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At least 1,153 records · Page 64Linked to original sources
PubMed2000

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat.

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE(i)) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material (delta(p)) is increased by the increase of drought intensity. The delta(p) at a given level of C(i)/C(a) is reduced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE(t)) is negatively correlated with Delta in both nitrogen supply treatments and increased with the nitrogen supply.

Journal Article↗
PubMed2003

New variant famine: AIDS and food crisis in southern Africa.

Southern Africa is undergoing a food crisis of surprising scale and novelty. The familiar culprits of drought and mismanagement of national strategies are implicated. However, this crisis is distinct from conventional drought-induced food shortages with respect to those vulnerable to starvation, and the course of impoverishment and recovery. We propose that these new aspects to the food crisis can be attributed largely to the HIV/AIDS epidemic in the region. We present evidence that we are facing a new variant famine. We have used frameworks drawn from famine theory to examine the implications. HIV/AIDS has created a new category of highly vulnerable households--namely, those with ill adults or those whose adults have died. The general burden of care in both AIDS-affected and non-AIDS-affected households has reduced the viability of farming livelihoods. The sensitivity of rural communities to external shocks such as drought has increased, and their resilience has declined. The prospects for a sharp decline into severe famine are increased, and possibilities for recovery reduced.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Plant resistance to environmental stress

A common effect of many environmental stresses is to cause oxidative damage; consequently, the antioxidant system is being intensively investigated. The use of transgenic plants to probe the role of the antioxidant system continues to be an important approach. The uncharted area of signal transduction in relation to oxidative stress is beginning to attract attention. Studies of drought response at the cellular level have focused on the role of compatible solutes (osmolytes) in acclimation to water stress. Information on signal transduction processes during drought is beginning to appear. As with the antioxidant system, there is increasing use of metabolic engineering in transgenic plants to introduce exotic compatible solutes. It is concluded that these potentially have a use in understanding, or even improving, drought resistance; however, there is a need for the assessment of stress tolerance of transgenics to be carried out at a more sophisticated level and for a critical analysis of the relevance for crop yield of the genes currently being manipulated.

Journal Article↗
PubMed2003

Comparison of growth and performance in upland and lowland switchgrass types to water and nitrogen stress.

The objective of the study was to examine lowland (Alamo and Kanlow) and upland (Blackwell and Caddo) cultivars of switchgrass (Panicum virgatum L.) for differences in response to water deficit and nitrogen fertilizer. Cultivars were grown in pots with fritted clay at two water levels: well watered and deficit conditions (-0.1 and -1.0 MPa) and two nitrogen levels (10 and 100 kg ha(-1)). Nitrogen determined growth potential of the cultivars more than water availability. The lowland cultivars produced greater biomass yields than upland cultivars. However, upland cultivars showed a smaller response to drought stress. Under water stress conditions all cultivars exhibited a higher leaf percentage of total dry matter (DM), with the upland cultivars having the highest leaf percentage of total DM. Nitrogen proved to have more of an effect on single-leaf photosynthesis rates than water. Alamo demonstrated the greatest biomass production among all cultivars. The differences found between the two lowland cultivars suggest that Alamo would be better suited for forage and biomass production in central Texas, being a higher producer under drought and non-drought conditions than Kanlow as well as upland cultivars.

Geography↗
PubMed2001

Modulation of abscisic acid signal transduction and biosynthesis by an Sm-like protein in Arabidopsis.

The phytohormone abscisic acid (ABA) regulates plant growth and development as well as stress tolerance. The Arabidopsis sad1 (supersensitive to ABA and drought) mutation increases plant sensitivity to drought stress and ABA in seed germination, root growth, and the expression of some stress-responsive genes. sad1 plants are also defective in the positive feedback regulation of ABA biosynthesis genes by ABA and are impaired in drought stress induction of ABA biosynthesis. SAD1 encodes a polypeptide similar to multifunctional Sm-like snRNP proteins that are required for mRNA splicing, export, and degradation. These results suggest a critical role for mRNA metabolism in the control of ABA signaling as well as in the regulation of ABA homeostasis.

Abscisic Acid↗
PubMed1988

Epidemic cholera in Mali: high mortality and multiple routes of transmission in a famine area.

During the 1984 cholera epidemic in Mali, 1793 cases and 406 deaths were reported, a death-to-case ratio of 23%. In four affected villages, the mean clinical attack rate was 1.5 and 29% of affected persons died. In 66% of cases the illness began more than 48 h after the village outbreak began, when supplies from outside the village were potentially available. Deaths occurred because patients failed to seek care or received only limited rehydration therapy when they did. Case-control studies identified two routes of transmission: drinking water from one well in a village outside the drought area, and eating left-over millet gruel in a drought-affected village. Drought-related scarcity of curdled milk may permit millet gruel to be a vehicle for cholera. Cholera mortality in the Sahel could be greatly reduced by rapid intervention in affected villages, wide distribution of effective rehydration materials, and educating the population to seek treatment quickly.

Adolescent↗
PubMed2003

Cause-effect relationships in analytical surveys: an illustration of statistical issues.

Establishing cause-effect is critical in the field of natural resources where one may want to know the impact of management practices, wildfires, drought, etc. on water quality and quantity, wildlife, growth and survival of desirable trees for timber production, etc. Yet, key obstacles exist when trying to establish cause-effect in such contexts. Issues involved with identifying a causal hypothesis, and conditions needed to estimate a causal effect or to establish cause-effect are considered. Ideally one conducts an experiment and follows with a survey, or vice versa. In an experiment, the population of inference may be quite limited and in surveys, the probability distribution of treatment assignments is generally unknown and, if not accounted for, can cause serious errors when estimating causal effects. The latter is illustrated in simulation experiments of artificially generated forest populations using annual plot mortality as the response, drought as the cause, and age as a covariate that is correlated with mortality. We also consider the role of a vague unobservable covariate such as 'drought susceptibility'. Recommendations are made designed to maximize the possibility of identifying cause-effect relationships in large-scale natural resources surveys.

Animals↗
PubMed2003

Induction of a Crassulacean acid like metabolism in the C(4) succulent plant, Portulaca oleracea L.: physiological and morphological changes are accompanied by specific modifications in phosphoenolpyruvate carboxylase.

The induction of a Crassulacean acid like metabolism (CAM) was evidenced after 21-23 days of drought stress in the C(4) succulent plant Portulaca oleracea L. by changes in the CO(2) exchange pattern, in malic acid content and in titratable acidity during the day-night cycle. Light microscopy studies also revealed differences in the leaf structure after the drought treatment. Following the induction of the CAM-like metabolism, the regulatory properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), the enzyme responsible for the diurnal fixation of CO(2) in C(4) plants but nocturnal in CAM plants, were studied. The enzyme from stressed plants showed different kinetic properties with respect to controls, notably its lack of cooperativity, higher sensitivity to L-malate inhibition, higher PEP affinity and lower enzyme content on a protein basis. In both conditions, PEPC's subunit mass was 110 kDa, although changes in the isoelectric point and electrophoretic mobility of the native enzyme were observed. In vivo phosphorylation and native isoelectrofocusing studies indicated variations in the phosphorylation status of the enzyme of samples collected during the night and day, which was clearly different for the control and stressed groups of plants. The results presented suggest that PEPC activity and regulation are modified upon drought stress treatment in a way that allows P. oleracea to perform a CAM-like metabolism.

Journal Article↗
PubMed2004

The effect of exogenous jasmonic acid on induced resistance and productivity in amaranth (Amaranthus hypochondriacus) is influenced by environmental conditions.

Amaranthus hypochondriacus is a C4 pseudocereal crop capable of producing reasonable grain yields in adverse environmental conditions that limit cereal performance. It accumulates trypsin inhibitors and alpha-amylase inhibitors in seeds and leaves that are considered to act as insect feeding deterrents. Foliar trypsin and alpha-amylase inhibitors also accumulate by treatment with exogenous jasmonic acid (JA) in controlled laboratory conditions. Three field experiments were performed in successive years to test if two nonphytotoxic dosages of JA were capable of inducing inhibitor activity in A. hypochondriacus in agronomical settings, and if this induced response reduced insect herbivory and insect abundance in foliage and seed heads. The performance of JA-treated plants was compared to insecticide-treated plants and untreated controls. The effect of exogenous JA on the foliar levels of six additional putatively defence proteins was also evaluated. Possible adverse effects of JA induction on productivity were evaluated by measuring grain yield, seed protein content, and germination efficiency. The results present a complex pattern and were not consistent from year to year. To some extent, the yearly variability observed could have been consequence of growth under drought versus nondrought conditions. In a drought year, JA-treated plants had lower levels of insect herbivory-derived damage in apical leaves and panicle than control plants, whereas in nondrought years, there was an inconsistent effect on aphids, with no effect on lepidopteran larvae. JA treatments reduced the size of the insect community in seed heads. The effect varied with year. Exogenous JA did not adversely affect productivity, and in the absence of drought stress, the higher dosage enhanced grain yield. Induction of defensive proteins by JA, although sporadic, was more effective in nondrought conditions. The patterns of foliar protein accumulation observed suggest that they may be part of a constitutive, rather than inducible, chemical defense mechanism that is developmentally regulated and critically dependent on the environment. The results emphasize the difficulties that are often encountered when evaluating the performance of chemical elicitors of induced resistance in field settings.

Amaranthus↗
PubMed2001

Response to mild water stress in transgenic Pssu-ipt tobacco.

The response of antioxidant enzymes to cyclic drought was studied in control non-transformed tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) and two types of transgenic Pssu-ipt tobacco (grafted on wild rootstock and poorly rooted progeny of F1 generation) grown under different conditions of irradiation (greenhouse, referred as high light, versus growth chamber, referred as low light). Water stress cycles started with plants at two contrasting developmental stages, i.e., at the stage of vegetative growth (young) and at the onset of flowering (old). Drought reduced the growth of SR1 plants compared with transgenic ones, particularly, when treatment started in earlier stage of plant development. Relative leaf water content was significantly lower (below 70%) in all transgenic grafts and plants compared with the wild type, irrespective of age, drought, and growth conditions. The response of antioxidant enzymes was significantly dependent on plant type and plant age; nevertheless, growth conditions and water stress also affected enzyme activities. Contrary to non-transgenic tobacco, where about half of glutathione reductase activity was found in older plants, both transgenic types exhibited unchanged activities throughout plant development and stress treatment. No differences were found in catalase activity, although the growth in the greenhouse caused a moderate increase in all older plants. In contrast to non-transgenic and Pssu-ipt rooted plants, peroxidase activities (ascorbate, guaiacol, and syringaldazine peroxidase) in older Pssu-ipt grafts were up to four times higher, irrespective of growth and stress, nevertheless, the effect seemed to be age-dependent. Superoxide dismutase (SOD) activity was affected particularly by plant age but also by growth conditions. Unlike in older plants, water stress caused an increase of SOD activities in all younger plants. The differences observed in activities of enzymes of intermediary metabolism (i.e., malic enzyme and glucose-6-phosphate dehydrogenase) revealed that transgenic grafts probably compensated differently for a decrease of ATP and NADPH than control and transgenic rooted plants under stress.

Journal Article↗
PubMed1996

The Arabidopsis homeobox gene ATHB-7 is induced by water deficit and by abscisic acid.

Homeodomain-leucine zipper (HD-Zip) proteins are putative transcription factors encoded by a class of recently discovered homeobox genes as yet found only in plants. This paper reports on the characterization of one of these genes, ATHB-7, in Arabidopsis thaliana. ATHB-7 transcripts were present in all organs of the plant at low levels, but expression was induced several-fold by water deficit, osmotic stress as well as by exogenous treatment with abscisic acid (ABA), a response being detectable at 10(-8) M and reaching a maximum at 10(-6) M ABA. The ATHB-7 transcript was detected within 30 min after treatment with ABA and the transcript level was rapidly reduced after removal of the hormone. The induction of ATHB-7 was shown to be mediated strictly via ABA, since no induction of ATHB-7 was detectable in the ABA-deficient mutant aba-3 subjected to drought treatment. Induction levels in two ABA-insensitive mutants abi2 and abi3 were similar to the wild-type response. In the abi1 mutant, however, induction was impaired as 100-fold higher concentrations of ABA were required for a maximum induction as compared with wild-type. In this mutant the ATHB-7 response was reduced also after drought and osmotic stress treatments. These results indicate that ATHB-7 is transcriptionally regulated in an ABA-dependent manner and may act in a signal transduction pathway which mediates a drought response and also includes ABI1.

Abscisic Acid↗
PubMed2001

Antisense inhibition of protein phosphatase 2C accelerates cold acclimation in Arabidopsis thaliana.

Two related protein phosphatases 2C, ABI1 and AtPP2CA have been implicated as negative regulators of ABA signalling. In this study we characterized the role of AtPP2CA in cold acclimation. The pattern of expression of AtPP2CA and ABI1 was studied in different tissues and in response to abiotic stresses. The expression of both AtPP2CA and ABI1 was induced by low temperature, drought, high salt and ABA. The cold and drought-induced expression of these genes was ABA-dependent, but divergent in various ABA signalling mutants. In addition, the two PP2C genes exhibited differences in their tissue-specific expression as well as in temporal induction in response to low temperature. To elucidate the function of AtPP2CA in cold acclimation further, the corresponding gene was silenced by antisense inhibition. Transgenic antisense plants exhibited clearly accelerated development of freezing tolerance. Both exposure to low temperature and application of ABA resulted in enhanced freezing tolerance in antisense plants. These plants displayed increased sensitivity to ABA both during development of frost tolerance and during seed germination, but not in their drought responses. Furthermore, the expression of cold-and ABA-induced genes was enhanced in transgenic antisense plants. Our results suggest that AtPP2CA is a negative regulator of ABA responses during cold acclimation.

Abscisic Acid↗
PubMed2003

The sfr6 mutant of Arabidopsis is defective in transcriptional activation via CBF/DREB1 and DREB2 and shows sensitivity to osmotic stress.

The sfr6 mutant of Arabidopsis displays a deficit in freezing tolerance after cold acclimation. We previously observed that the transcripts of three cold-, ABA- and drought-inducible genes, each having a C-repeat motif or the drought-responsive element (CRT/DRE) in its promoter, failed to normally accumulate in this mutant. We now report that the effects of sfr6 upon transcript levels are reflected in the levels of the encoded proteins, confirming that the cold-inducible protein expression is affected by the sfr6 mutation. Using microarray analysis, we found not only that this effect may be general to cold-inducible genes with CRT/DRE promoter elements, but also that it extends to some other genes whose promoters lack a CRT/DRE element. The role of the CRT/DRE has been empirically tested by use of a synthetic promoter, confirming that the CRT/DRE is sufficient to confer the sfr6 effect upon expression. Tolerance of osmotic stress was also found to be reduced in sfr6, consistent with a role in osmotic stress tolerance for the cold-, ABA- and drought-inducible genes whose expression is affected by the sfr6 mutation.

Abscisic Acid↗
PubMed2001

Physical stress and diversity-productivity relationships: the role of positive interactions.

If environmental stress provides conditions under which positive relationships between plant species richness and productivity become apparent, then species that seem functionally redundant under constant conditions may add to community functioning under variable conditions. Using naturally co-occurring mosses and liverworts, we constructed bryophyte communities to test relationships between species diversity (1, 2, 4, 8, 16, 24, or 32 species) and productivity under constant conditions and when exposed to experimental drought. We found no relationship between species richness and biomass under constant conditions. However, when communities were exposed to experimental drought, biomass increased with species richness. Responses of individual species demonstrated that facilitative interactions rather than sampling effects or niche complementarity best explained results-survivorship increased for almost all species, and those species least resistant to drought in monoculture had the greatest increase in biomass. Positive interactions may be an important but previously underemphasized mechanism linking high diversity to high productivity under stressful environmental conditions.

Biomass↗
PubMed1986

Rapid evolution of a life history trait.

The copepod Diaptomus sanguineus begins diapause in permanent ponds in late March as an adaptation to avoid summer fish predation. During a study of copepod populations in two Rhode Island ponds, a severe drought dried one pond killing all fish. The second (control) pond did not dry, and no fish were killed. Before the drought copepods in the two ponds entered diapause on nearly the same date. After the drought, the timing of diapause shifted to later in the year in the pond that had lost its fish, while no shift occurred in the control pond. The direction of this shift in the onset of diapause is that expected had the copepods been released from natural selection for early spring diapause imposed by summer fish predation.

Journal Article↗
PubMed2005

Differential impact of environmental stresses on the pea mitochondrial proteome.

Exposure to adverse environmental conditions causes oxidative stress in many organisms, leading either to disease and debilitation or to response and tolerance. Mitochondria are a key site of oxidative stress and of cellular response and play important roles in cell survival. We analyzed the response of mitochondria in pea (Pisum sativum) plants to the common stresses associated with drought, cold, and herbicides. These treatments all altered photosynthetic and respiratory rates of pea leaves to various extents, but only herbicides significantly increased lipid peroxidation product accumulation. Mitochondria isolated from the stressed pea plants maintained their electron transport chain activity, but changes were evident in the abundance of uncoupling proteins, non-phosphorylating respiratory pathways, and oxidative modification of lipoic acid moieties on mitochondrial proteins. These data suggest that herbicide treatment placed a severe oxidative stress on mitochondria, whereas chilling and particularly drought were milder stresses. Detailed analysis of the soluble proteome of mitochondria by gel electrophoresis and mass spectrometry revealed differential degradation of key matrix enzymes during treatments with chilling being significantly more damaging than drought. Differential induction of heat shock proteins and specific losses of other proteins illustrated the diversity of response to these stresses at the protein level. Cross-species matching was required for mass spectrometry identification of nine proteins because only a limited number of pea cDNAs have been sequenced, and the full pea genome is not available. Blue-native separation of intact respiratory chain complexes revealed little if any change in response to environmental stresses. Together these data suggest that although many of the molecular events identified by chemical stresses of mitochondria from a range of model eukaryotes are also apparent during environmental stress of plants, their extent and significance can vary substantially.

Cold Temperature↗
PubMed2003

Photosynthetic flexibility in Pedilanthus tithymaloides poit, a CAM plant.

The induction of CAM in Pedilanthus tithymaloides (Euphorbiaceae) under water-limited conditions was evaluated by following diurnal oscillations of CO2 fixation, titratable acidity and malic acid content in the leaf extracts. CAM induction was assessed by measuring the activities of phosphoenolpyruvate carboxylase (PEPC), NADH-malate dehydrogenase (MDH) and phosphoenolpyruvate caroxykinase (PEPCK) in the leaves as well. Drought resulted in large increases in the nocturnal acid accumulation and rates of CO2 uptake in the leaves of P. tithymaloides. The drought-induced CAM activity tended to be reversible after re-watering. Nevertheless, under well-watered conditions, plants of P. tithymaloides showed day time CO2 uptake patterns with less pronounced diurnal oscillations of organic acids. Our data indicate that although P. tithymaloides is a CAM plant, environmental variables like drought induce photosynthetic flexibility in this species. This type of plasticity in CAM and metabolic versatility in P. tithymaloides should be an adaptation for prolonged survival under natural adverse edaphic and microclimate situations.

Carbon Dioxide↗
PubMed1987

Famine in Ethiopia 1983-1985: kwashiorkor and marasmus in four regions.

Parts of southern Ethiopia were form 1983 to 1985 affected by drought and famine. This study describes the prevalence of marasmus and kwashiorkor in four drought-affected regions: Bale, Sidamo, Gamu Gofa and southern Shoa. An analysis of 37,511 children in the 1-5 year age group representing 212 communities has been performed. The study demonstrates that both marasmus and kwashiorkor are facets of drought. The epidemiologies of kwashiorkor and marasmus differ: marasmus is the most common form of acute malnutrition in all areas, while kwashiorkor is found in a limited number of communities only. These latter communities have a subsistence farming economy, most often in ensete-growing areas. In the lowland semi-arid regions, which have an agro-pastoralist economy, kwashiorkor is virtually absent. These epidemiological findings are discussed in relation to different theories of the aetiology and pathogenesis of kwashiorkor.

Body Height↗