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PubMed1990

Interactions between Sitka spruce, the green spruce aphid, sulphur dioxide pollution and drought.

Sitka spruce trees, with and without the aphid Elatobium abietinum and/or drought treatment, were subjected to 25 nl litre(-1) of sulphur dioxide over a 2-month period. Aphids became three times as abundant on the fumigated trees if they were well watered and twice as abundant on trees from which water was withheld, compared with unfumigated controls. Growth parameters of the trees were little affected by pollution alone, but were substantially reduced by either aphids or drought. There was a significant interaction between SO(2) and aphids in a further reduction of both leader extension and root weight. Root weight was also reduced by 24% more than expected from the additive effects of the combined SO(2) and drought treatment.

Journal Article↗
PubMed2005

Cold, salinity and drought stresses: an overview.

World population is increasing at an alarming rate and is expected to reach about six billion by the end of year 2050. On the other hand food productivity is decreasing due to the effect of various abiotic stresses; therefore minimizing these losses is a major area of concern for all nations to cope with the increasing food requirements. Cold, salinity and drought are among the major stresses, which adversely affect plants growth and productivity; hence it is important to develop stress tolerant crops. In general, low temperature mainly results in mechanical constraint, whereas salinity and drought exerts its malicious effect mainly by disrupting the ionic and osmotic equilibrium of the cell. It is now well known that the stress signal is first perceived at the membrane level by the receptors and then transduced in the cell to switch on the stress responsive genes for mediating stress tolerance. Understanding the mechanism of stress tolerance along with a plethora of genes involved in stress signaling network is important for crop improvement. Recently, some genes of calcium-signaling and nucleic acid pathways have been reported to be up-regulated in response to both cold and salinity stresses indicating the presence of cross talk between these pathways. In this review we have emphasized on various aspects of cold, salinity and drought stresses. Various factors pertaining to cold acclimation, promoter elements, and role of transcription factors in stress signaling pathway have been described. The role of calcium as an important signaling molecule in response to various stress signals has also been covered. In each of these stresses we have tried to address the issues, which significantly affect the gene expression in relation to plant physiology.

Acclimatization↗
PubMed2004

Drought acclimation reduces O2*- accumulation and lipid peroxidation in wheat seedlings.

Abiotic stresses cause ROS accumulation, which is detrimental to plant growth. It is well known that acclimation of plants under mild or sub-lethal stress condition leads to development of resistance in plants to severe or lethal stress condition. The generation of ROS and subsequent oxidative damage during drought stress is well documented in the crop plants. However, the effect of drought acclimation treatment on ROS accumulation and lipid peroxidation has not been examined so far. In this study, the effect of water stress acclimation treatment on superoxide radical (O(2)(-z.rad;)) accumulation and membrane lipid peroxidation was studied in leaves and roots of wheat (Triticum aestivum) cv. C306. EPR quantification of superoxide radicals revealed that drought acclimation treatment led to 2-fold increase in superoxide radical accumulation in leaf and roots with no apparent membrane damage. However under subsequent severe water stress condition, the leaf and roots of non-acclimated plants accumulated significantly higher amount of superoxide radicals and showed higher membrane damage than that of acclimated plants. Thus, acclimation-induced restriction of superoxide radical accumulation is one of the cellular processes that confers enhanced water stress tolerance to the acclimated wheat seedlings.

Acclimatization↗
PubMed2006

GmDREB2, a soybean DRE-binding transcription factor, conferred drought and high-salt tolerance in transgenic plants.

A novel DREB (dehydration responsive element binding protein) homologous gene, GmDREB2, was isolated from soybean. Based on its similarity with AP2 domains, GmDREB2 was classified into A-5 subgroup in DREB subfamily in AP2/EREBP family. Expression of GmDREB2 gene was induced by drought, high salt, and low temperature stresses and abscisic acid treatment. The GmDREB2 bound specifically to DRE element in vitro. Furthermore, the overexpression of GmDREB2 activated expression of downstream genes in transgenic Arabidopsis, resulting in enhanced tolerance to drought and high-salt stresses and did not cause growth retardation. Analysis of free proline contents in transgenic tobacco indicated that the overexpression of GmDREB2 accumulated higher level of free proline compared to the wild type plants under drought condition. The results from this study indicate that this novel soybean GmDREB2 gene functions as an important transcriptional activator and may be useful in improving of plant tolerance to abiotic stresses in plants.

Arabidopsis↗
PubMed2005

Arbuscular mycorrhizal fungi can contribute to maintain antioxidant and carbon metabolism in nodules of Anthyllis cytisoides L. subjected to drought.

The symbiosis legume-arbuscular mycorrhizal fungi-nitrogen fixing bacteria is of relevant interest in Mediterranean regions where Anthyllis cytisoides L. grows. In these areas, nitrogen is one of the nutrients that most limits plant growth. In addition, the long periods of water deficit decrease the diffusion rate of phosphorus and, consequently, also decrease the biological nitrogen fixation. It is well known that mycorrhizal fungi can improve phosphorus uptake and, recently, some authors have found that antioxidant activities in mycorrhizal plants can delay drought-induced nodule senescence. The objective of our work was to evaluate weather mycorrhizal fungi could preserve the nodule metabolism in A. cytisoides subjected to drought. Results showed that a low soil water content associated with an enhancement of soil compaction accelerated the senescence of nodules in both non-mycorrhizal and mycorrhizal plants. However, while total soluble protein, leghaemoglobin (Lb) content, as well as carbon and antioxidant metabolism significantly decreased in nodules from non-mycorrhizal A. cytisoides subjected to drought, nodules from stressed mycorrhizal plants maintained Lb levels, showed greater rates of carbon metabolism, and exhibited higher enzymatic activities related to the removal of reactive oxygen species. In addition to the greater activity of antioxidant enzymes, other mechanisms related or unrelated to enhanced nodule water status could also be implied in the better nodule functioning observed in mycorrhizal plants under stressful conditions.

Antioxidants↗
PubMed2005

Expression analysis of a stress-modulated transcript in drought tolerant and susceptible cultivars of sorghum (Sorghum bicolor).

The present study reports the cloning of a 581 bp sequence, designated as SbEST8, from the osmotically stressed germinated seeds of a drought tolerant cultivar of sorghum (Sorghum bicolor). The SbEST8, which shows no homology with the reported gene sequences, is present in multiple copies and lacks restriction fragment length polymorphism among different sorghum cultivars. The expression of SbEST8 in the germinating seeds of sorghum was modulated by different abiotic stresses. Kinetic studies revealed that imposition of osmotic stress after 8h resulted in maximum levels of SbEST8 mRNA in the germinating seeds of cv. ICSV-272, with further stress causing a decline to undetectable levels by 16 h. However, relieving the stress after 12h resulted in an enhancement of SbEST8 mRNA levels for at least another 4h following which it declined. The decrease in SbEST8 mRNA levels in the leaves at 30 DAS in response to drought stress was observed only in the drought susceptible cultivar (CSV-216), whereas its expression was either increased substantially or remained unaffected in the tolerant cultivars, thus suggesting its role in water stress tolerance.

Cloning, Molecular↗
PubMed2005

Aluminium-induced drought and oxidative stress in barley roots.

The aim of the present study was to examine the relation between Al accumulation in root tissues, root growth inhibition, root water content, cell viability and expression of oxidative and drought stress-related genes in barley roots growing on the filter paper. Al-induced root growth inhibition correlated with Al uptake and cell death. Water content of Al-treated root represented only half of the control one. The expression of the dehydrin gene dhn4, which is a marker for drought stress in plant tissues, was strongly induced during Al stress. Al treatment also induced expression of oxidative stress-related genes such as glutathione peroxidase (gpx), pathogen-related peroxidase (prx8), glutathione reductase (gr) and dehydroascorbate reductase (dhar). The present results suggest correlation between Al uptake, Al-induced drought stress, oxidative stress, cell death and root growth inhibition.

Aluminum↗
PubMed2000

Involvement of CDSP 32, a drought-induced thioredoxin, in the response to oxidative stress in potato plants.

In animal cells, yeast and bacteria, thioredoxins are known to participate in the response to oxidative stress. We recently identified a novel type of plant thioredoxin named CDSP 32 for chloroplastic drought-induced stress protein of 32 kDa. In the present work, we measured comparable increases in the glutathione oxidation ratio and in the level of chlorophyll thermoluminescence, a specific marker for thylakoid lipid peroxidation in Solanum tuberosum plants subjected to drought or oxidative treatments (photooxidative stress, gamma irradiation and methyl viologen spraying). Further, substantial accumulations of CDSP 32 mRNA and protein were revealed upon oxidative treatments. These data show for the first time in plants the induction of a thioredoxin by oxidative stress. We conclude that CDSP 32 may preserve chloroplastic structures against oxidative injury upon drought.

Chlorophyll↗
PubMed2001

Citrulline, a novel compatible solute in drought-tolerant wild watermelon leaves, is an efficient hydroxyl radical scavenger.

Drought-tolerant wild watermelon accumulates high levels of citrulline in the leaves in response to drought conditions. In this work, the hydroxyl radical-scavenging activity of citrulline was investigated in vitro. The second-order rate constant for the reaction between citrulline and hydroxyl radicals was found to be 3.9x10(9) M(-1) s(-1), demonstrating that citrulline is one of the most efficient scavengers among compatible solutes examined so far. Moreover, citrulline effectively protected DNA and an enzyme from oxidative injuries. Liquid chromatography-mass spectrometry analysis revealed that at least four major products were formed by the reaction between citrulline and hydroxyl radicals. Activities of metabolic enzymes were not inhibited by up to 600 mM citrulline, indicating that citrulline does not interfere with cellular metabolism. We reasoned, from these results, that citrulline contributes to oxidative stress tolerance under drought conditions as a novel hydroxyl radical scavenger.

Citrulline↗
PubMed2000

Extreme variation in the concentration of trace metals in sediments and bivalves from the Bilbao estuary (Spain) caused by the 1989-90 drought.

Intertidal sediments and bivalves Scrobicularia plana from Bilbao estuary (Spain) were repeatedly sampled during and after the 1989-90 drought. The organic content (OC) and the concentration of most of the 10 metals analysed in sediments were extremely variable (e.g. Cd ranged from 4 to 112 micrograms g-1, ppm dry wt), and they were strongly related to an index applied to estimate the magnitude of the drought (namely the deficit flow of the main river). After OC normalisation, the correlation versus deficit was lost for some elements (Cr, Fe, Ni) but not for others (Cd, Co, Cu, Pb, Zn). This leads to the conclusion that both a natural and a man-induced process account for the observed rise and fall of the contamination pattern: the reduced river flow raised the metal-binding capacity of sediments, and restrictions in the water supply increased the corrosion of sewers and their leaching of some elements. The concentration of trace metals in local bivalves (Cd reached 100 and 458 ppm dry wt, respectively, for whole tissues and digestive gland) mirrored the sediment contamination dynamics, but at a slower pace. The means by which S. plana is able to tolerate such high Cd tissue levels remain unknown. These results constitute some prime field evidence of drought effects that should be born in mind when pollution and risk from climate change are assessed in estuaries.

Animals↗
PubMed2000

Water stress preconditioning to improve drought resistance in young apricot plants.

The effect of water stress preconditioning was studied in 1-year-old apricot plants (Prunus armeniaca L., cv. Búlida). Plants were submitted to different treatments, T-0 (control treatment) and T-1, drip irrigated daily; T-2 and T-3, irrigated daily at 50% and 25% of T-0, respectively; T-4 and T-5, irrigated to field capacity every 3 and 6 days, respectively. After 30 days, irrigation was withheld for 10 days, maintaining the T-0 treatment irrigated daily. After this period, the plants were re-irrigated to run-off and treated as control treatment. The stomatal closure and epinasty observed in response to water stress represented adaptive mechanisms to drought, allowing the plants to regulate water loss more effectively and prevent leaf heating. A substantial reduction in the irrigation water supplied combined with a high frequency of application (T-3 treatment) promoted plant hardening; the plants enduring drought better, due to their greater osmotic adjustment (0.77 MPa), which prevented severe plant dehydration and leaf abscission. Such a preconditioning treatment may be valuable for young apricot plants in the nursery stage in order to improve their subsequent resistance to drought. A 50% reduction in daily irrigation (T-2 treatment) did not significantly affect either gas exchange rates or leaf turgor, which suggests that water should be applied frequently if deficit irrigation is to be implemented.

Journal Article↗
PubMed2001

Compatibility of a wild type and its genetically modified Sinorhizobium strain with two mycorrhizal fungi on Medicago species as affected by drought stress.

The effect of double inoculation with two strains of Sinorhizobium meliloti [the wild type (WT) strain GR4 and its genetically modified (GM) derivative GR4(pCK3)], and two species of arbuscular mycorrhizal (AM) fungi (Glomus deserticola and Glomus intraradices) was examined in a microcosm system on three species of Medicago (M. nolana, M. rigidula, M. rotata). Two water regimes (80 and 100% water holding capacity, WHC) were assayed. The efficiency of each AM fungus increasing plant growth, nutrient content, nodulation and water-stress tolerance was related to the Sinorhizobium strains and Medicago species. This indicates selective and specific compatibilities between microsymbionts and the common host plant. Differential effects of the mycorrhizal isolates were not associated with their colonizing ability. Nodulation and mycorrhizal dependency (MD) changed in each plant genotype in accordance with the Sinorhizobium strain and AM fungi involved. Generally, Medicago sp. MD decreased under water-stress conditions even when these conditions did not affect AM colonization (%). Proline accumulation in non-mycorrhizal plant leaves was increased by water stress, except in M. rotata plants. Differences in proline accumulation in AM-colonized plants suggest that both the AM fungus and the Sinorhizobium strain were able to induce different degrees of osmotic adjustment. Mycorrhizal plants nodulated by the WT strain accumulated more proline in M. rigidula and M. rotata under water stress than non-mycorrhizal plants. Conversely, mycorrhizal plants nodulated by the GM strain accumulated less proline in response to both AM colonization and drought. These results indicated changes in the synthesis of this nitrogenous osmoregulator product associated with microbial inoculation and drought tolerance. Mycorrhizal plants nodulated by the GM Sinorhizobium strain seem to suffer less from the detrimental effect of water stress, since under water limitation relative plant growth, percentage of AM colonization, root dry weight and the highest R/S ratio remained the same. The fact that GM nodulated plants are better adapted to drought stress could be of practical interest and the management of GM microorganism inoculation may be crucial for biotechnological approaches to improving crop yield in dry environments.

Journal Article↗
PubMed2002

An evaluation of ozone exposure metrics for a seasonally drought-stressed ponderosa pine ecosystem.

Ozone stress has become an increasingly significant factor in cases of forest decline reported throughout the world. Current metrics to estimate ozone exposure for forest trees are derived from atmospheric concentrations and assume that the forest is physiologically active at all times of the growing season. This may be inaccurate in regions with a Mediterranean climate, such as California and the Pacific Northwest, where peak physiological activity occurs early in the season to take advantage of high soil moisture and does not correspond to peak ozone concentrations. It may also misrepresent ecosystems experiencing non-average climate conditions such as drought years. We compared direct measurements of ozone flux into a ponderosa pine canopy with a suite of the most common ozone exposure metrics to determine which best correlated with actual ozone uptake by the forest. Of the metrics we assessed, SUM0 (the sum of all daytime ozone concentrations > 0) best corresponded to ozone uptake by ponderosa pine, however the correlation was only strong at times when the stomata were unconstrained by site moisture conditions. In the early growing season (May and June). SUM0 was an adequate metric for forest ozone exposure. Later in the season, when stomatal conductance was limited by drought. SUM0 overestimated ozone uptake. A better metric for seasonally drought-stressed forests would be one that incorporates forest physiological activity, either through mechanistic modeling, by weighting ozone concentrations by stomatal conductance, or by weighting concentrations by site moisture conditions.

California↗
PubMed2002

Warm temperatures or drought during seed maturation increase free alpha-tocopherol in seeds of soybean (Glycine max [L.] Merr.).

Soybean seeds are an important source of dietary tocopherols, but like seeds of other dicotyledonous plants, they contain relatively little alpha-tocopherol, the form with the greatest vitamin E activity. To evaluate potential effects of environmental stress during seed maturation on tocopherols, soybeans were raised in greenhouses at nominal average temperatures of 23 degrees C or 28 degrees C during seed fill, with or without simultaneous drought (soil moisture at 10-25% of capacity), during normal growing seasons in 1999 (cvs. Essex and Forrest) and 2000 (cvs. Essex, Forrest, and Williams). Total free (nonesterified) tocopherols increased slightly in response to drought in Essex and Forrest. All three lines responded to elevated temperature and, to a lesser extent, drought with large (2-3-fold) increases in alpha-tocopherol and corresponding decreases in delta-tocopherol and gamma-tocopherol. The results suggest that weather or climate can significantly affect seed tocopherols. It may be possible to breed for elevated alpha-tocopherols by selecting for altered plant response to temperature.

Environment↗
PubMed2003

A comparative study of the effect of abscisic acid and cAMP on protein synthesis in wheat caryopses under drought conditions.

The effect of exogenous abscisic acid and cAMP on synthesis of soluble proteins in wheat caryopses in drought has been studied. Both compounds affected the formation of the polypeptides whose synthesis was stimulated by dehydration: they increased the incorporation of the label into polypeptides of 13, 15, and 26 kD and decreased the incorporation of the label into polypeptides of 14, 64, and 77 kD. Abscisic acid and cAMP increased the level of the incorporation of [(14)C]leucine into the low-molecular-weight polypeptides of 12, 17, and 19 kD whose synthesis was suppressed by drought. These data suggest that the cyclic adenylate signal system is probably involved in the effect of abscisic acid on protein synthesis in drought.

Abscisic Acid↗
PubMed2001

Leaf cuticular waxes of potted rose cultivars as affected by plant development, drought and paclobutrazol treatments.

The present work was carried out to evaluate how plant growth and cultural practices influence the amount and composition of cuticular waxes on leaves of rose cultivars. The total amount of cuticular wax per leaf area was higher for rose cultivar Apollo Parade than for Charming Parade. Both cultivars had waxes dominated by alkanes, with the major alkanes being the C31 and C33 homologues. Primary alcohols were the next most abundant constituent class, with C26 as the dominant homologue. Compared with Charming Parade, Apollo Parade had higher proportions of its total wax load as primary alcohols but lower acids and aldehydes. The proportion of alkanes in the total load on these cultivars was similar. Commercially produced roses are routinely treated with paclobutrazol (PBZ) to retard growth. PBZ treatments caused a 10% increase in total wax load and changes in the proportions of certain wax constituents within 11 days of application. Notable was an increase in the total proportion of acids in the total load 25 days after PBZ application, primarily because of increased C28 acids. An alternative method of retarding plant growth is production of roses under limited water availability. When Apollo Parade roses experienced periods of moderate drought stress during production, the wax load per leaf area increased 14 and 8% above control levels at 24 and 38 days after imposition of drought, respectively. Drought caused similar changes in the proportions of individual wax constituents as did PBZ application.

Journal Article↗
PubMed2002

Induction by pathogen, salt and drought of a basic class II chitinase mRNA and its in situ localization in pepper (Capsicum annuum).

Northern blot and in situ hybridization analyses revealed that a pepper basic class II chitinase gene (CAChi2) is constitutively expressed in floral organs and root endodermis, but not in leaf, stem and fruit of pepper. Resistance of pepper leaves to Colletotrichum coccodes infection at a late growth stage was correlated with induction of beta-1,3-glucanase and PR-1 mRNA, but not of chitinase (CAChi2) mRNA. Transcriptional activation of the CAChi2 gene in pepper leaves occurred during anthracnose development. The CAChi2 transcripts were mainly localized in phloem cells of vascular tissues of pepper leaves infected with C. coccodes. The CAChi2 gene was also differentially induced in leaf and stem tissue by treatment with abscisic acid (ABA), sodium chloride or drought. Strong accumulation of the CAChi2 transcripts occurred in pepper stem tissues due to high salt and drought, and also due to treatment with ABA. These results suggest involvement of the chitinase gene in protection of pepper plants against the pathogen, but also document cross talk with stress signals mediated by ABA, high salinity and drought.

Journal Article↗
PubMed2002

Winter-drought induced embolism in Norway spruce (Picea abies) at the Alpine timberline.

At the timberline in the Central Alps, climatic conditions during winter frequently cause excessive drought stress (frost drought, 'Frosttrocknis'), which we hypothesized to induce cavitation in trees. We investigated the extent of winter-embolism in Norway spruce (Picea abies (L.) Karst.) growing near the timberline and analysed adaptations in vulnerability and anatomy. We found conductivity losses of up to 100% at the highest elevation (2020 m) correlated with low water potentials down to - 4.0 MPa. Vulnerability thresholds (50% loss in conductivity) decreased from - 3.39 MPa at 800 m to - 3.88 MPa at 1600 m corresponding to a decrease in tracheid cross-sectional area as well as pit and pit pore diameters. These thresholds were lower than potentials measured in embolized twigs near the timberline at the sampling dates probably due to lower potentials and/or a role of freeze-thaw events earlier in winter. Data indicated refilling processes, which may be of particular relevance for trees at the timberline, since adaptations in drought-induced vulnerability failed to prevent winter-embolism.

Journal Article↗