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PubMed2001

Drought- and salt-tolerant plants result from overexpression of the AVP1 H+-pump.

Transgenic plants overexpressing the vacuolar H(+)-pyrophosphatase are much more resistant to high concentrations of NaCl and to water deprivation than the isogenic wild-type strains. These transgenic plants accumulate more Na(+) and K(+) in their leaf tissue than the wild type. Moreover, direct measurements on isolated vacuolar membrane vesicles derived from the AVP1 transgenic plants and from wild type demonstrate that the vesicles from the transgenic plants have enhanced cation uptake. The phenotypes of the AVP1 transgenic plants suggest that increasing the vacuolar proton gradient results in increased solute accumulation and water retention. Presumably, sequestration of cations in the vacuole reduces their toxic effects. Genetically engineered drought- and salt-tolerant plants could provide an avenue to the reclamation of farmlands lost to agriculture because of salinity and a lack of rainfall.

Abscisic Acid↗
PubMed1998

Stomatal plugs of Drimys winteri (Winteraceae) protect leaves from mist but not drought.

Two outstanding features of the flowering plant family Winteraceae are the occlusion of their stomatal pores by cutin plugs and the absence of water-conducting xylem vessels. An adaptive relationship between these two unusual features has been suggested whereby stomatal plugs restrict gas exchange to compensate for the presumed poor conductivity of their vesselless wood. This hypothesized connection fueled evolutionary arguments that the vesselless condition is ancestral in angiosperms. Here we show that in Drimys winteri, a tree common to wet forests, these stomatal occlusions pose only a small fixed resistance to water loss. In addition, they modify the humidity response of guard cells such that under high evaporative demand, leaves with plugs lose water at a faster rate than leaves from which the plugs have been experimentally removed. Instead of being adaptations for drought, we present evidence that these cuticular structures function to maintain photosynthetic activity under conditions of excess water on the leaf surface. Stomatal plugs decrease leaf wettability by preventing the formation of a continuous water film that would impede diffusion of CO2 into the leaf. Misting of leaves had no effect on photosynthetic rate of leaves with plugs, but resulted in a marked decrease ( approximately 40%) in leaves from which the plugs had been removed. These findings do not support a functional association between stomatal plugs and hydraulic competence and provide a new perspective on debates surrounding the evolution of vessels in angiosperms.

Journal Article↗
PubMed1998

Drought-induced shift of a forest-woodland ecotone: rapid landscape response to climate variation.

In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects-particularly those caused by mortality-largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and pinon-juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.

Journal Article↗
PubMed2006

Regulating the drought-responsive element (DRE)-mediated signaling pathway by synergic functions of trans-active and trans-inactive DRE binding factors in Brassica napus.

DREB1/C-repeat binding factor (CBF) is a plant-specific family of transcription factors and plays a crucial role in freeze tolerance. In the present work, two groups of drought-responsive element binding factor (DREB)-like genes were isolated from Brassica napus, named Group I and Group II. The two groups of genes were both induced by low temperature, but the expression of Group I preceded that of Group II. The Group I DREBs could specifically bind with the DRE cis-acting element and activate the expression of downstream genes, but Group II factors were trans-inactive although they still had the ability to bind with DRE, which was confirmed by electrophoretic mobility shift assay. Fluorescence quenching assays indicated that the DRE binding ability of the two groups was similar. Co-expression of Group II could depress the trans-activation activity of Group I DREB in a concentration-dependent manner. These results strongly suggested that the trans-active Group I DREBs were expressed at the early stage of cold stress to open the DRE-mediated signaling pathway in cold stress, whereas the trans-inactive Group II DREBs were expressed at the later stage to close the signal pathway in a competitive manner. The results herein provide a new insight into the regulation mechanisms of the DRE-mediated signaling pathway in response to cold stress.

Amino Acid Sequence↗
PubMed2005

Maternal micronutrient status and decreased growth of Zambian infants born during and after the maize price increases resulting from the southern African drought of 2001-2002.

OBJECTIVE: To investigate the effects on maternal micronutrient status and infant growth of the increased maize prices that resulted from the southern African drought of 2001-2002. DESIGN: Longitudinal cohort study. SETTING: A maternal and child health clinic in Lusaka, Zambia. SUBJECTS: Maternal and infant health and nutrition data and maternal plasma were being collected for a study of breast-feeding and postpartum health. Samples and data were analysed according to whether they were collected before (June to December 2001), during (January 2002 to April 2003) or after (May 2003 to January 2004) the period of increased maize price. Season and maternal HIV status were controlled for in analyses. RESULTS: Maize price increases were associated with decreased maternal plasma vitamin A during pregnancy (P = 0.028) and vitamin E postpartum (P = 0.042), with the lowest values among samples collected after May 2003 (vitamin A: 0.96 micromol l(-1), 95% confidence interval (CI) 0.84-1.09, n = 38; vitamin E: 30.8 micromol mmol(-1) triglycerides, 95% CI 27.2-34.8, n = 64) compared with before January 2002 (vitamin A: 1.03 micromol l(-1), 95% CI 0.93-1.12, n = 104; vitamin E: 38.9 micromol mmol(-1) triglycerides, 95% CI 34.5-43.8, n = 47). There were no significant effects of sampling date on maternal weight, haemoglobin or acute-phase proteins and only marginal effects on infant weight. Infant length at 6 and 16 weeks of age decreased progressively throughout the study (P-values for time of data collection were 0.51 at birth, 0.051 at 6 weeks and 0.026 at 16 weeks). CONCLUSIONS: The results show modest effects of the maize price increases on maternal micronutrient status. The most serious consequence of the price increases is likely to be the increased stunting among infants whose mothers experienced high maize prices while pregnant. During periods of food shortages it might be advisable to provide micronutrient supplements even to those who are less food-insecure.

Cohort Studies↗
PubMed2002

Interpreting changes in heroin supply in Melbourne: droughts, gluts or cycles?

In this Harm Reduction Digest Paul Dietze and John Fitzgerald provide another possible way of understanding what has come to be referred to as Australia's heroin 'drought'. They examine evidence from Melbourne, Victoria and suggest that the apparent downturn in heroin availability in 2000 may, in part, be the result of an end of a heroin 'glut' and that perceptions of this phenomenon may be coloured by the development of more sophisticated indicators of the heroin market. They conclude with claims that the reasons for the reduction in drug consumption and adverse health outcomes, such as those attributed to interdiction, are thus premature

Heroin↗
PubMed2000

Energy and micronutrient composition of dietary and medicinal wild plants consumed during drought. Study of rural Fulani, northeastern Nigeria.

Two rural settled Fulani villages, northeastern Nigeria, were surveyed for dietary practices and use of edible wild plants (n = 100 households). Commonly consumed species of edible wild barks, fruits, leaves, nuts, seeds, and tubers were analyzed for protein, fat, and carbohydrate and for minerals. Kuka bark (Adansonia digitata) given to infants to increase weight gain was high in fat, calcium, copper, iron, and zinc. Cediya (Ficus thonningii), dorowa (Parkia biglobosa) and zogale (Moringa oleifera) were good sources of protein and fat and excellent sources of calcium and iron or copper and zinc. Fruits, leaves, and nuts of aduwa (Balanites aegyptiaca) were widely used during the dry season and during drought. Edible wild species available during the wet season generally were inferior in energy and micronutrient mineral content compared to dry season plants. Fruits commonly eaten by children were poor sources of protein and minerals but rich in carbohydrate and fiber. Tsamiya seeds (Tamarindus indica) were good sources of zinc and used to make dawwa (porridge) commonly consumed during pregnancy. Kirya seeds (Prosopos africana) contained the highest zinc concentrations. Shiwaka leaves (Veronia colorate) consumed by pregnant women to increase breastmilk production and to expel intestinal worms, were high in fiber, phosphorus, magnesium, manganese, and were adequate sources of calcium.

Diet↗
PubMed2000

Influence of Drought-Induced Water Stress on Soybean and Spinach Leaf Ascorbate-Dehydroascorbate level and Redox Status.

We examined the influence of water stress (water deficit) induced by drought on the steady state levels of ascorbic acid (ASC), dehydroascorbate (DHA), and the ASC&rcolon;DHA redox status in leaflets of Glycine max (soybean) and leaves of Spinacia oleracea (spinach). Two soybean cultivars (cv. Essex and cv. Forrest) and one spinach cultivar (cv. Nordic) were grown in high-light growth chambers ( approximately 1000-1200 µmol m-2 s-1) or in the greenhouse during May, June, and July 1999. The cultivars were supplied with water until approximately 25-29 d postemergence, at which time one-half of the plants were not watered for a period of from 4.5 to 7.5 d; the other half of the plants were provided water daily and served as controls. On designated days, leaf water potential (PsiLeaf) was measured, and leaf disks of constant area were excised in the period between approximately 1230 and 1330 hours. Leaf disk samples were immediately frozen in liquid N2, samples were extracted, and ASC and DHA levels were measured and expressed as µmol per gram dry mass per time point. For the soybean cultivars, low PsiLeaf values ( approximately -3.00 to -3.95 MPa) were accompanied by slight decreases in ASC levels and slight increases in DHA levels per gram dry mass. In some cases, leaflet ASC levels of water-stressed soybeans were similar to controls or were even increased by as much as 1.2 times. In soybeans, the mole fraction of ASC remained at 93-99 mol% of the total ascorbate (ASC+DHA), indicating that most of the total ascorbate remained in the reduced form even at low water potential. In spinach plants subjected to water stress (-1.8 to -2.6 MPa), leaf ASC decreased as much as 38%, but the ASC remained at 96-99 mol% of the total ascorbate. It is concluded that during water stress, enzymes of the ascorbate-glutathione cycle in leaf mesophyll cells, as well as in the system that generates reductant to support DHA to ASC recycling, e.g., photosynthetic electron transport in chloroplasts, is able to remain active enough to maintain reduction of DHA to ASC.

Journal Article↗
PubMed2002

Mapping QTLs regulating morpho-physiological traits and yield: case studies, shortcomings and perspectives in drought-stressed maize.

Comparative analysis of a number of studies in drought-stressed maize (Zea mays L.) reporting quantitative trait loci (QTLs) for abscisic acid concentration, root characteristics, other morpho-physiological traits (MPTs) and grain yield (GY) reveals their complex genetic basis and the influence of the genetic background and the environment on QTL effects. Chromosome regions (e.g. near umc11 on chromosome 1 and near csu133 on chromosome 2) with QTLs controlling a number of MPTs and GY across populations and conditions of different water supply have been identified. Examples are presented on the use of QTL information to elucidate the genetic and physiological bases of the association among MPTs and GY. The QTL approach allows us to develop hypotheses accounting for these associations which can be further tested by developing near isogenic lines (NILs) differing for the QTL alleles. NILs also allow for a more accurate assessment of the breeding value of MPTs and, in some cases, may allow for the map-based cloning of the gene(s) underlying the QTL. Although QTL analysis is still time-consuming and resource-demanding, its integration with genomics and post-genomics approaches (e.g. transcriptome, proteome and metabolome analyses) will play an increasingly important role for the identification and validation of candidate genes affecting MPTs and GY.

Abscisic Acid↗
PubMed2003

Development and structure of drought-tolerant leaves of the Mediterranean shrub Capparis spinosa L.

Capparis spinosa (caper), a winter-deciduous perennial shrub, is a consistent floristic element of Mediterranean ecosystems, growing from May to October, i.e. entirely during the prolonged summer drought. The internal architecture of young and fully expanded leaves was studied, along with certain physiological characteristics. Capparis spinosa possesses thick, amphistomatic and homobaric leaves with a multilayered mesophyll. The latter possesses an increased number of photosynthesizing cells per unit leaf surface, a large surface area of mesophyll cells facing intercellular spaces (Smes) and a low percentage of intercellular space per tissue volume. Smes and chlorophyll content attain their maximum values synchronously, slightly before full leaf expansion. Nitrogen investment is also completed before full leaf expansion. The structural features, in combination with the water status, could contribute to enhanced rates of transpiration and photosynthesis under field water shortage conditions.

Adaptation, Physiological↗
PubMed2003

Photosynthetic responses of the tropical spiny shrub Lycium nodosum (Solanaceae) to drought, soil salinity and saline spray.

Water relations and photosynthetic characteristics of plants of Lycium nodosum grown under increasing water deficit (WD), saline spray (SS) or saline irrigation (SI) were studied. Plants of this perennial, deciduous shrub growing in the coastal thorn scrubs of Venezuela show succulent leaves which persist for approx. 1 month after the beginning of the dry season; leaf succulence is higher in populations closer to the sea. These observations suggested that L. nodosum is tolerant both to WD and salinity. In the glasshouse, WD caused a marked decrease in the xylem water potential (psi), leaf osmotic potential (psi(s)) and relative water content (RWC) after 21 d; additionally, photosynthetic rate (A), carboxylation efficiency (CE) and stomatal conductance (gs) decreased by more than 90 %. In contrast, in plants treated for 21 d with a foliar spray with 35 per thousand NaCl or irrigation with a 10 % NaCl solution, psi and RWC remained nearly constant, while psi(s) decreased by 30 %, and A, CE and gs decreased by more than 80 %. An osmotic adjustment of 0.60 (SS) and 0.94 MPa (SI) was measured. Relative stomatal and mesophyll limitations to A increased with both WD and SS, but were not determined for SI-treated plants. No evidence of chronic photoinhibition due to any treatment was observed, since maximum quantum yield of PSII, Fv/Fm, did not change with either drought in the field or water or salinity stress in the glasshouse. Nevertheless, WD and SI treatments caused a decrease in the photochemical (qP) and an increase in the non-photochemical (qN) quenching coefficients relative to controls; qN was unaffected by the SS treatment. The occurrence of co-limitation of A by stomatal and non-stomatal factors in plants of L. nodosum may be associated with the extended leaf duration under water or saline stress. Additionally, osmotic adjustment may partly explain the relative maintenance of A and gs in the SS and SI treatments and the tolerance to salinity of plants of this species in coastal habitats.

Disasters↗
PubMed2000

Worster-Drought syndrome, a mild tetraplegic perisylvian cerebral palsy. Review of 47 cases.

A retrospective case-note analysis was undertaken of 47 children with a congenital upper motor neurone bulbar palsy (excluding pure speech dyspraxia) to clarify the phenotype of Worster-Drought syndrome (WDS) and to record its associated features and complications. The results revealed that the study children had significant bulbar problems (with 80% still needing a modified diet and a similar number using augmentative communication methods at last review). There were also high rates of predictable bulbar complications (86% had dribbling, 60% had glue ear, gastro-oesophageal reflux in 40%, history of poor nutrition in 40% and aspiration in 40%). Most of the children had additional complex impairments (91% had mild pyramidal tetraplegia, 81% learning difficulties, 60% congenital defects, 41% neuropsychiatric problems and 28% epilepsy). Over half of the children had significant medical problems in the first year, but mean age at diagnosis was 6 years. There were no obvious causes in pregnancy or birth. Six children had a family history of WDS and 32% (12/37) had abnormal neuroimaging including five with bilateral perisylvian polymicrogyria. In our experience, WDS is not uncommon, is relatively easily diagnosed and is crucial not to miss as the management of these children's multiple impairments is complex and requires a careful team approach. WDS falls clearly within the cerebral palsies as a syndrome that includes motor impairment arising from static damage to the brain in early life. The common presence of cognitive, behavioural and seizure impairments strongly supports the cerebral cortical (presumably perisylvian) localization. Its core elements are a suprabulbar paresis, a mild spastic tetraplegia and a significant excess of cognitive and behavioural impairments and epilepsy. The complete overlap in phenotype between WDS and the bilateral perisylvian syndrome leads us to propose that they are the same condition. WDS is startlingly absent from epidemiological studies of the cerebral palsies and rarely diagnosed, presumably because of lack of clinical awareness of the condition and lack of major gross motor impairments.

Adolescent↗
PubMed2001

The long-distance abscisic acid signal in the droughted plant: the fate of the hormone on its way from root to shoot.

Abscisic acid (ABA) is a potent molecule that certainly modifies stomatal behaviour and plant water loss and probably acts to modify the growth of leaves. The hormone is synthesized both in the leaves and the roots of the plant and in the soil and may move freely from plant to soil and soil to plant. It can also move rapidly through the plant in both the xylem and the phloem and will partition between different compartments in different tissues largely as a function of pH. It is described here how perturbations in soil conditions around the roots and the water status of the air can modify the fluxes of ABA around the plant and its accumulation in different compartments and different tissues. These fluxes can be interpreted as signals of different stresses imposed on the plant and consideration is given to how different perturbations can exert subtle changes which are manifest as modified shoot growth rates and functioning. Most emphasis in the discussion is placed upon the plant's responses to the imposition of soil and atmospheric drought.

Abscisic Acid↗
PubMed2026

The R2R3-MYB transcription factor ScMYB20 negatively regulates drought and salt tolerance through a dual-repression of ScCHALCONE SYNTHASE-1 (ScCHS1)-mediated flavonoid biosynthesis in the desert moss Syntrichia caninervis.

The desert moss Syntrichia caninervis is one of the most desiccation-tolerant land plants known and provides a powerful system for dissecting the molecular foundations of extreme stress adaptation in early-diverging land lineages. The MYB transcription factor superfamily orchestrates secondary metabolism and stress signaling across plants, yet its lineage-specific evolution and mechanistic deployment in bryophytes remain poorly understood. Here, we identified 65 ScMYB genes in the S. caninervis genome and showed that the family expanded predominantly through dispersed duplication, with no detectable synteny to vascular-plant MYBs, indicating bryophyte-specific neo-functionalization. Integrating phylogenetic clustering, cis-element architecture and stress-responsive expression profiling, we pinpointed ScMYB20, a nuclear-localized, S13-subgroup R2R3-MYB that is rapidly and strongly induced by dehydration and salinity. Heterologous overexpression in Arabidopsis, together with overexpression and RNAi in S. caninervis, demonstrated that ScMYB20 negatively regulates drought and salt tolerance by suppressing antioxidant capacity, osmotic adjustment and photosynthetic performance, while concomitantly elevating ROS and MDA accumulation. Mechanistically, ScMYB20 directly binds a TAACCA motif in the ScCHS1 promoter to repress its transcription, and simultaneously sequesters the WD40 protein ScTTG1, a positive transcriptional activator of ScCHS1, thereby antagonising ScTTG1-mediated activation. Transient ScCHS1 overexpression restored flavonoid accumulation, antioxidant capacity and stress tolerance. Together, our findings define a dual-repression module (ScMYB20-ScTTG1-ScCHS1) that fine-tunes flavonoid flux under abiotic stress, and provide evolutionary and mechanistic insights into how R2R3-MYB repressors evolved to balance metabolic investment and stress survival in land plants.

Syntrichia caninervis↗
PubMed2006

Arabidopsis and tobacco plants ectopically expressing the soybean antiquitin-like ALDH7 gene display enhanced tolerance to drought, salinity, and oxidative stress.

Despite extensive studies in eukaryotic aldehyde dehydrogenases, functional information about the ALDH7 antiquitin-like proteins is lacking. A soybean antiquitin homologue gene, designated GmTP55, has been isolated which encodes a dehydrogenase motif-containing 55 kDa protein induced by dehydration and salt stress. GmTP55 is closely related to the stress-induced plant antiquitin-like proteins that belong to the ALDH7 family. Transgenic tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana) plants constitutively expressing GmTP55 have been obtained in order to examine the physiological role of this enzyme under a variety of stress conditions. Ectopic expression of GmTP55 in both Arabidopsis and tobacco conferred tolerance to salinity during germination and to water deficit during plant growth. Under salt stress, the germination efficiency of both transgenic tobacco and Arabidopsis seeds was significantly higher than that of their control counterparts. Likewise, under progressive drought, the transgenic tobacco lines apparently kept the shoot turgidity to a normal level, which contrasted with the leaf wilt phenotype of control plants. The transgenic plants also exhibited an enhanced tolerance to H(2)O(2)- and paraquat-induced oxidative stress. Both GmTP55-expressing Arabidopsis and tobacco seeds germinated efficiently in medium supplemented with H(2)O(2), whereas the germination of control seeds was drastically impaired. Similarly, transgenic tobacco leaf discs treated with paraquat displayed a significant reduction in the necrotic lesions as compared with control leaves. These transgenic lines also exhibited a lower concentration of lipid peroxidation-derived reactive aldehydes under oxidative stress. These results suggest that antiquitin may be involved in adaptive responses mediated by a physiologically relevant detoxification pathway in plants.

Aldehyde Dehydrogenase↗
PubMed2006

Monitoring plant and soil water status: established and novel methods revisited and their relevance to studies of drought tolerance.

In all studies of the effects of water deficits on plant functioning there is a need for an accurate and comprehensive definition of treatments and their effects on plant water status. The various measures of water status used in plant and soil science are reviewed and their appropriateness for different purposes such as for studies of mechanistic effects of water deficits on plants, for breeding of drought-tolerant plants, or for management of irrigation systems are reviewed. An important conclusion is that the frequent emphasis on water potential rather than on cell turgor can be shown to be misleading, as can be measurements in the leaf. The disadvantages of the current trend towards the omission of necessary water-status measurements, especially common in more molecular studies, are outlined, and recommendations made for minimal sets of measurements for specific types of experiments.

Agriculture↗
PubMed1999

Mapping of 25 drought-inducible genes, RD and ERD, in Arabidopsis thaliana.

We mapped 25 Arabidopsis thaliana drought-inducible genes. Responsive to Dehydration (RD) and Early Responsive to Dehydration (ERD), to the Arabidopsis genome and compared map positions with those of mutants that show environmental stress response. We hybridized CIC yeast artificial chromosome (YAC) library filters with the cDNAs and determined the map positions of 18 corresponding genes. We screened the P1 library with 7 other clones and analyzed segregation of their restriction fragment length polymorphisms (RFLP) in recombinant inbred (RI) lines. One cDNA could be mapped because it had been sequenced by the Arabidopsis genome sequencing program.

Adaptation, Biological↗
PubMed2001

MIP genes are down-regulated under drought stress in Nicotiana glauca.

Water flux across cell membranes has been shown to occur not only through the lipid bilayer, but also through aquaporins, which are members of the major intrinsic protein (MIP) super-family of channel proteins. Aquaporins greatly increase the membrane permeability for water, but may also be regulated, allowing cellular control over the rate of water influx/efflux. Water flux is crucial for stomatal opening and closing, but little is known about the role that aquaporins play in stomatal physiology. Our initial goal was to isolate and characterize the MIP genes expressed in guard cells of the model plant, Nicotiana glauca. Degenerate oligonucleotides corresponding to amino acid sequences conserved in tonoplast intrinsic proteins (TIPs) or plasma membrane intrinsic proteins (PIPs) were used to amplify portions of MIP genes by RT-PCR. These PCR products were used as probes in screening a N. glauca guard cell cDNA library. We isolated three clones (NgMIP1, NgMIP2 and NgMIP3) homologous to TIPs and two clones (NgMIP4 and NgMIP5) homologous to PIPs. All of the MIP genes we characterized displayed highest levels of mRNA accumulation in roots or stems, with lower levels of expression in mesophyll cells and whole leaves, and lowest transcript accumulation in guard cell RNA. Interestingly, the accumulation of transcripts arising from NgMIP2, NgMIP3 and NgMIP4 diminished dramatically in drought-stressed plants. This down-regulation of MIP gene expression may result in reduced membrane water permeability and may encourage cellular water conservation during periods of dehydration stress.

Adaptation, Physiological↗