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PubMedDate not supplied

Population growth, fertility, mortality and migration in drought prone areas in Ethiopia.

To assess the population dynamics of drought-prone communities, we investigated 605 households in the pastoralist Boran community of Dubluk and in the agricultural community of Elka, both located in southern Ethiopia. The age and sex composition of the population as well as records of births, deaths and patterns of migration were observed for 2 consecutive years. Repeated surveys of the same households revealed much higher rates for deaths and births than did cross-sectional surveys with a one-year recall period. Indirect mortality estimates showed that the under 5 years mortality rates (per 1000 births) were 135 in Dubluk and 219 in Elka. Highest crude death rates were observed in Elka during periods of meningitis and malaria epidemics. During the period of observation, death rates fluctuated to a greater extent than birth rates. Both communities had very high rates of natural increase: in Dubluk 39.0/1000 and in Elka 37.1/1000. In Dubluk, this rate was far higher than any previously recorded and may have indicated that fertility regulating mechanisms, traditionally inherent in the pastoralist social organization, had become weaker as part of cultural changes. Dubluk represented a semi-nomadic society with a moderately high mobility pattern. Peak periods of migration coincided with times of food scarcity in Elka.

Adolescent↗
PubMed2004

Potent hydroxyl radical-scavenging activity of drought-induced type-2 metallothionein in wild watermelon.

Wild watermelon (Citrullus lanatus sp.) has the ability to tolerate severe drought/high light stress conditions despite carrying out normal C3-type photosynthesis. Here, mRNA differential display was employed to isolate drought-responsive genes in the leaves of wild watermelon. One of the isolated genes, CLMT2, shared significant homology with type-2 metallothionein (MT) sequences from other plants. The second-order rate constant for the reaction between a recombinant CLMT2 protein and hydroxyl radicals was estimated to be 1.2 x 10(11) M(-1) s(-1), demonstrating that CLMT2 had an extraordinary high activity for detoxifying hydroxyl radicals. Moreover, hydroxyl radical-catalyzed degradation of watermelon genomic DNA was effectively suppressed by CLMT2 in vitro. This is the first demonstration of a plant MT with antioxidant properties. The results suggest that CLMT2 induction contributes to the survival of wild watermelon under severe drought/high light stress conditions.

Amino Acid Sequence↗
PubMed2005

A guard-cell-specific MYB transcription factor regulates stomatal movements and plant drought tolerance.

Stomatal pores located on the plant epidermis regulate CO(2) uptake for photosynthesis and the loss of water by transpiration. The opening and closing of the pore is mediated by turgor-driven volume changes of two surrounding guard cells. These highly specialized cells integrate internal signals and environmental stimuli to modulate stomatal aperture for plant survival under diverse conditions. Modulation of transcription and mRNA processing play important roles in controlling guard-cell activity, although the details of these levels of regulation remain mostly unknown. Here we report the characterization of AtMYB60, a R2R3-MYB gene of Arabidopsis, as the first transcription factor involved in the regulation of stomatal movements. AtMYB60 is specifically expressed in guard cells, and its expression is negatively modulated during drought. A null mutation in AtMYB60 results in the constitutive reduction of stomatal opening and in decreased wilting under water stress conditions. Transcript levels of a limited number of genes are altered in the mutant, and many of these genes are involved in the plant response to stress. Our data indicate that AtMYB60 is a transcriptional modulator of physiological responses in guard cells and open new possibilities to engineering stomatal activity to help plants survive desiccation.

Adaptation, Physiological↗
PubMed2005

Compensation processes of Aleppo pine (Pinus halepensis Mill.) to ozone exposure and drought stress.

A long-term experiment was performed to study the effects of O3 and drought-stress (DS) on Aleppo pine seedlings (Pinus halepensis Mill.) exposed in open-top chambers. Ozone reduced gas exchange rates, ribulose-1,5-biphosphate carboxylase/oxygenase activity (Rubisco), aboveground C and needle N concentrations and C/N ratio and Ca concentrations of the twigs under 3 mm (twigs<3) and the aerial biomass. Also it increased phosphoenolpyruvate carboxylase (PEPc) and N and K concentrations of the twigs<3. Water stress decreased gas exchange rates, predawn needle water potential (PsiPd), C/N ratio, twigs<3 Ca, plant growth, aerial biomass and increased N, twigs with a diameter above 3 mm P and Mg concentrations. The combined exposure to both stresses increased N concentrations of twigs<3 and roots and aboveground biomass K content and decreased root C, maximum daily assimilation rate and instantaneous water use efficiency. The sensitivity of Aleppo pine to both stresses is determined by plant internal resource allocation and compensation mechanisms to cope with stress.

Air Pollutants↗
PubMed2006

Constitutive expression of abiotic stress-inducible hot pepper CaXTH3, which encodes a xyloglucan endotransglucosylase/hydrolase homolog, improves drought and salt tolerance in transgenic Arabidopsis plants.

Xyloglucan endotransglucosylase/hydrolase (XTH) has been recognized as a cell wall-modifying enzyme, participating in the diverse physiological roles. From water-stressed hot pepper plants, we isolated three different cDNA clones (pCaXTH1, pCaXTH2, and pCaXTH3) that encode XTH homologs. RT-PCR analysis showed that three CaXTH mRNAs were concomitantly induced by a broad spectrum of abiotic stresses, including drought, high salinity and cold temperature, and in response to stress hormone ethylene, suggesting their role in the early events in the abiotic-related defense response. Transgenic Arabidopsis plants that constitutively expressed the CaXTH3 gene under the control of the CaMV 35S promoter exhibited abnormal leaf morphology; the transgenic leaves showed variable degrees of twisting and bending along the edges, resulting in a severely wrinkled leaf shape. Microscopic analysis showed that 35S-CaXTH3 leaves had increased numbers of small-sized cells, resulting in disordered, highly populated mesophyll cells in each dorsoventral layer, and appeared to contain a limited amount of starch. In addition, the 35S-CaXTH3 transgenic plants displayed markedly improved tolerance to severe water deficit, and to lesser extent to high salinity in comparison with the wild-type plants. These results indicate that CaXTH3 is functional in heterologous Arabidopsis cells, thereby effectively altering cell growth and also the response to abiotic stresses. Although the physiological function of CaXTHs is not yet clear, there are several possibilities for their involvement in a subset of physiological responses to counteract dehydration and high salinity stresses in transgenic Arabidopsis plants.

Amino Acid Sequence↗
PubMed2004

Photosynthetic response of transgenic soybean plants, containing an Arabidopsis P5CR gene, during heat and drought stress.

The biochemical basis of heat/drought tolerance was investigated by comparing the response of antisense and sense transgenic soybean plants (containing the L-delta1-pyrroline-5-carboxylate reductase gene) with non-transgenic wild-type plants. The plants were subjected to a simultaneous drought and heat stress of 2 days, whereafter they were rewatered at 25 degrees C. During this time the sense plants only showed mild symptoms of stress compared to the antisense plants which were severely stressed. Upon stress, nicotinamide adenine dinucleotide phosphate (NADP+) levels decreased in antisense while it increased in sense plants. Recovery with respect to NADP+ levels was best in sense plants. Sense plants had the highest ability to accumulate proline during stress and to metabolise proline after rewatering. Analyses of the fast phase chlorophyll-a fluorescence transients showed dissociation of the oxygen-evolving complex (OEC) upon stress in all plants tested. In the sense plants, which best resisted the stress, OEC dissociation was bypassed by proline feeding electrons into photosystem 2 (PSII), maintaining an acceptable nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) level, preventing further damage. Upon recovery, NADPH is consumed during oxidation of accumulated proline providing high Levels of NADP+ to act as electron acceptor to PSII, which indirectly may ameliorate the inhibition and/or the effect of uncoupling of the OEC.

Acclimatization↗
PubMed2005

Conservation of the drought-inducible DS2 genes and divergences from their ASR paralogues in solanaceous species.

The drought-inducible DS2 genes of potatoes are members of the ASR (abscisic acid, stress and ripening) gene family. Previously it was shown that expression of DS2 genes is highly dehydration-specific in potato leaves, is not inducible by cold, heat, salt, hypoxia or oxidative stresses, and is independent of abscisic acid (ABA). Now it is shown that StDS2 does not respond either to sucrose or any plant hormones. Conservation of DS2 genes with this unique mode of regulation was studied in the solanaceous species with different relationships to potatoes. DS2 orthologues were identified by DNA sequence alignment in the closely related Lycopersicon and Capsicum species but not in the more distantly related Nicotiana sp. DNA and RNA gel blot analysis revealed the presence of a gene highly homologous to the potato gene StDS2 in tomato (LeDS2) with the same desiccation-specific expression in leaves and organ-specific expression in flowers and green fruits. The LeDS2 promoter was isolated and found to be almost identical in sequence with the promoter of StDS2, except for a 45-bp insertion in tomato. In contrast, no gene highly similar to StDS2 was detected in Nicotiana species on DNA gel blots. Neither StDS2 nor LeDS2 promoter regions were able to confer expression for the beta-glucuronidase (GUS) reporter gene in transgenic tobacco plants indicating that the trans regulatory factors necessary for DS2 expression are not conserved either in Nicotiana tabacum. These data suggest a narrow species-specificity and late evolution of the DS2-type genes within the family Solanaceae.

Base Sequence↗
PubMed2005

Adaptation of photosynthesis in marama bean Tylosema esculentum (Burchell A. Schreiber) to a high temperature, high radiation, drought-prone environment.

Marama bean, Tylosema esculentum, is a tuberous legume native to the Kalahari region of Southern Africa where it grows under high temperatures (typical daily max 37 degrees C during growing season) and radiation (frequently in excess of 2000 micromol m(-2) s(-1)) in sandy soils with low rainfall. These conditions might be expected to select for increased water-use efficiency of photosynthesis. However, marama was found to give similar leaf photosynthetic rates to other C3 plants for a given internal leaf CO2 concentration and Rubisco content. Under conditions of increasing drought, no increase in water-use efficiency of photosynthesis was observed, but stomata closed early and preceded any change in leaf water potential. The possibility of subtle adaptations of photosynthetic characteristics to its natural environment were investigated at the level of Rubisco kinetics. The specificity factor of marama Rubisco was slightly lower than that of wheat, but the apparent Km for CO2 in air (Km') was about 20% lower than that of wheat. This is consistent with better adaptation for efficient photosynthesis at high temperatures in marama compared to wheat, although the net benefit is predicted to be very small (<0.5% at 35 degrees C). The sequence of marama rbcL gene shows 27 deduced amino acid residue differences from that for wheat, and the possibility that one or more of these cause the difference in Rubisco Km' is discussed.

Adaptation, Physiological↗
PubMed2006

A phosphatidylserine decarboxylase activity in root cells of oat (Avena sativa) is involved in altering membrane phospholipid composition during drought stress acclimation.

During acclimation to drought stress, the lipid composition of oat root cell membranes is altered. The level of phosphatidylethanolamine (PE), a non-bilayer forming lipid, is increased relative to the bilayer-forming lipid phosphatidylcholine (PC). These changes are believed to increase stress tolerance by increasing the flexibility of the membranes. To elucidate if de novo lipid synthesis is involved in altering membrane lipid composition, oat plants, acclimated or non-acclimated, were incubated in vivo with radioactively labelled lipid precursors. The labelling pattern indicated that de novo synthesis, at least partly, is causing the alterations. In plants, phospholipids can be synthesized by the Kennedy pathway, with addition of activated head groups to diacylglycerol (DAG) or, alternatively, via the CDP-DAG pathway, where phospahtidylserine (PS) is decarboxylated to form PE. To reveal the importance of the respective pathways during acclimation, we studied the effect of a decarboxylase inhibitor and the relative incorporation of [(3)H]-serine and [(14)C]-ethanolamine in vivo. Activities of CTP:ethanolaminephosphate cytidyltransferase (EC 2.7.7.14), phosphatidylserine decarboxylase (EC 4.1.1.65) and phosphatidylserine synthase; CDP-DAG:L-serine o-phosphatidyltransferase (EC 2.7.8.8) were measured and additionally, the presence of a PS decarboxylase (PSD1) in oat was confirmed by immunoblotting. The results suggest that PE synthesis via the Kennedy pathway is downregulated during acclimation and that synthesis by PS decarboxylation, via the CDP-DAG pathway, is increased, mainly through an increased activity of PS synthase.

Acclimatization↗
PubMed2005

Engineering drought and salinity tolerance in plants: lessons from genome-wide expression profiling in Arabidopsis.

World food security is increasingly dependent on continuous crop improvement and, in particular, the development of crops with increased drought and salinity tolerance. The completed genomic sequence of the model plant Arabidopsis thaliana and the development of whole-genome microarrays, together with increasing repositories of publicly available data and data analysis tools, have opened new avenues to genome-wide systemic analysis of plant stress responses. Here we outline examples of how this full-genome expression profiling can contribute to our understanding of complex stress responses and the identification and evaluation of novel transgenes that could hold the key to the development of commercially viable and sustainable crop plants.

Arabidopsis↗
PubMed2004

European starling chicks benefit from high yolk testosterone levels during a drought year.

Avian egg yolk contains androgenic hormones, such as testosterone, of maternal origin. Experimental elevation of yolk testosterone levels enhances growth of canary chicks. Success in sibling competition, due to increased begging, is presumed to underlie this growth enhancement, because canary hatchlings from testosterone-treated eggs beg longer in response to vibrational stimuli than controls. Furthermore, experimental elevation of both yolk androstenedione and testosterone increased chick growth and begging in black-headed gulls. We measured daily growth of European starling (Sturnus vulgaris) chicks hatching from testosterone-treated or vehicle-treated (control) eggs until 14 days of age, and measured begging behavior at hatching and at 5 days of age. A temporary drought caused relatively high levels of early brood reduction for this population; 2- and 3-day-old chicks were most likely to starve. We found that chicks from testosterone-treated eggs were less likely to starve than control chicks, and were heavier on the days when most brood reduction occurred. However, chicks from testosterone-treated eggs begged less than control chicks on the day of hatching, and begged similarly at 5 days of age. Thus, while yolk testosterone did increase growth during periods of (presumably) high competition, increased begging does not appear to mediate this effect. Instead, testosterone may induce more efficient energy use, for example, by decreasing ineffective begging. While our results indicate that elevated yolk testosterone enhances survival, and thus offspring and parental fitness, further evidence regarding the fitness consequences of yolk androgens are vital to understanding their role in avian life history.

Adaptation, Physiological↗
PubMed2001

Involvement of antioxidants and lipid peroxidation in the adaptation of two cool-season grasses to localized drought stress.

In natural environments, drought often occurs in surface soil while water is available for plant uptake deeper in the soil profile. The objective of the study was to examine the involvement of antioxidant metabolism and lipid peroxidation in the responses of two cool-season grasses to surface soil drying. Kentucky bluegrass (Poa pratensis L) and tall fescue (Festuca arundinacea Schreb.) were grown in split tubes, consisting of two sections (each 10 cm in diameter and 20 cm long). Grasses were subjected to three soil moisture regimes: (a) well-watered control: whole soil profile was watered; (b) surface drying: surface 20 cm of soil was dried by withholding irrigation and the lower 20 cm of soil was watered; (c) full drying: whole soil profile was dried. Surface drying had no effects on relative water content (RWC) and chlorophyll content (Chl) for both grasses and only slightly reduced shoot growth for tall fescue. Superoxide dismutase (SOD) activity increased, while catalase (CAT) and peroxidase (POD) activities remained unchanged during most periods of surface drying. Malondialdehyde (MDA) content was unaffected by surface drying for tall fescue, but increased initially and then decreased to the control level for Kentucky bluegrass. Under full drying, RWC, Chl content, and shoot dry weight decreased, but MDA content increased in both grasses; SOD and POD activities initially increased transiently and then decreased; CAT remained unchanged for 25 days and then decreased. These results suggested that both Kentucky bluegrass and tall fescue were capable of surviving surface soil drying. This capability could be related to increases in antioxidant activities, particularly SOD and CAT. However, full drying suppressed antioxidant activities and induced lipid peroxidation.

Journal Article↗
PubMed2002

Potential sensitivity of mires to drought, acidification and mobilisation of heavy metals: the sediment s/(Ca + Mg) ratio as diagnostic tool.

In recent decades sulphate concentrations in the ground water in many parts of The Netherlands have increased dramatically resulting in increased production of iron-(di)sulphides in sediments of ecosystems fed by this water. A sediment survey was carried out to study the potential sensitivity of wetlands to drought and subsequent acidification as a consequence of iron-(di)sulphide oxidation. Dessication led to severe acidification and mobilisation of heavy metals when the sediment S/(Ca + Mg) ratio exceeded 2/ 3. A total of 47% of the investigated locations contained S/(Ca + Mg) ratios higher than 2/3 and in 100, 75 and 50% of the locations mobilisation of Zn, Cd and Ni exceeded the Dutch signal value for ground water. Consistent with the sediment survey, lime addition experiments confirmed that increasing the buffer capacity, down to a S/(Ca + Mg) ratio 2/3, led to a drastic inhibition of the acidification and heavy metal percolation from dredged sediments. The performance of the same processes under drained field conditions demonstrates the relevance of these processes during dry summers.

Cadmium↗
PubMed2001

Drought and flock isolation may enhance the development of anthelmintic resistance in nematodes.

A survey of anthelmintic resistant nematodes was conducted in sheep and goat flocks in Greece using in vivo and in vitro tests. Faecal egg count reduction tests in Macedonia were all greater than 99% indicating very high sensitivity of the nematodes to anthelmintics. In vitro tests showed benzimidazole resistant Teladorsagia circumcincta in 17 out of 106 flocks on small islands. On the mainland there were only three cases of benzimidazole resistance out of 310 flocks and animals had recently been introduced to the flocks. Flocks on the islands are isolated and there are higher temperatures than on the more mountainous mainland, where flocks tend to intermingle. It is concluded that drought and isolation are likely to be the major factors accounting for the development of anthelmintic resistance in nematodes in the island flocks.

Animal Husbandry↗
PubMed2001

Worster-Drought and congenital perisylvian syndromes-a continuum?

A 5-year-old female was evaluated because of severe speech and expressive language delay. On examination, she could hardly speak and communicated through gestures. She manifested severe dysarthria and difficulty in protruding and moving her tongue laterally. She lacked coordination of the swallowing process, with drooling and an increased mental reflex. Her cognitive development was normal, and no associated neurologic dysfunction of the limbs was noted. On follow-up, the child experienced two episodes of seizures at 6 years of age. Magnetic resonance imaging of the brain demonstrated perisylvian and frontal polymicrogyria. Clinical and radiologic findings demonstrated a similarity and continuum between congenital suprabulbar paresis (Worster-Drought syndrome) and perisylvian syndrome.

Bulbar Palsy, Progressive↗
PubMed2003

Molecular responses to drought, salinity and frost: common and different paths for plant protection.

Drought, high salinity and low temperature are major environmental factors that limit plant productivity. Plants respond and adapt to these stresses in order to survive. Signaling pathways are induced in response to environmental stress and recent molecular and genetic studies have revealed that these pathways involve many components. In this review, we highlight recent findings on the gene expression associated with stress responses and the signaling pathways that are either common or specific to the response.

Adaptation, Physiological↗
PubMed1996

Molecular responses to drought and cold stress.

A variety of plant genes are induced by drought and cold stress, and they are thought to be involved in the stress tolerance of the plant. At least five signal transduction pathways control these genes: two are dependent on abscisic acid (ABA), and the others are ABA-independent. A novel cis-acting element involved in one of the ABA-independent signal transduction pathways has been identified. In addition, a number of genes for protein kinases and transcription factors thought to be involved in the stress signal transduction cascades have been shown to be induced by environmental stresses.

Abscisic Acid↗
PubMedDate not supplied

Plant physiology: spreading a drought warning.

Communication between the root and the shoot forms a central part of the coordinated response of plants to drought. Recent evidence suggests that a K+ channel expressed in the stelar tissue of the root may have a major role in this process.

Adaptation, Physiological↗