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PubMed2002

Drought- and desiccation-induced modulation of gene expression in plants.

Desiccation is the extreme form of dehydration. Tolerance of desiccation is acquired by seeds and in resurrection plants, a small group of angiosperms. Desiccation tolerance is the result of a complex cascade of molecular events, which can be divided into signal perception, signal transduction, gene activation and biochemical alterations leading to acquisition of tolerance. Many of these molecular processes are also observed during the dehydration of non-tolerant plants. Here we try to give an overview of the gene expression programmes that are triggered by dehydration, with particular reference to protective molecules and the regulation of their expression. Potential transgenic approaches to manipulating stress tolerance are discussed.

Journal Article↗
PubMed2000

A novel aldose/aldehyde reductase protects transgenic plants against lipid peroxidation under chemical and drought stresses.

Rapid accumulation of toxic products from reactions of reactive oxygen species (ROS) with lipids and proteins significantly contributes to the damage of crop plants under biotic and abiotic stresses. Here we have identified a stress-activated alfalfa gene encoding a novel plant NADPH-dependent aldose/aldehyde reductase that also exhibited characteristics of the homologous human enzyme. The recombinant alfalfa enzyme is active on 4-hydroxynon-2-enal, a known cytotoxic lipid peroxide degradation product. Ectopic synthesis of this enzyme in transgenic tobacco plants provided considerable tolerance against oxidative damage caused by paraquat and heavy metal treatment. These transformants could also resist a long period of water deficiency and exhibited improved recovery after rehydration. We found a reduced production of lipid peroxidation-derived reactive aldehydes in these transformed plants under different stresses. These studies reveal a new and efficient detoxification pathway in plants.

Adaptation, Physiological↗
PubMed2005

Simulation of Sahel drought in the 20th and 21st centuries.

The Sahel, the transition zone between the Saharan desert and the rainforests of Central Africa and the Guinean Coast, experienced a severe drying trend from the 1950s to the 1980s, from which there has been partial recovery. Continuation of either the drying trend or the more recent ameliorating trend would have far-ranging implications for the economy and ecology of the region. Coupled atmosphere/ocean climate models being used to simulate the future climate have had difficulty simulating Sahel rainfall variations comparable to those observed, thus calling into question their ability to predict future climate change in this region. We describe simulations using a new global climate model that capture several aspects of the 20th century rainfall record in the Sahel. An ensemble mean over eight realizations shows a drying trend in the second half of the century of nearly half of the observed amplitude. Individual realizations can be found that display striking similarity to the observed time series and drying pattern, consistent with the hypothesis that the observations are a superposition of an externally forced trend and internal variability. The drying trend in the ensemble mean of the model simulations is attributable to anthropogenic forcing, partly to an increase in aerosol loading and partly to an increase in greenhouse gases. The model projects a drier Sahel in the future, due primarily to increasing greenhouse gases.

Africa↗
PubMed1990

Molecular cloning of a plant betaine-aldehyde dehydrogenase, an enzyme implicated in adaptation to salinity and drought.

Many plants, as well as other organisms, accumulate betaine (N,N,N-trimethylglycine) as a nontoxic or protective osmolyte under saline or dry conditions. In plants, the last step in betaine synthesis is catalyzed by betaine-aldehyde dehydrogenase (BADH, EC 1.2.1.8), a nuclear-encoded chloroplastic enzyme. A cDNA clone for BADH (1812 base pairs) was selected from a lambda gt10 cDNA library derived from leaves of salt-stressed spinach (Spinacia oleracea L.). The library was screened with oligonucleotide probes corresponding to amino acid sequences of two peptides prepared from purified BADH. The authenticity of the clone was confirmed by nucleotide sequence analysis; this analysis demonstrated the presence of a 1491-base-pair open reading frame that contained sequences encoding 12 peptide fragments of BADH. The clone hybridized to a 1.9-kilobase mRNA from spinach leaves; this mRNA was more abundant in salt-stressed plants, consistent with the known salt induction of BADH activity. The amino acid sequence deduced from the BADH cDNA sequence showed substantial similarities to those for nonspecific aldehyde dehydrogenases (EC 1.2.1.3 and EC 1.2.1.5) from several sources, including absolute conservation of a decapeptide in the probable active site. Comparison of deduced and determined amino acid sequences indicated that the transit peptide may comprise only 7 or 8 residues, which is atypically short for precursors to stromal proteins.

Acclimatization↗
PubMed2004

Variations in water status, gas exchange, and growth in Rosmarinus officinalis plants infected with Glomus deserticola under drought conditions.

The influence of the arbuscular mycorrhizal fungus Glomus deserticola on the water relations, gas exchange parameters, and vegetative growth of Rosmarinus officinalis plants under water stress was studied. Plants were grown with and without the mycorrhizal fungus under glasshouse conditions and subjected to water stress by withholding irrigation water for 14 days. Along the experimental period, a significant effect of the fungus on the plant growth was observed, and under water stress, mycorrhizal plants showed an increase in aerial and root biomass compared to non-mycorrhizal plants. The decrease in the soil water potential generated a decrease in leaf water potential (psi(l)) and stem water potential (psi(x)) of mycorrhizal and non-mycorrhizal plants, with this decrease being lower in mycorrhizal water-stressed plants. Mycorrhization also had positive effects on the root hydraulic conductivity (Lp) of water stressed plants. Furthermore, mycorrhizal-stressed plants showed a more important decrease in osmotic potential at full turgor (psi(os)) than did non-mycorrhizal-stressed plants, indicating the capacity of osmotic adjustment. Mycorrhizal infection also improved photosynthetic activity (Pn) and stomatal conductance (g(s)) in plants under water stress compared to the non-mycorrhizal-stressed plants. A similar behaviour was observed in the photochemical efficiency of PSII (Fv/Fm) with this parameter being lower in non-mycorrhizal plants than in mycorrhizal plants under water stress conditions. In the same way, under water restriction, mycorrhizal plants showed higher values of chlorophyll content than did non-mycorrhizal plants. Thus, the results obtained indicated that the mycorrhizal symbiosis had a beneficial effect on the water status and growth of Rosmarinus officinalis plants under water-stress conditions.

Biomass↗
PubMed2000

Food-related behaviors during drought: a study of rural Fulani, northeastern Nigeria.

Two rural settled Fulani villages in northeast Nigeria were surveyed for dietary practices and use of edible wild plants (n = 100 adult subjects). Dietary patterns and medical data were obtained for children under 5, pregnant and lactating women and the elderly. A diversified diet was maintained at both geographical locations through hunting, gathering, agriculture, horticulture, animal husbandry, food exchanges and cash purchases. Edible wild plants associated with children included fruits of baure (Ficus sycomorus), faru (Lannea schiniperi), giginya (Gardenia aqualla), kokiya (Strychnos spinosa) and nunu (Parinari curatellitolia). Leaves of shiwaka (Veronia colorate) were consumed by lactating women to stimulate breastmilk production. Generally, fruits of baure (Ficus sycomorus) were eaten to counter stomach pain; fruits of kisni (Bridelia ferruginea) were eaten to treat diarrhea; and bark of kuka (Adansonia digitata) was consumed for weight gain. Food storage was more important during wet seasons than dry because of local and regional flooding. Adult Fulani men rode to distant markets on bicycles, while women walked to market and in some instances expended 3200 kcal/day engaging in this activity.

Adult↗
PubMed2001

Accumulation of plastid lipid-associated proteins (fibrillin/CDSP34) upon oxidative stress, ageing and biotic stress in Solanaceae and in response to drought in other species.

Plastid lipid-associated proteins, also termed fibrillin/CDSP34 proteins, are known to accumulate in fibrillar-type chromoplasts such as those of ripening pepper fruit, and in leaf chloroplasts from Solanaceae plants under abiotic stress conditions. It is shown here that treatments generating active oxygen species (high light combined with low temperature, gamma irradiation or methyl viologen treatment) result in potato CDSP34 gene induction and protein accumulation in leaves. Using transgenic tomato plants containing the pepper fibrillin promoter, a significant increase in promoter activity in leaves subjected to biotic stress, namely bacterial infections, was observed. In WT, a higher level of the endogenous fibrillin/CDSP34 protein is also observed after infection by E. chrysanthemi strain 3739. In addition to stress-related induction, a progressive increase in the fibrillin promoter activity is noticed during ageing in various tomato photosynthetic tissues and this increase correlates with a higher abundance of the endogenous protein in WT leaves. It is proposed that a mechanism related to oxidative events plays an essential role in the regulation of fibrillin/CDSP34 genes during stress and also during development. Using a biolistic transient expression assay, the pepper fibrillin promoter is found to be active in various dicot species, but not in monocots. Further, substantially increased levels of fibrillin/ CDSP34 proteins are shown in various dicotyledonous and monocotyledonous plants in response to water deficit.

Adaptation, Physiological↗
PubMed2002

Drought until death do us part: a case study of the desiccation-tolerance of a tropical moist forest seedling-tree, Licania platypus (Hemsl.) Fritsch.

Studies of the desiccation tolerance of 15-month-old Licania platypus (Hemsl.) Fritsch seedlings were performed on potted plants. Pots were watered to field capacity and then dehydrated for 23-46 d to reach various visible wilting stages from slightly-wilted to dead. Root hydraulic conductance, k(r), was measured with a high-pressure flow meter and whole-stem hydraulic conductance, k(ws), was measured by a vacuum chamber method. Leaf punches were harvested for measurement of leaf water potential by a thermocouple psychrometer and for measurement of fresh- and dry-weight. L. platypus was surprisingly desiccation-tolerant, suggesting that most species of central Panama may be well adapted to the seasonality of rainfall in the region. The slightly-wilted stage corresponded to leaf water potentials and relative water contents of -2.7 MPa and 0.85, respectively, but plants did not die until these values fell to -7.5 MPa and 0.14, respectively. As desiccation proceeded k(r) and k(ws) declined relative to irrigated controls, but k(ws) was more sensitive to desiccation than k(r). Values of k(ws) declined by 70-85% in slightly-wilted to dead plants, respectively. By comparison, k(r) showed no significant change in slightly-wilted plants and fell by about 50% in plants having severely-wilted to dead shoots.

Adaptation, Physiological↗
PubMed2006

Drought effects on carbon and nitrogen metabolism of pea nodules can be mimicked by paraquat: evidence for the occurrence of two regulation pathways under oxidative stresses.

Biological nitrogen fixation (BNF) is dramatically affected by environmental constraints such as water stress or heavy metals. It has been reported that these stresses induce the over-production of reactive oxygen species (ROS) and, in turn, oxidative stress that may be responsible for the above-mentioned BNF decline at the molecular level. Oxidative stress, occurring under different environmental stresses, has been widely related to physiological damage. However, a direct relationship between oxidative stress and the decline of BNF, independently from any other cellular damage resulting from adverse environmental situations, has yet to be demonstrated. In order to study the likely in vivo relationship between ROS and BNF inhibition in the legume-Rhizobium symbiosis, two paraquat (PQ) doses, 1 (LPQ) and 10 (HPQ) mmol m(-3), were applied to pea roots for 96 h in order to exacerbate ROS production. Whole-plant physiology and nodule metabolism parameters were determined every 24 h to monitor the evolution of plant responses to ROS. LPQ provoked BNF decline, which was preceded by a prior decrease in sucrose synthase (SS) activity. However, HPQ gave rise to a faster and more pronounced BNF inhibition, which coincided with a decline in SS and also with a reduction in leghaemoglobin (Lb) content. These results indicate a likely involvement of ROS in the effects of environmental stresses on BNF. Furthermore, these results support the occurrence of two regulation pathways for BNF under oxidative stress, one of these involving carbon shortage and the other involving Lb/oxygen flux.

Carbon↗
PubMed2004

Overexpression of the Arabidopsis 14-3-3 protein GF14 lambda in cotton leads to a "stay-green" phenotype and improves stress tolerance under moderate drought conditions.

The Arabidopsis gene GF14 lambda that encodes a 14-3-3 protein was introduced into cotton plants to explore the physiological roles that GF14 lambda might play in plants. The expression level of GF14 lambda under the control of the cauliflower mosaic virus 35S promoter varied in transgenic cotton plants, and lines that expressed GF14 lambda demonstrated a "stay-green" phenotype and improved water-stress tolerance. These lines wilted less and maintained higher photosynthesis than segregated non-transgenic control plants under water-deficit conditions. Stomatal conductance appears to be the major factor for the observed higher photosynthetic rates under water-deficit conditions. The stomatal aperture of transgenic plants might be regulated by GF14 lambda through some transporters such as H(+)-ATPase whose activities are controlled by their interaction with 14-3-3 proteins. However, since 14-3-3 proteins interact with numerous proteins in plant cells, many metabolic processes could be affected by the GF14 lambda overexpression. Whatever the mechanisms, the traits observed in the GF14 lambda-expressing cotton plants are beneficial to crops under certain water-deficit conditions.

14-3-3 Proteins↗
PubMed1995

Mechanisms of drought response in Thuja occidentalis L. I. Water stress conditioning and osmotic adjustment.

We investigated the extent of osmotic adjustment and changes in transpiration rate that occur in response to repeated cycles of water deficit stress in 6-year-old Thuja occidentalis L. (eastern white cedar) trees. Groups of trees were water-stress conditioned by repeated exposure to predetermined thresholds of nonlethal water stress by withholding water until the predawn water potential fell to -0.9 (mild conditioning) or -1.4 MPa (moderate conditioning). Both the mild and moderate conditioning treatments resulted in a decrease in osmotic potential of 0.08 to 0.20 MPa and 0.11 to 0.28 MPa, respectively, relative to the well-watered controls. Mildly and moderately conditioned trees exhibited an approximately 35 and 50% reduction in cumulative transpiration, respectively, following at least two stress cycles. Transpiration rates of conditioned trees remained below those of the well-watered controls even when water potential integrals were similar. We conclude that the decrease in transpiration rate was more important than osmotic adjustment as a mechanism of response to repeated water stress.

Journal Article↗
PubMed2004

Sclerophylly and leaf anatomical traits of five field-grown olive cultivars growing under drought conditions.

Leaf-level morphological and structural adaptations to reduce water loss were examined in five olive (Olea europaea L.) tree cultivars (Arbequina, Blanqueta, Cobrançosa, Manzanilla and Negrinha) growing under field conditions with low water availability. Leaf measurements included leaf tissue thickness, stomatal density, leaf area, leaf mass per unit area, density of leaf tissue, relative water content, succulence, water saturation deficit, water content at saturation and cuticular transpiration rate. We found considerable genotypic differences among the cultivars. Negrinha, Manzanilla and Cobrançosa had more morphological and structural leaf adaptations to protect against water loss than the other cultivars. Manzanilla and Negrinha enhanced their sclerophylly by building parenchyma tissues and increasing protective structures like the upper cuticle and both the upper and lower epidermis. Cobrançosa exhibited good protection against water loss through high density of foliar tissue and by thick cuticle and trichome layers. Compared with the Negrinha, Manzanilla and Cobrançosa cultivars, Arbequina leaves had a thinner trichome layer, implying that the leaves were less protected against water loss; however, the development of smaller leaves may reduce water loss at the whole-plant level. Among cultivars, Blanqueta had the largest leaves and some anatomical traits that may lead to high water loss, especially from the adaxial surface. The mechanisms employed by the cultivars to cope with summer stress are discussed at the morpho-structural level.

Dehydration↗
PubMed2005

Modeling tree water deficit from microclimate: an approach to quantifying drought stress.

Tree water deficit estimated by measuring water-related changes in stem radius (DeltaW) was compared with tree water deficit estimated from the output of a simple, physiologically reasonable model (DeltaWE), with soil water potential (Psisoil) and atmospheric vapor pressure deficit (VPD) as inputs. Values of DeltaW were determined by monitoring stem radius changes with dendrometers and detrending the results for growth. We followed changes in DeltaW and DeltaWE in Pinus sylvestris L. and Quercus pubescens Willd. over 2 years at a dry site (2001-2002; Salgesch, Wallis) and in Picea abies (L.) Karst. for 1 year at a wet site (1998; Davos, Graubuenden) in the Swiss Alps. The seasonal courses of DeltaW in deciduous species and in conifers at the same site were similar and could be largely explained by variation in DeltaWE. This finding strongly suggests that DeltaW, despite the known species-specific differences in stomatal response to microclimate, is mainly explained by a combination of atmospheric and soil conditions. Consequently, we concluded that trees are unable to maintain any particular DeltaW. Either Psisoil or VPD alone provided poorer estimates of DeltaW than a model incorporating both factors. As a first approximation of DeltaWE, Psisoil can be weighted so that the negative mean Psisoil reaches 65 to 75% of the positive mean daytime VPD over a season (Q. pubescens: approximately 65%, P. abies: approximately 70%, P. sylvestris: approximately 75%). The differences in DeltaW among species can be partially explained by a different weighting of Psisoil against VPD. The DeltaW of P. sylvestris was more dependent on Psisoil than that of Q. pubescens, but less than that of P. abies, and was less dependent on VPD than that of P. abies and Q. pubescens. The model worked well for P. abies at the wet site and for Q. pubescens and P. sylvestris at the dry site, and may be useful for estimating water deficit in other tree species.

Climate↗