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PubMed2005

Drought effects on hydraulic conductivity and xylem vulnerability to embolism in diverse species and provenances of Mediterranean cedars.

We studied hydraulic traits of young plants of the Mediterranean cedar species Cedrus atlantica (Endl.) G. Manetti ex Carrière (Luberon, France), C. brevifolia (Hook. f.) Henry (Cyprus), C. libani A. Rich (Hadeth El Jebbe, Lebanon) and C. libani (Armut Alani, Turkey). With an optimum water supply, no major differences were observed among species or provenances in either stem hydraulic conductivity (Ks) or leaf specific conductivity (Kl) measured on the main shoot. A moderate soil drought applied for 10 weeks induced marked acclimation through a reduction in Ks, particularly in the Lebanese provenance of C. libani, and a decrease in tracheid lumen size in all species. Cedrus atlantica, which had the smallest tracheids, was the species most vulnerable to embolism: a 50% loss in hydraulic conductivity (PsiPLC50) occurred at a water potential of -4.4 MPa in the well-watered treatment, and at -6.0 MPa in the moderate drought treatment. In the other species, PsiPLC50 was unaffected by moderate soil drought, and only declined sharply at water potentials between -6.4 and -7.5 MPa in both irrigation treatments. During severe drought, Ks of twigs and stomatal conductance (g(s)) were measured simultaneously as leaf water potential declined. For all species, lower vulnerability to embolism based on loss of Ks was recorded on current-year twigs. The threshold for stomatal closure (10% of maximum g(s)) was reached at a predawn water potential (Psi(pd)) of -2.5 MPa in C. atlantica (Luberon) and at -3.1 MPa in C. libani (Lebanon), whereas the other provenance and species had intermediate Psi(pd) values. Cedrus brevifolia, with a Psi(pd) (-3.0 MPa) close to that of C. libani (Lebanon), had the highest stomatal conductance of the study species. The importance of a margin of safety between water potential causing stomatal closure and that causing xylem embolism induction is discussed.

Cedrus↗

PubMed2006

Metabolic responses to water deficit in two Eucalyptus globulus clones with contrasting drought sensitivity.

We compared the metabolic responses of leaves and roots of two Eucalyptus globulus Labill. clones differing in drought sensitivity to a slowly imposed water deficit. Responses measured included changes in concentrations of soluble and insoluble sugars, proline, total protein and several antioxidant enzymes. In addition to the general decrease in growth caused by water deficit, we observed a decrease in osmotic potential when drought stress became severe. In both clones, the decrease was greater in roots than in leaves, consistent with the observed increases in concentrations of soluble sugars and proline in these organs. In roots of both clones, glutathione reductase activity increased significantly in response to water deficit, suggesting that this enzyme plays a protective role in roots during drought stress by catalyzing the catabolism of reactive oxygen species. Clone CN5 has stress avoidance mechanisms that account for its lower sensitivity to drought compared with Clone ST51.

Adaptation, Physiological↗

PubMed1990

Accumulation of free amino acids in the shoots and roots of three northern conifers during drought.

The effects of drought on the free amino acid pools in 21- to 23-week-old seedlings of black spruce (Picea mariana (Mill.) Britt.), white spruce (Picea glauca (Moench.) Voss) and jack pine (Pinus banksiana Lamb.) were followed during soil drying. Although water and pressure potentials were sensitive to water deficits, large changes in osmotic potential were not recorded until after the development of severe drought. Total soluble amino nitrogen in the shoots and roots of the three species rose as turgor declined, with peak concentrations attained late in the drought period when the pressure potentials of the shoots approached zero. All white spruce seedlings were alive at zero turgor and showed large decrements in osmotic potential, but concentrations of free amino nitrogen in the roots and shoots showed only modest increases, reaching 125 to 150% of their control values. In contrast, large numbers of black spruce and jack pine were dead or severely damaged at zero turgor, and only small changes in osmotic potential were detected during soil drying. Nevertheless, concentrations of soluble amino nitrogen in both species reached 150 to 200% of control values a few days before the seedlings died. Alanine, arginine, aspartic acid/asparagine, glutamic acid/glutamine, glycine, hydroxyproline and proline were the major components of the free amino acid pools under both water-stressed and non-stressed conditions, with the largest and most consistent increases observed in the roots of all three conifers. Although proline was an important and dynamic component of the free pools, absolute concentrations were commony equalled or exceeded by other free amino acids in the roots and shoots and nearly always exceeded by the concentration of aspartic acid/asparagine in both tissues. Differences in drought resistance among the three conifers were not reflected by unique patterns of amino acid accumulation or by large differences in absolute concentrations of the free amino acid pools.

Journal Article↗

PubMed1990

Drought adaptations and responses in five genotypes of Fraxinus pennsylvanica Marsh.: photosynthesis, water relations and leaf morphology.

Genotypic variation in photosynthesis and plant water relations during drought, and in leaf and seedling morphology were examined in greenhouse-grown Fraxinus pennsylvanica Marsh. (green ash) from five populations located along an east-west transect from New York State to South Dakota. During a 17-day drought, South Dakota seedlings, from the most xeric habitat, maintained the highest net photosynthesis and leaf conductance, and New York seedlings, from the most mesic habitat, exhibited the lowest net photosynthesis and leaf conductance. All populations except New York adjusted osmotically during the 17-day drought, by the end of which New York seedlings had the highest osmotic potentials at full and zero turgor. Tissue elasticity increased in New York seedlings, but decreased in Nebraska seedlings during the drought. Leaves of South Dakota seedlings were the most xerophytic. They were smaller in area and greater in thickness and specific mass than leaves of other sources. Leaves of New York seedlings were thinner than those of the other genotypes and among the largest. Seedlings from South Dakota were smaller than those of the other populations.

Journal Article↗

PubMed2002

Soluble invertase expression is an early target of drought stress during the critical, abortion-sensitive phase of young ovary development in maize.

To distinguish their roles in early kernel development and stress, expression of soluble (Ivr2) and insoluble (Incw2) acid invertases was analyzed in young ovaries of maize (Zea mays) from 6 d before (-6 d) to 7 d after pollination (+7 d) and in response to perturbation by drought stress treatments. The Ivr2 soluble invertase mRNA was more abundant than the Incw2 mRNA throughout pre- and early post-pollination development (peaking at +3 d). In contrast, Incw2 mRNAs increased only after pollination. Drought repression of the Ivr2 soluble invertase also preceded changes in Incw2, with soluble activity responding before pollination (-4 d). Distinct profiles of Ivr2 and Incw2 mRNAs correlated with respective enzyme activities and indicated separate roles for these invertases during ovary development and stress. In addition, the drought-induced decrease and developmental changes of ovary hexose to sucrose ratio correlated with activity of soluble but not insoluble invertase. Ovary abscisic acid levels were increased by severe drought only at -6 d and did not appear to directly affect Ivr2 expression. In situ analysis showed localized activity and Ivr2 mRNA for soluble invertase at sites of phloem-unloading and expanding maternal tissues (greatest in terminal vascular zones and nearby cells of pericarp, pedicel, and basal nucellus). This early pattern of maternal invertase localization is clearly distinct from the well-characterized association of insoluble invertase with the basal endosperm later in development. This localization, the shifts in endogenous hexose to sucrose environment, and the distinct timing of soluble and insoluble invertase expression during development and stress collectively indicate a key role and critical sensitivity of the Ivr2 soluble invertase gene during the early, abortion-susceptible phase of development.

Abscisic Acid↗

PubMed2003

Monitoring expression profiles of rice genes under cold, drought, and high-salinity stresses and abscisic acid application using cDNA microarray and RNA gel-blot analyses.

To identify cold-, drought-, high-salinity-, and/or abscisic acid (ABA)-inducible genes in rice (Oryza sativa), we prepared a rice cDNA microarray including about 1700 independent cDNAs derived from cDNA libraries prepared from drought-, cold-, and high-salinity-treated rice plants. We confirmed stress-inducible expression of the candidate genes selected by microarray analysis using RNA gel-blot analysis and finally identified a total of 73 genes as stress inducible including 58 novel unreported genes in rice. Among them, 36, 62, 57, and 43 genes were induced by cold, drought, high salinity, and ABA, respectively. We observed a strong association in the expression of stress-responsive genes and found 15 genes that responded to all four treatments. Venn diagram analysis revealed greater cross talk between signaling pathways for drought, ABA, and high-salinity stresses than between signaling pathways for cold and ABA stresses or cold and high-salinity stresses in rice. The rice genome database search enabled us not only to identify possible known cis-acting elements in the promoter regions of several stress-inducible genes but also to expect the existence of novel cis-acting elements involved in stress-responsive gene expression in rice stress-inducible promoters. Comparative analysis of Arabidopsis and rice showed that among the 73 stress-inducible rice genes, 51 already have been reported in Arabidopsis with similar function or gene name. Transcriptome analysis revealed novel stress-inducible genes, suggesting some differences between Arabidopsis and rice in their response to stress.

Abscisic Acid↗

PubMed1995

Improved Performance of Transgenic Fructan-Accumulating Tobacco under Drought Stress.

Fructans are polyfructose molecules produced by approximately 15% of the flowering plant species. It is possible that, in addition to being a storage carbohydrate, fructans have other physiological roles. Owing to their solubility they may help plants survive periods of osmotic stress induced by drought or cold. To investigate the possible functional significance of fructans, use was made of transgenic tobacco (Nicotiana tabacum) plants that accumulate bacterial fructans and hence possess an extra sink for carbohydrate. Biomass production was analyzed during drought stress with the use of lines differing only in the presence of fructans. Fructan-producing tobacco plants performed significantly better under polyethylene-glycol-mediated drought stress than wild-type tobacco. The growth rate of the transgenic plants was significantly higher (+55%), as were fresh weight (+33%) and dry weight (+59%) yields. The difference in weight was observed in all organs and was particularly pronounced in roots. Under unstressed control conditions the presence of fructans had no significant effect on growth rate and yield. Under all conditions the total nonstructural carbohydrate content was higher in the transgenic plants. We conclude that the introduction of fructans in this non-fructan-producing species mediates enhanced resistance to drought stress.

Journal Article↗

PubMed1995

Lipid Composition and Protein Dynamics in Thylakoids of Two Wheat Cultivars Differently Sensitive to Drought.

Two wheat (Triticum durum Desf.) cultivars with different sensitivities to drought were either grown under regular irrigation or subjected to water deficit by withholding water for 14 d. Water-stressed plants of both cultivars underwent similar decreases in leaf water potential, but the drought-tolerant cultivar showed higher relative water content and turgor. Neither osmotic nor elastic adjustment mechanisms appeared to be active under the conditions described here. Thylakoids isolated from the stressed, drought-tolerant wheat showed an increase in lipid-to-protein ratio, in comparison with the control, whereas this ratio remained unchanged in the sensitive wheat. In both cultivars, water deficit determined different rearrangements in the composition of the thylakoid individual polar lipids, but their unsaturation level remained unaffected with the exception of monogalactosyldiacylglycerol. In the drought-sensitive cultivar, an accumulation of free fatty acids together with a reduction in polar lipid amount was observed. Electron paramagnetic resonance measurements of spin-labeled proteins of stressed plants from the sensitive cv Adamello showed a higher spin label rotational correlation time together with lower sulphydryl group and mobile proteic portion levels, in comparison with the control. In the tolerant cv Ofanto, the first two parameters changed to a lesser extent following water depletion, and the mobile proteic portion was not altered.

Journal Article↗

PubMed1997

Increased Salt and Drought Tolerance by D-Ononitol Production in Transgenic Nicotiana tabacum L.

A cDNA encoding myo-inositol O-methyltransferase (IMT1) has been transferred into Nicotiana tabacum cultivar SR1. During drought and salt stress, transformants (I5A) accumulated the methylated inositol D-ononitol in amounts exceeding 35 [mu]mol g-1 fresh weight In I5A, photosynthetic CO2 fixation was inhibited less during salt stress and drought, and the plants recovered faster than wild type. One day after rewatering drought-stressed plants, I5A photosynthesis had recovered 75% versus 57% recovery with cultivar SR1 plants. After 2.5 weeks of 250 mM NaCl in hydroponic solution, I5A fixed 4.9 [plus or minus] 1.4 [mu]mol CO2 m-2 s-1, whereas SR1 fixed 2.5 [plus or minus] 0.6 [mu]mol CO2 m-2 s-1. myo-Inositol, the substrate for IMT1, increases in tobacco under stress. Preconditioning of I5A plants in 50 mM NaCl increased D-ononitol amounts and resulted in increased protection when the plants were stressed subsequently with 150 mM NaCl. Pro, Suc, Fru, and Glc showed substantial diurnal fluctuations in amounts, but D-ononitol did not. Plant transformation resulting in stress-inducible, stable solute accumulation appears to provide better protection under drought and salt-stress conditions than strategies using osmotic adjustment by metabolites that are constitutively present.

Journal Article↗

PubMed1998

Ultraviolet-B radiation effects on water relations, leaf development, and photosynthesis in droughted pea plants

The effects of ultraviolet-B (UV-B) radiation on water relations, leaf development, and gas-exchange characteristics in pea (Pisum sativum L. cv Meteor) plants subjected to drought were investigated. Plants grown throughout their development under a high irradiance of UV-B radiation (0.63 W m-2) were compared with those grown without UV-B radiation, and after 12 d one-half of the plants were subjected to 24 d of drought that resulted in mild water stress. UV-B radiation resulted in a decrease of adaxial stomatal conductance by approximately 65%, increasing stomatal limitation of CO2 uptake by 10 to 15%. However, there was no loss of mesophyll light-saturated photosynthetic activity. Growth in UV-B radiation resulted in large reductions of leaf area and plant biomass, which were associated with a decline in leaf cell numbers and cell division. UV-B radiation also inhibited epidermal cell expansion of the exposed surface of leaves. There was an interaction between UV-B radiation and drought treatments: UV-B radiation both delayed and reduced the severity of drought stress through reductions in plant water-loss rates, stomatal conductance, and leaf area.

Journal Article↗

PubMed2000

A stress-inducible gene for 9-cis-epoxycarotenoid dioxygenase involved in abscisic acid biosynthesis under water stress in drought-tolerant cowpea.

Four cDNA clones named CPRD (cowpea responsive to dehydration) corresponding to genes that are responsive to dehydration were isolated using differential screening of a cDNA library prepared from 10-h dehydrated drought-tolerant cowpea (Vigna unguiculata) plants. One of the cDNA clones has a homology to 9-cis-epoxycarotenoid dioxygenase (named VuNCED1), which is supposed to be involved in abscisic acid (ABA) biosynthesis. The GST (glutathione S-transferase)-fused protein indicates a 9-cis-epoxycarotenoid dioxygenase activity, which catalyzes the cleavage of 9-cis-epoxycarotenoid. The N-terminal region of the VuNCED1 protein directed the fused sGFP (synthetic green-fluorescent protein) into the plastids of the protoplasts, indicating that the N-terminal sequence acts as a transit peptide. Both the accumulation of ABA and expression of VuNCED1 were strongly induced by drought stress in the 8-d-old cowpea plant, whereas drought stress did not trigger the expression of VuABA1 (accession no. AB030295) gene that encodes zeaxanthin epoxidase. These results indicate that the VuNCED1 cDNA encodes a 9-cis-epoxycarotenoid dioxygenase and that its product has a key role in the synthesis of ABA under drought stress.

Abscisic Acid↗

PubMed2001

Nitric oxide induces stomatal closure and enhances the adaptive plant responses against drought stress.

Nitric oxide (NO) is a very active molecule involved in many and diverse biological pathways where it has proved to be protective against damages provoked by oxidative stress conditions. In this work, we studied the effect of two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine SNP-treated on the response of wheat (Triticum aestivum) to water stress conditions. After 2 and 3 h of drought, detached wheat leaves pretreated with 150 microM SNP retained up to 15% more water than those pretreated with water or NO(2)(-)/NO(3)(-). The effect of SNP treatment on water retention was also found in wheat seedlings after 7 d of drought. These results were consistent with a 20% decrease in the transpiration rate of SNP-treated detached wheat leaves for the same analyzed time. In parallel experiments, NO was also able to induce a 35%, 30%, and 65% of stomatal closure in three different species, Tradescantia sp. (monocotyledonous) and two dicotyledonous, Salpichroa organifolia and fava bean (Vicia faba), respectively. In SNP-treated leaves of Tradescantia sp., the stomatal closure was correlated with a 10% increase on RWC. Ion leakage, a cell injury index, was 25% lower in SNP-treated wheat leaves compared with control ones after the recovery period. Carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), a specific NO scavenger, reverted SNP action by restoring the transpiration rate, stomatal aperture, and the ion leakage to the level found in untreated leaves. Northern-blot analysis showed that SNP-treated wheat leaves display a 2-fold accumulation of a group three late embryogenesis abundant transcript with respect to control leaves both after 2 and 4 h of drought periods. All together, these results suggest that the exogenous application of NO donors might confer an increased tolerance to severe drought stress conditions in plants.

Adaptation, Physiological↗

PubMed1985

Drought-induced increases in abscisic Acid levels in the root apex of sunflower.

Abscisic acid (ABA) levels in 3-mm apical root segments of slowly droughted sunflower plants (Helianthus annuus L. cv Russian Giant) were analyzed as the methyl ester by selected ion monitoring gas chromatography-mass spectrometry using characteristic ions. An internal standard, hexadeuterated ABA (d6ABA) was used for quantitative analysis. Sunflower seedlings, grown in aeroponic chambers, were slowly droughted over a 7-day period. Drought stress increased ABA levels in the root tips at 24, 72, and 168 hour sample times. Control plants had 57 to 106 nanograms per gram ABA dry weight in the root tips (leaf water potential, -0.35 to -0.42 megapascals). The greatest increase in ABA, about 20-fold, was found after 72 hours of drought (leaf water potential, -1.34 to -1.47 megapascals). Levels of ABA also increased (about 7- to 54-fold) in 3-mm apical root segments which were excised and then allowed to dessicate for 1 hour at room temperature.

Journal Article↗

PubMed1986

Chlorophyll a Fluorescence and Photosynthetic and Growth Responses of Pinus radiata to Phosphorus Deficiency, Drought Stress, and High CO(2).

Needles from phosphorus deficient seedlings of Pinus radiata D. Don grown for 8 weeks at either 330 or 660 microliters CO(2) per liter displayed chlorophyll a fluorescence induction kinetics characteristic of structural changes within the thylakoid chloroplast membrane, i.e. constant yield fluorescence (F(O)) was increased and induced fluorescence ([F(P)-F(I)]/F(O)) was reduced. The effect was greatest in the undroughted plants grown at 660 mul CO(2) L(-1). By week 22 at 330 mul CO(2) L(-1) acclimation to P deficiency had occurred as shown by the similarity in the fluorescence characteristics and maximum rates of photosynthesis of the needles from the two P treatments. However, acclimation did not occur in the plants grown at 660 mul CO(2) L(-1). The light saturated rate of photosynthesis of needles with adequate P was higher at 660 mul CO(2) L(-1) than at 330 mul CO(2) L(-1), whereas photosynthesis of P deficient plants showed no increase when grown at the higher CO(2) concentration. The average growth increase due to CO(2) enrichment was 14% in P deficient plants and 32% when P was adequate. In drought stressed plants grown at 330 mul CO(2) L(-1), there was a reduction in the maximal rate of quenching of fluorescence (R(Q)) after the major peak. Constant yield fluorescence was unaffected but induced fluorescence was lower. These results indicate that electron flow subsequent to photosystem II was affected by drought stress. At 660 mul CO(2) L(-1) this response was eliminated showing that CO(2) enrichment improved the ability of the seedlings to acclimate to drought stress. The average growth increase with CO(2) enrichment was 37% in drought stressed plants and 19% in unstressed plants.

Journal Article↗

PubMed1986

Osmotic Adjustment in Leaves of VA Mycorrhizal and Nonmycorrhizal Rose Plants in Response to Drought Stress.

Osmotic adjustment in Rosa hybrida L. cv Samantha was characterized by the pressure-volume approach in drought-acclimated and unacclimated plants brought to the same level of drought strain, as assayed by stomatal closure. Plants were colonized by either of the vesicular-arbuscular mycorrhizal fungi Glomus deserticola Trappe, Bloss and Menge or G. intraradices Schenck and Smith, or were nonmycorrhizal. Both the acclimation and the mycorrhizal treatments decreased the osmotic potential (Psi(pi)) of leaves at full turgor and at the turgor loss point, with a corresponding increase in pressure potential at full turgor. Mycorrhizae enabled plants to maintain leaf turgor and conductance at greater tissue water deficits, and lower leaf and soil water potentials, when compared with nonmycorrhizal plants. As indicated by the Psi(pi) at the turgor loss point, the active Psi(pi) depression which attended mycorrhizal colonization alone was 0.4 to 0.6 megapascals, and mycorrhizal colonization and acclimation in concert 0.6 to 0.9 megapascals, relative to unacclimated controls without mycorrhizae. Colonization levels and sporulation were higher in plants subjected to acclimation. In unacclimated hosts, leaf water potential, water saturation deficit, and soil water potential at a particular level of drought strain were affected most by G. intraradices. G. deserticola had the greater effect after drought preconditioning.

Journal Article↗

PubMed1987

Effects of drought on primary photosynthetic processes of cotton leaves.

The effects of drought on Photosystem II (PSII) fluorescence and photosynthetic electron transport activities were analyzed in cotton. Water stress did not modify the amplitude of leaf variable fluorescence at room temperature in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) nor at 77 K. It is therefore concluded that photon collection, their distribution between the two photosystems, and PSII photochemistry are unaffected by the stress. In droughted leaves at room temperature under low exciting light, the transitory maximum (F(p)) and steady state (F(t)) fluorescence levels are increased; under high exciting light, F(p) level and the rise time from the initial level (F(o)) to F(p) are unchanged, whereas F(p) to F(t) decay time is increased. These results infer that the drought slows the rate of plastoquinone reoxidation. This conclusion agrees with a larger proportion of reduced primary PSII electron acceptor Q(A) measured at the steady state under low light. In thylakoids isolated from droughted leaves, PSII mediated electron flow was the same as in thylakoids from control leaves, whereas PSI mediated electron transport was inhibited. It is shown that water stress does not induce sensitization to photoinhibition in cotton.

Journal Article↗

PubMed1987

Water Transfer in an Alfalfa/Maize Association : Survival of Maize during Drought.

We investigated the possibility of interspecific water transfer in an alfalfa (Medicago sativa L.) and maize (Zea mays L.) association. An alfalfa plant was grown through two vertically stacked plastic tubes. A 5 centimeter air gap between tubes was bridged by alfalfa roots. Five-week old maize plants with roots confined to the top tube were not watered, while associated alfalfa roots had free access to water in the bottom tube (the -/+ treatment). Additional treatments included: top and bottom tubes watered (+/+), top and bottom tubes droughted (-/-), and top tube droughted after removal of alfalfa root bridges and routine removal of alfalfa tillers (-(*)). Predawn leaf water potential of maize in the -/+ treatment fell to -1.5 megapascals 13 days after the start of drought; thereafter, predawn and midday potentials were maintained near -1.9 megapascals. Leaf water potentials of maize in the -/- and -(*) treatments declined steadily; all plants in these treatments were completely desiccated before day 50. High levels of tritium activity were detected in water extracted from both alfalfa and maize leaves after (3)H(2)O was injected into the bottom -/+ tube at day 70 or later. Maize in the -/+ treatment was able to survive an otherwise lethal period of drought by utilizing water lost by alfalfa roots.

Journal Article↗

PubMed1987

Drought-Induced Changes in Protein Patterns of Brassica napus var. oleifera Roots.

Drought-induced changes in two-dimensional silver stained protein patterns of Brassica napus L. var. oleifera M. root system were detected both at quantitative and qualitative levels. Particularly, 13 new polypeptides of low molecular weight were evidenced in the drought-stressed tap root, 12 of which were also present in the short tuberized roots, a specific drought-induced root type. The reversibility of these modifications, observed after 3 days rehydration, suggests that they might be involved in drought tolerance.

Journal Article↗