

Drought tolerance and transplanting performance of holm oak (Quercus ilex) seedlings after drought hardening in the nursery.

Drought stress is the main cause of mortality of holm oak (Quercus ilex L.) seedlings in forest plantations. We therefore assessed if drought hardening, applied in the nursery at the end of the growing season, enhanced the drought tolerance and transplanting performance of holm oak seedlings. Seedlings were subjected to three drought hardening intensities (low, moderate and severe) for 2.5 and 3.5 months, and compared with control seedlings. At the end of the hardening period, water relations, gas exchange and morphological attributes were determined, and survival and growth under mesic and xeric transplanting conditions were assessed. Drought hardening increased drought tolerance primarily by affecting physiological traits, with no effect on shoot/root ratio or specific leaf mass. Drought hardening reduced osmotic potential at saturation and at the turgor loss point, stomatal conductance, residual transpiration (RT) and new root growth capacity (RGC), but enhanced cell membrane stability. Among treated seedlings, the largest response occurred in seedlings subjected to moderate hardening. Severe hardening reduced shoot soluble sugar concentration and increased shoot starch concentration. Increasing the duration of hardening had no effect on water relations but reduced shoot mineral and starch concentrations. Variation in cell membrane stability, RT and RGC were negatively related to osmotic adjustment. Despite differences in drought tolerance, no differences in mortality and relative growth rate were observed between hardening treatments when the seedlings were transplanted under either mesic or xeric conditions.

Dehydration↗
PubMed1988

Influence of Drought Acclimation and CO(2) Enrichment on Osmotic Adjustment and Chlorophyll a Fluorescence of Sunflower during Drought.

Osmotic adjustment occurred during drought in expanded leaves of sunflowers (Helianthus annuus var Hysun 30) which had been continuously exposed to 660 microliters CO(2) per liter or had been previously acclimated to drought. The effect was greatest when the treatments were combined and was negligible in nonacclimated plants grown at 340 microliters CO(2) per liter. The concentrations of ethanol soluble sugars and potassium increased during drought but they did not account for the osmotic adjustment. The delay in the decline in conductance and relative water content and in the loss of structural integrity with increasing drought was dependent on the degree of osmotic adjustment. Where it was greatest, conductance fell from 5.8 millimeters per second on the first day of drought to 1.3 millimeters per second on the fourth day and was at approximately the same level on the eighth day. The relative water content remained constant at 85% for three days and fell to 36% on the sixth day. There was no evidence of leaf desiccation even on the eighth day. In contrast, the conductance of leaves showing minimal adjustment fell rapidly after the first day of drought and was negligible after the fourth, at which time the relative water content was 36%. By the sixth day of drought, areas near the margins of the leaves were desiccating and the plants did not recover upon rewatering. Despite the differences in the rate of change of conductance and relative water content during drought, photosynthetic electron transport activity, inferred from measurements of chlorophyll a fluorescence in vivo and PSII activity of isolated thylakoids, remained functional until desiccation occurred.

Journal Article↗
PubMed1994

Regulation of pea cytosolic ascorbate peroxidase and other antioxidant enzymes during the progression of drought stress and following recovery from drought.

The molecular mechanism underlying the regulation of the expression of Apxl, the gene encoding cytosolic ascorbate peroxidase, as well as other antioxidant enzymes, was studied during the progression of drought stress and following recovery from drought. Increase in steady-state transcript levels of the cytosolic isozymes of ascorbate peroxidase and Cu/Zn-superoxide dismutase paralleled the increase in stomatal resistance during drought stress, but was even more dramatically enhanced following recovery from drought. Cytosolic Cu/Zn-superoxide dismutase and ascorbate peroxidase and chloroplastic Cu/Zn-superoxide dismutase protein and activity increased during drought stress and following recovery. In contrast, catalase activity increased during drought stress but returned to normal levels following recovery. During recovery from drought stress, cytosolic ascorbate peroxidase expression was regulated post-transcriptionally at the level of protein synthesis. The transcription rate of the Apxl gene, as determined by nuclear run-on assay, increased during drought stress and at 10 h following rewatering.

Ascorbate Peroxidases↗
PubMed2000

Energy dissipation in drought-avoiding and drought-tolerant tree species at midday during the Mediterranean summer.

Photosynthetic performance was monitored during two consecutive summers in four co-occurring evergreen Mediterranean tree species growing on a south-facing rocky slope. In response to midday water stress, the drought-avoiding species Pinus halepensis Mill. exhibited marked stomatal closure (g(s)) but no changes in stem water potential (Psi(s)), whereas the drought-tolerant species Quercus coccifera L., Q. ilex ssp. ballota (Desf.) Samp. and Juniperus phoenicea L. displayed declines in midday g(s) and Psi(s). The higher resistance to CO(2) influx in needles of P. halepensis compared with the other species did not result in either a proportional increase in non-radiative dissipation of excess energy or photo-inactivation of photosystem II (PSII). No significant differences were found among species either in the de-epoxidation state of the xanthophyll cycle (DPS) or in the pool of its components on a total chlorophyll basis (VAZ). Despite contrasting midday assimilation rates, the three drought-tolerant species all exhibited a pronounced drop in photochemical efficiency at midday that was characterized by a decrease in the excitation capture efficiency of the open PSII centers. Although photoinhibition was not fully reversed before dawn, it apparently did not result in cumulative photo-damage. Thus, the drought-avoiding and drought-tolerant species employed different mechanisms for coping with excess light during the midday depression in photosynthesis that involved contrasting midday photochemical efficiencies of PSII and different degrees of dynamic photoinhibition as a photo-protective mechanism. These behaviors may be related to the different mechanisms employed by drought-avoiding and drought-tolerant species to withstand water deficit.

Journal Article↗
PubMed1993

Characterization of Expression of Drought- and Abscisic Acid-Regulated Tomato Genes in the Drought-Resistant Species Lycopersicon pennellii.

A number of genes are induced by drought stress, and some of these genes are regulated by the plant hormone abscisic acid (ABA). In tomato (Lycopersicon esculentum), four genes have been identified and isolated that require elevated levels of endogenous ABA for expression: le4, le16, le20, and le25. To gain a better understanding of the role of these genes during stress, their expression has been studied in the drought-resistant relative of tomato, Lycopersicon pennellii. It was determined that homologous genes to all four of the L. esculentum genes were present in the L. pennellii genome. Studies were undertaken to compare the expression characteristics of these genes in L. esculentum, L. pennellii, and their F1. Using two methods of water-deficit imposition, whole plants to which water was withheld and detached leaves that were wilted to 88% of their original fresh weight, it was demonstrated that transcripts of these genes accumulated in L. pennellii in response to water deficit. In general, the increase occurred after a longer period of water deficit in L. pennellii than in tomato. As in drought-sensitive species, ABA levels were elevated by drought stress in L. pennellii, although the levels were reduced compared with those in tomato. All four tomato genes were responsive to ABA in L. esculentum and the F1, but only three of the four genes (le16, le20, and le25) were induced in response to exogenous application of ABA in L. pennellii. The patterns of expression of these genes in L. pennellii are generally similar to that of L esculentum; therefore, it is suggested that these genes play a similar, yet undefined, role in both genotypes rather than being genes that are responsible for the greater drought resistance of L. pennellii.

Journal Article↗
PubMed1996

Novel drought-inducible genes in the highly drought-tolerant cowpea: cloning of cDNAs and analysis of the expression of the corresponding genes.

Ten cDNAs of genes that were induced by dehydration stress were cloned by differential screening from the highly drought-tolerant legume, cowpea (Vigna unguiculata), a major crop in West Africa. The clones were collectively named CPRD (cowpea clones responsive to dehydration). Northern blot analysis revealed that nine of the CPRD genes were induced by dehydration stress, but the timing of induction of mRNA synthesis varied among the CPRD genes. We analyzed the effects of other environmental stresses on the expression of the CPRD8, CPRD14 and CPRD22 genes, and we found that these genes were strongly induced by high-salinity stress but not by cold or heat stress. Drought-stressed cowpea plants accumulated abscisic acid (ABA) to a level that was 160 times higher than that in unstressed plants. The CPRD8 and CPRD22 genes were induced to a significant extent by the application of exogenous ABA but the CPRD14 gene was not. These results indicate the existence of at least two signal-transduction pathways between the detection of water stress and the expression of CPRD genes in cowpea. Sequence analysis of CPRD8 and CPRD22 cDNAs revealed that they encoded putative proteins that were related to old yellow enzyme and group 2 LEA proteins, respectively. The protein encoded by CPRD14 exhibited sequence homology to dihydroflavonol-4-reductase (DFR) and vestitone reductase (VR). Old yellow enzyme, DFR and VR have not been identified as drought-inducible proteins in other plants, whereas LEA genes have been well characterized as drought-inducible genes. The various gene products might function to protect cells from environmental stress.

Abscisic Acid↗
PubMed1994

Does drought increase migration? A study of migration from rural Mali during the 1983-1985 drought.

"Using data from a longitudinal panel study conducted in 1982 and 1989 in...Mali, this article demonstrates that the level of migration did not rise during the drought of 1983-1985. However, there was a dramatic increase in the migration of women and children during the severe 1983-1985 drought. Along with this increase in migration by women and children, there was a shift to short-cycle circulation, with 64 percent of the migrants adopting circular patterns. The study describes the characteristics of these migrants and recommends changes to development and migration policies that will facilitate such migrations in subsequent droughts."

Africa↗
PubMed2000

Gender and drought: experiences of Australian women in the drought of the 1990s.

A unique collaborative, sociological study undertaken during 1995-7, explored the social construction of drought as a disaster, looking at farm families in two Australian states: Queensland (beef producers) and New South Wales (sheep/wheat producers). A decision was made to interview the women and men separately to test our hypothesis that there would be gender issues in any analysis of a disaster, but particularly one which has had so much long-term impact on individuals, families and communities, such as drought. Interviews were conducted with over 100 individuals male and female. We conclude that drought as a disaster is a gendered experience. The paper draws on the narratives of some women involved in the study to identify 'themes of difference' which confirm the necessity to maintain gender as a variable in all studies of the social impacts of disaster.

Adaptation, Psychological↗
PubMed1995

The role of food aid in drought and recovery: Oxfam's North Turkana (Kenya) drought relief programme, 1992-94.

Regional droughts carry the seeds of catastrophe: the immediate risk is famine; the long-term risk is destitution. Preventing both situations is an appropriate, if not essential, goal for relief agencies. In the past, responses to hunger in Turkana District (north-west Kenya) have taken the form of traditional feeding programmes. A better understanding of the boom/bust cycles in pastoralist systems has, however, produced new relief strategies. A central tenet of these strategies is the acceptance that relief aid should assume two roles: humanitarian--to overcome food deficits--and economic--to overcome 'income' deficits. Arguments in favour of a broader role for food aid are tested with a case study of a drought relief programme in north Turkana between 1992-1994. Field studies confirmed that when food aid is integrated as an asset into household resources, it can strengthen economic recovery. Ultimately, the extent to which relief operations are able to protect both people's lives and their livelihoods is the key to more sustainable development in drought-prone areas.

Adult↗
PubMed1977

Water Stress and Protein Synthesis: V. Protein Synthesis, Protein Stability, and Membrane Permeability in a Drought-sensitive and a Drought-tolerant Moss.

The effects have been studied of water stress and desiccation on protein synthesis in the drought-tolerant moss Tortula ruralis and the drought-sensitive moss Hygrohypnum luridum. At any particular level of steady state water stress, the inhibition of protein synthesis was greater in H. luridum than in T. ruralis. Water stress-induced changes in the pattern of protein synthesis, as determined by the double label ratio technique, were minor in T. ruralis, but major in H. luridum. Proteins of both mosses were found to be stable during desiccation and subsequent rehydration. Changes in membrane permeability, as indicated by the leakage of amino acid, were observed during rehydration of desiccated moss and were dependent on the rate of desiccation. The leakage was small and reversible in T. ruralis but large and irreversible in H. luridum. Although H. luridum failed to recover from complete desiccation (80% loss in fresh weight), it was able to recover fully from steady state stress under conditions where a maximum loss of 55% in fresh weight was recorded.

Journal Article↗
PubMed1989

[Resistance to drought of mollusks of the genus Bulinus, vectors of human and animal trematode infections in Senegal. II. Study under natural conditions in the North-Sudan area. Ecology and resistance to drought of Bulinus umbilicatus and B. senegalensis].

The authors report on the results of a 2-year study on the ecology and resistance to drought of B. umbilicatus and B. senegalensis on 3 temporary ponds in the North-Sudan area (region of Tambacounda, Senegal). The variations in some abiotic factors like the temperature and the pH of water do not seem to have a strong influence on the ecology while rainfall has a great importance on the distribution and the density of molluscs. As a fact, the quantity of water and the drying out period of these ponds depend upon rain factors which rule the existence and the survival of the malacological fauna. In the second part of the rainy season, the population reaches its maximum, i.e., during the reproduction period. Monthly observations show that the relative abundance of B. umbilicatus is higher than that of B. senegalensis. These ponds are dry during 6 to 8 months per year. However the populations of molluscs regenerate regularly, a fact which presupposes a certain ability to resist drought. Some come through this period successfully, but the middle-sized ones (7 to 9.9 mm) resist better than others (70 to 80 per cent of the population). Immediately after the first rains they resume their activity and lay intensively in order to reconstitute the population. B. umbilicatus and B. senegalensis are potential intermediate hosts for human and animal trematode infections, but in the studied region only B. umbilicatus intervenes in the transmission of S. haematobium and S. curassoni which occurs between September and November. Under natural Sahel conditions the epidemiological cycle is short and everything happens within 4 to 6 months with the regeneration and the growth of the population of molluscs, its infestation and the transmission of trematode infections. The ecological behaviour of these molluscs in the North-Sudan region is very important in the epidemiology of human and animal trematode infections and requires a new controlling strategy. The destruction of molluscs is more effective and more economic at the end of the rain season, which is the beginning of the drying of ponds, a period in which they concentrate in the residual water pools.

Animals↗
PubMed2001

Enhanced drought tolerance of a soil-dwelling springtail by pre-acclimation to a mild drought stress.

The springtail Folsomia candida has a highly permeable cuticle, but is able to survive several weeks at 98.2%RH. This corresponds to a water potential deficit of about 17bars between the environment and the normal osmotic pressure of the body fluids of this animal. Recent studies have shown a water vapour absorption mechanism by accumulation of sugars and polyols (SP) in F. candida, which explains how this species can survive dehydrating conditions. In the present study, adult F. candida were pre-acclimated at 98.2%RH to induce the accumulation of SP, and were subsequently exposed for additional desiccating conditions from 98 to 94%RH. Activity level, water content, osmotic pressure of body fluids and SP composition were investigated. After the desiccation period, the animals were rehydrated at 100%RH and survival was assessed. The results showed that F. candida survived a more severe drought stress when it had been pre-acclimated to 98.2%RH before exposure to lower humidity. This species was able to maintain hyperosmosity to the surroundings at 95.5%RH, suggesting that it can absorb water vapour down to this limit. Below this limit, trehalose levels increased while myo-inositol levels decreased. We propose that this is a change of survival strategy where F. candida at mild desiccation levels seek to retain water by colligative means (remain hyperosmotic), but at severe desiccation levels switches to an anhydrobiotic strategy.

Journal Article↗