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PubMed2003

Bundle sheath chloroplasts of rice are more sensitive to drought stress than mesophyll chloroplasts.

We investigated the effects of drought stress on the ultrastructure of chloroplasts in rice plants. After the seedlings were grown in a glasshouse for 1 month, they were treated for drought stress using two methods. One drought treatment was imposed by reducing the water supply to the plants for 1 month. The other was imposed by withholding water for 2 weeks to examine the withering process of leaves by drought stress. The ultrastructural changes of chloroplasts in bundle sheath cells were more prominent than those in mesophyll cells under both drought stress treatments. Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) content in bundle sheath chloroplasts reduced more dramatically than in mesophyll chloroplasts by drought stress. Although a slight swelling of thylakoids was sometimes observed in bundle sheath chloroplasts in moderate stress for 1 month, the thylakoids were less affected by drought stress than chloroplast envelope. These results suggest that chloroplasts in bundle sheath cells were more sensitive to drought stress than those in mesophyll cells and the thylakoids were less damaged by drought stress compared with chloroplast envelope.

Chloroplasts↗

PubMed2002

Genotypic variation for drought tolerance in Beta vulgaris.

Insufficient soil moisture during summer months is now the major cause of sugar beet yield losses in the UK. However, selection for increased drought tolerance has not been a breeding priority until recently. Genetic variation for drought tolerance is an essential prerequisite for the development of more stress-tolerant varieties, but commercial sugar beet varieties seem to have similar yield responses to drought. The objective of this study was to assess the degree of genotypic variation for drought tolerance within a wide range of sugar beet germplasm and genebank accessions within Beta. Thirty sugar beet genotypes were screened under field drought conditions, and putative drought tolerant and sensitive lines (in terms of yield reduction in polythene-covered vs. irrigated plots) were identified. Significant genotype x water treatment interactions were found for dry matter yield and relative leaf expansion rate. Genotypic differences for drought susceptibility index were also significant. Differential sensitivity of seedling shoot growth to water deficit was examined by comparing 350 genebank accessions in a simple growth chamber screen. Methods of data management were devised to highlight lines for entry into subsequent field tests. The results of the field and seedling screens indicate that there is variation for tolerance to water deficits within sugar beet and related types, and that there are lines that show greater drought tolerance than selected commercial varieties. Divergent lines showing contrasting behaviour should aid in the identification of key morpho-physiological traits that confer drought tolerance.

Acclimatization↗

PubMed2006

Identification of stress-responsive genes in an indica rice (Oryza sativa L.) using ESTs generated from drought-stressed seedlings.

The impacts of drought on plant growth and development limit cereal crop production worldwide. Rice (Oryza sativa) productivity and production is severely affected due to recurrent droughts in almost all agroecological zones. With the advent of molecular and genomic technologies, emphasis is now placed on understanding the mechanisms of genetic control of the drought-stress response. In order to identify genes associated with water-stress response in rice, ESTs generated from a normalized cDNA library, constructed from drought-stressed leaf tissue of an indica cultivar, Nagina 22 were used. Analysis of 7794 cDNA sequences led to the identification of 5815 rice ESTs. Of these, 334 exhibited no significant sequence homology with any rice ESTs or full-length cDNAs in public databases, indicating that these transcripts are enriched during drought stress. Analysis of these 5815 ESTs led to the identification of 1677 unique sequences. To characterize this drought transcriptome further and to identify candidate genes associated with the drought-stress response, the rice data were compared with those for abiotic stress-induced sequences obtained from expression profiling studies in Arabidopsis, barley, maize, and rice. This comparative analysis identified 589 putative stress-responsive genes (SRGs) that are shared by these diverse plant species. Further, the identified leaf SRGs were compared to expression profiles for a drought-stressed rice panicle library to identify common sequences. Significantly, 125 genes were found to be expressed under drought stress in both tissues. The functional classification of these 125 genes showed that a majority of them are associated with cellular metabolism, signal transduction, and transcriptional regulation.

Adaptation, Physiological↗

PubMed1996

Two-dimensional protein patterns of Arabidopsis wild-type and auxin insensitive mutants, axr1, axr2, reveal interactions between drought and hormonal responses.

In order to detect gene products involved in Arabidopsis drought adaptive strategy, 2D-PAGE protein patterns of two auxin-insensitive mutants, axr1, axr2, differentially affected in specific drought responses, were compared to the wild-type Columbia ecotype, in well-watered and drought-stressed conditions. Coupled to computer analysis of polypeptide amounts, 2D-electrophoresis revealed subtle changes in protein expression induced by progressive drought stress and/or mutations affecting the auxin response pathway. The differential protein patterns of axr1 and axr2 were consistent with their contrasting drought responses. The specific leaf and root protein patterns of axr1 showed that this mutation disrupts drought responses related to auxin regulation. In particular, the near absence of drought rhizogenesis in axr1 was associated with a root protein pattern closer to the well-watered than to the water-stressed axr2 and Columbia wild-type root protein patterns. Also, the largely different effects of axr1 and axr2 mutations suggest that they affect different pathways in auxin response. Several sets of polypeptides, whose regulation was affected by drought and/or mutation, were thus detected. These polypeptides could play a role both in the auxin and the drought response pathways. Their identification, through microsequencing, should be most informative.

Arabidopsis↗

PubMed1995

Mechanisms of drought response in Thuja occidentalis L. II. Post-conditioning water stress and stress relief.

We examined the extent of osmotic adjustment and the changes in relative water content (RWC) and transpiration rate (i.e., relative stomatal function) that occur in water-deficit-conditioned 6-year-old Thuja occidentalis L. (eastern white cedar) trees in response to a severe drought. Trees conditioned by successive cycles of mild or moderate nonlethal water stress (conditioning) and nonconditioned trees were exposed to drought (i.e., -2.0 MPa predawn water potential) to determine if water deficit conditioning enhanced tolerance to further drought stress. Following drought, all trees were well watered for 11 days to evaluate how quickly osmotic potential, RWC and transpiration rate returned to preconditioning values. Both nonconditioned trees and mildly conditioned trees exhibited similar responses to drought, whereas moderately conditioned trees maintained higher water potentials and transpiration rates were 38% lower. Both conditioned and nonconditioned trees exhibited a similar degree of osmotic adjustment (-0.39 MPa) in response to drought relative to the well-watered control trees. The well-watered control trees, nonconditioned trees and mildly conditioned trees had similar leaf RWCs that were about 3% lower than those of the moderately conditioned trees. Following the 11-day stress relief, there were no significant differences in osmotic potential between the well-watered control trees and any of the drought-treated trees. Daily transpiration rates and water potential integrals (WPI) of all drought-treated trees approached those of the well-watered control trees during the stress relief period. However, the relationship between cumulative transpiration and WPI showed that previous exposure to drought stress reduced transpiration rates. Leaf RWC of the moderately conditioned trees remained slightly higher than that of the nonconditioned and mildly conditioned trees.

Journal Article↗

PubMed1997

Nutrition, xylem cavitation and drought resistance in hybrid poplar.

Effects of mineral nutrition on susceptibility to cavitation were examined in four hybrid poplar clones. Two drought-sensitive and two drought-resistant hybrid clones of black cottonwood (Populus trichocarpa Torr. & Gray) and eastern cottonwood (P. deltoides Bartr.) were grown at three concentrations of nitrogen (N) applied factorially with two concentrations of phosphorus (P) in a greenhouse, and subjected to varying degrees of drought stress before measurement of cavitation and of anatomical features that might affect cavitation. Mean vessel pit pore diameters were 0.132 micro m at low P, and 0.074 micro m at high P, but no other significant effects of mineral nutrition on vessel dimensions were observed. Vessel diameter and specific conductivity were greater in the drought-resistant clones than in the drought-susceptible clones. Drought-resistant clones did not reach such low water potentials as drought-sensitive clones during the cavitation induction experiments, suggesting better stomatal and cuticular control of water loss. Scanning electron microscope observations showed less damage to pit membranes, also suggesting greater membrane strength in drought-resistant clones than in drought-sensitive clones. High concentrations of N increased cavitation, whereas high concentrations of P decreased cavitation as measured by both hydraulic flow apparatus and dye perfusion techniques. For one test, cavitation was 48% at high N and low P, but only 28% at high N and high P. We consider that N fertilization may make poplars more susceptible to cavitation on dry sites, but P fertilization may reduce this effect.

Journal Article↗

PubMed2004

Responses to water stress in two Eucalyptus globulus clones differing in drought tolerance.

We evaluated drought resistance mechanisms in a drought-tolerant clone (CN5) and a drought-sensitive clone (ST51) of Eucalyptus globulus Labill. based on the responses to drought of some physiological, biophysical and morphological characteristics of container-grown plants, with particular emphasis on root growth and hydraulic properties. Water loss in excess of that supplied to the containers led to a general decrease in growth and significant reductions in leaf area ratio, specific leaf area and leaf-to-root area ratio. Root hydraulic conductance and leaf-specific hydraulic conductance decreased as water stress became more severe. During the experiment, the drought-resistant CN5 clone maintained higher leaf water status (higher predawn and midday leaf water potentials), sustained a higher growth rate (new leaf area expansion and root growth) and displayed greater carbon allocation to the root system and lower leaf-to-root area ratio than the drought-sensitive ST51 clone. Clone CN5 possessed higher stomatal conductances at moderate stress as well as higher hydraulic conductances than Clone ST51. Differences in the response to drought in root biomass, coupled with changes in hydraulic properties, accounted for the clonal differences in drought tolerance, allowing Clone CN5 to balance transpiration and water absorption during drought treatment and thereby prolong the period of active carbon assimilation.

Dehydration↗

PubMed1990

Adaptations and responses to drought in Quercus species of North America.

Most North American oaks (Quercus spp.) are adapted to drought-prone sites by an ability either to avoid, or to tolerate, water stress, or both. Generally, they have deep-penetrating root systems, enabling them to maintain relatively high predawn water potentials during drought. Oaks have thick leaves and some have relatively small stomata, both characteristics that favor high water use efficiency. However, some species, from warm regions, have large stomatal pores. The rapid evaporative cooling made possible by large stomata, may be an adaptation to high temperature. Some southeastern species display leaf curling during drought, and Q. douglasii a native of California is drought deciduous. Oaks have a ring-porous xylem anatomy, allowing rapid sap movement in large diameter, early-wood vessels when soil water is plentiful, and slower, but sustained, water movement in narrower, late-wood vessels, which are more resistant to cavitation, during drought. Oaks frequently maintain a higher rate of photosynthesis at low leaf water potentials and high vapor pressure deficits than co-occurring species of other genera. An exception is Quercus rubra, which is generally restricted to relatively mesic sites. During drought, many oak species, especially those native to arid regions, undergo changes in tissue osmotic potential. However, it remains to be shown whether such changes are phenological or drought induced. Reported values for bulk modulus of elasticity vary widely among species and studies, and have been observed to both increase and decrease during drought in a way that is unrelated to region or to changes in predawn water potential or osmotic potential. Diurnal leaf water potential during drought is probably a poor indicator of differences among oak species in gas exchange rate, because of interspecific variation in desiccation avoidance and tolerance.

Journal Article↗

PubMed2004

Quantitative trait loci associated with drought tolerance at reproductive stage in rice.

Drought is a major constraint to rice (Oryza sativa) yield and its stability in rainfed and poorly irrigated environments. Identifying genomic regions influencing the response of yield and its components to water deficits will aid in our understanding of the genetics of drought tolerance and development of more drought tolerant cultivars. Quantitative trait loci (QTL) for grain yield and its components and other agronomic traits were identified using a subset of 154 doubled haploid lines derived from a cross between two rice cultivars, CT9993-510 to 1-M and IR62266-42 to 6-2. Drought stress treatments were managed by use of a line source sprinkler irrigation system, which provided a linearly decreasing level of irrigation coinciding with the sensitive reproductive growth stages. The research was conducted at the Ubon Rice Research Center, Ubon, Thailand. A total of 77 QTL were identified for grain yield and its components under varying levels of water stress. Out of the total of 77 QTL, the number of QTL per trait were: 7-grain yield (GY); 8-biological yield (BY); 6-harvest index (HI); 5-d to flowering after initiation of irrigation gradient (DFAIG); 10-total spikelet number (TSN); 7-percent spikelet sterility (PSS); 23-panicle number (PN); and 11-plant height (PH). The phenotypic variation explained by individual QTL ranged from 7.5% to 55.7%. Under well-watered conditions, we observed a high genetic association for BY, HI, DFAIG, PSS, TSN, PH, and GY. However, only BY and HI were found to be significantly associated with GY under drought treatments. QTL flanked by markers RG104 to RM231, EMP2_2 to RM127, and G2132 to RZ598 on chromosomes 3, 4, and 8 were associated with GY, HI, DFAIG, BY, PSS, and PN under drought treatments. The aggregate effects of these QTL on chromosomes 3, 4, and 8 resulted in higher grain yield. These QTL will be useful for rainfed rice improvement, and will also contribute to our understanding of the genetic control of GY under drought conditions at the sensitive reproductive stage. Close linkage or pleiotropy may be responsible for the coincidence of QTL detected in this experiment. Digenic interactions between QTL main effects for GY, BY, HI, and PSS were observed under irrigation treatments. Most (but not all) DH lines have the same response in measure of productivity when the intensity of water deficit was increased, but no QTL by irrigation treatment interaction was detected. The identification of genomic regions associated with GY and its components under drought stress will be useful for marker-based approaches to improve GY and its stability for farmers in drought-prone rice environments.

Adaptation, Physiological↗

PubMed1994

Drought Rhizogenesis in Arabidopsis thaliana (Differential Responses of Hormonal Mutants).

Drought rhizogenesis is an adaptive strategy that occurs during progressive drought stress and is characterized in the Brassicaceae and related families by the formation of short, tuberized, hairless roots. These roots are capable of withstanding a prolonged drought period and give rise to a new functional root system upon rehydration. The kinetics of drought rhizogenesis during progressive water shortage was analyzed in the Arabidopsis thaliana wild-type ecotypes Landsberg erecta and Columbia. In both genotypes, this response started from a similar threshold of soil humidity (about 2%). The intensity of drought rhizogenesis was compared in various A. thaliana hormonal mutants. The wild-type lines and most of the mutants achieved a similiar drought rhizogenetic index (DRI), defined as the maximum number of short roots produced per mg of root biomass, after progressive drought stress. However, this DRI was dramatically reduced in the abscisic acid (ABA)-deficient aba, ABA-insensitive abi1-1, and auxin-resistant axr1-3 mutants. These data indicate that endogenous ABA and auxin play a promotive role in drought rhizogenesis. The DRI was highly increased in the gibberellin (GA) biosynthetic mutant ga5, suggesting that some GAs might also participate in this process. The possible role and identity of the GA species involved is discussed in view of the unaltered DRI values of the ga2, ga3, and ga4 mutants. The present analysis also allowed further discrimination among the various ABA-insensitive (abi1 versus abi2 and abi3) and auxin-resistant (axr1 versus aux1) mutants tested. In particular, drought rhizogenesis is the first physiological response shown to be differentially affected by the abi1-1 and abi2-1 mutations.

Journal Article↗

PubMed1987

Drought Stress and Elevated CO(2) Effects on Soybean Ribulose Bisphosphate Carboxylase Activity and Canopy Photosynthetic Rates.

Soybean (Glycine max [L.] cv Bragg) was grown at 330 or 660 microliters CO(2) per liter in outdoor, controlled-environment chambers. When the plants were 50 days old, drought stress was imposed by gradually reducing irrigation each evening so that plants wilted earlier each succeeding day. On the ninth day, as the pots ran out of water CO(2) exchange rate (CER) decreased rapidly to near zero for the remainder of the day. Both CO(2)-enrichment and drought stress reduced the total (HCO(3) (-)/Mg(2+)-activated) extractable ribulose-1,5-bisphosphate carboxylase (RuBPCase) activity, as expressed on a chlorophyll basis. In addition, drought stress when canopy CER values and leaf water potentials were lowest, reduced the initial (nonactivated) RuBPCase activity by 50% compared to the corresponding unstressed treatments. This suggests that moderate to severe drought stress reduces the in vivo activation state of RuBPCase, as well as lowers the total activity. It is hypothesized that stromal acidification under drought stress causes the lowered initial RuBPCase activities. The K(m)(CO(2)) values of activated RuBPCase from stressed and unstressed plants were similar; 15.0 and 12.6 micromolar, respectively. RuBP levels were 10 to 30% lower in drought stressed as compared to unstressed treatments. However, RuBP levels increased from near zero at night to around 150 to 200 nanomoles per milligram chlorophyll during the day, even as water potentials and canopy CERs decreased. This suggests that the rapid decline in canopy CER cannot be attributed to drought stress induced limitations in the RuBP regeneration capability. Thus, in soybean leaves, a nonstomatal limitation of leaf photosynthesis under drought stress conditions appears due, in part, to a reduction of the in vivo activity of RuBPCase. Because initial RuBPCase activities were not reduced as much as canopy CER values, this enzymic effect does not explain entirely the response of soybean photosynthesis to drought stress.

Journal Article↗

PubMed1991

The synergistic effect of drought and light stresses in sorghum and pearl millet.

The effects of drought stress and high irradiance and their combination were studied under laboratory conditions using young plants of a very drought-resistant variety, ICMH 451, of pearl millet (Pennisetum glaucum) and three varieties of sorghum (Sorghum bicolor)-one drought-resistant from India, one drought-tolerant from Texas, and one drought-sensitive variety from France. CO(2) assimilation rates and photosystem II fluorescence in leaves were analyzed in parallel with photosynthetic electron transport, photosystem II fluorescence, and chlorophyll-protein composition in chloroplasts isolated from these leaves. High irradiance slightly increased CO(2) assimilation rates and electron transport activities of irrigated plants but not fluorescence. Drought stress (less than -1 megapascal) decreased CO(2) assimilation rates, fluorescence, and electron transport. Under the combined effects of drought stress and high irradiance, CO(2) assimilation rates and fluorescence were severely inhibited in leaves, as were the photosynthetic electron transport activities and fluorescence in chloroplasts (but not photosystem I activity). The synergistic or distinctive effect of drought and high irradiance is discussed. The experiments with pearl millet and three varieties of sorghum showed that different responses of plants to drought and light stresses can be monitored by plant physiological and biochemical techniques. Some of these techniques may have a potential for selection of stress-resistant varieties using seedlings.

Journal Article↗

PubMed2006

Income breeding allows an aquatic snake Seminatrix pygaea to reproduce normally following prolonged drought-induced aestivation.

1. Capital breeding is an ideal reproductive strategy for many ectotherms because it provides a disassociation between feeding and reproduction, a necessary requirement for animals that become anorexic during pregnancy. Among ectotherms, some viviparous snakes (e.g. Viperidae) exemplify the capital breeding strategy because many species (i) do not feed during pregnancy due to behavioural conflicts between reproduction and foraging, and (ii) take more than one season to accumulate sufficient energetic stores for reproduction. 2. Isolated wetlands often exhibit extreme annual fluctuations in environmental conditions with prolonged droughts periodically leaving wetlands completely dry and devoid of prey. Following droughts, however, wetlands can be extremely productive, rendering prey resources virtually unlimited for some species. 3. This study examines drought survival strategy and reproductive ecology of a small aquatic snake Seminatrix pygaea (Cope) in an isolated wetland. Seminatrix pygaea are atypical from most sympatric snake species in that (i) their small body size, reliance on aquatic prey, and high rates of evaporative water loss make them ill-suited to overland movement, and (ii) they may not be subject to costs typically associated with feeding during pregnancy. 4. We hypothesized that S. pygaea would survive periodic multiyear droughts by aestivating within the dried wetland, a survival strategy heretofore undocumented in snakes. Further, we hypothesized that if S. pygaea rely on 'typical' snake reproductive strategies of 'adaptive anorexia' and capital breeding, reproductive output would be reduced in the first wet year following drought. 5. By encircling a 10-ha wetland with a continuous drift fence before it refilled we were able to demonstrate that S. pygaea were present within the dried wetland prior to the onset of spring rains that refilled the wetland in 2003. Our results suggest that S. pygaea are capable of surviving multiyear droughts by aestivating within the dried wetland. 6. Despite having presumably depleted energy reserves during the drought, S. pygaea reproduced with the same frequency and fecundity during the first season following refilling of the wetland as in pre-drought years. 7. The ability of S. pygaea to rebound rapidly from the stresses of prolonged drought is due in part to their reproductive ecology. Seminatrix pygaea readily feed throughout pregnancy and consequently can rapidly translate high prey abundances into reproductive output through income breeding.

Animals↗

PubMed2005

Molecular tailoring of farnesylation for plant drought tolerance and yield protection.

Protecting crop yield under drought stress is a major challenge for modern agriculture. One biotechnological target for improving plant drought tolerance is the genetic manipulation of the stress response to the hormone abscisic acid (ABA). Previous genetic studies have implicated the involvement of the beta-subunit of Arabidopsis farnesyltransferase (ERA1) in the regulation of ABA sensing and drought tolerance. Here we show that molecular manipulation of protein farnesylation in Arabidopsis, through downregulation of either the alpha- or beta-subunit of farnesyltransferase enhances the plant's response to ABA and drought tolerance. To test the effectiveness of tailoring farnesylation in a crop plant, transgenic Brassica napus carrying an ERA1 antisense construct driven by a drought-inducible rd29A promoter was examined. In comparison with the non-transgenic control, transgenic canola showed enhanced ABA sensitivity, as well as significant reduction in stomatal conductance and water transpiration under drought stress conditions. The antisense downregulation of canola farnesyltransferase for drought tolerance is a conditional and reversible process, which depends on the amount of available water in the soil. Furthermore, transgenic plants were more resistant to water deficit-induced seed abortion during flowering. Results from three consecutive years of field trial studies suggest that with adequate water, transgenic canola plants produced the same amount of seed as the parental control. However, under moderate drought stress conditions at flowering, the seed yields of transgenic canola were significantly higher than the control. Using protein farnesyltransferase as an effective target, these results represent a successful demonstration of engineered drought tolerance and yield protection in a crop plant under laboratory and field conditions.

Abscisic Acid↗

PubMed2001

Differential stress responses of antioxidative systems to drought in pendunculate oak (Quercus robur) and maritime pine (Pinus pinaster) grown under high CO(2) concentrations.

Maritime pine (Pinus pinaster), a drought-avoiding species, contained 2--4-fold lower activities of superoxide dismutase, ascorbate peroxidase, catalase, dehydroascorbate reductase, and glutathione reductase than pendunculate oak (Quercus robur), a drought-tolerant species. The levels of ascorbate, monodehydroascorbate radical reductase activity, and glutathione in pine needles were similar to those in oak leaves. In both species the development of drought stress, characterized by decreasing predawn water potentials, caused gradual reductions in antioxidant protection, increased lipid peroxidation, increased oxidation of ascorbate and glutathione and in pine also significant loss in soluble proteins and carotenoids. These results support the idea that increased drought-tolerance in oak as compared with pine is related to increased biochemical protection at the tissue level. To test the hypothesis that elevated CO(2) ameliorated drought-induced injury, young oak and pine trees acclimated to high CO(2) were subjected to drought stress. Analysis of plots of enzymatic activities and metabolites against predawn water potentials revealed that the drought stress-induced decreases in antioxidant protection and increases in lipid peroxidation were dampened at high CO(2). In pine, protein and pigment degradation were also slowed down. At high CO(2), superoxide dismutase activities increased transiently in drought-stressed trees, but collapsed in pine faster than in oak. These observations suggest that the alleviation of drought-induced injury under elevated CO(2) is related to a higher stability of antioxidative enzymes and an increased responsiveness of SOD to stressful conditions. This ameliorating mechanism existed independently from the effects of elevated CO(2) on plant water relations and is limited within a species-specific metabolic window.

Antioxidants↗

PubMed2003

[Eco-physiological responses of Picea mongolica ecotypes to drought stress].

The seedlings of different Picea mongolica ecotypes were treated with drought stress, and their height growth, MDA, proline, and chlorophyll content were investigated. The results showed that the height growth was obviously reduced by drought stress. With sufficient water supply, the height growth of f. viridis W. D. Xu f. nov Picea mongolica was rapid and obviously better than that of f. purpurea W. D. Xu f. nov Picea mongolica, but was obviously reduced by intense drought stress. Furthermore, drought stress shortened the annual growth period of Picea mongolica, and made its terminal bud formation more than one month earlier increased in both needles and roots, but was higher in needle than in root. The MDA content was higher in Picea mongolica than in f. viridis W. D. Xu f. nov Piburcea mongolica, and the proline content in needles was increased with increasing drought stress, but in roots, the proline content was higher in f. viridis W. D. Xu f. nov Picea mongolica than in f. purpurea W. D. Xu f. nov Picea mongolica and f. rubra W. D. Xu f. nov Picea mongolica. The latter 2 forms showed a similar trend in chlorophyll content. Their chlorophyll a, chlorophyll b and total chlorophyll contents increased at the beginning of drought treatment, and then decreased with increasing drought stress. The chlorophyll content of f. viridis W. D. Xu f. nov Picea mongolica decreased with drought stress. The ratio of chlorophyll a/b decreased from maximum to minimum in f. viridis W. D. Xu f. nov Picea mongolica, but decreased in a relative small extent in f. purpurea W. D. Xu f. nov. It's proved that f. purpurea W. D. Xu f. nov Picea mongolica had a larger drought-resistance capacity than f. viridis W. D. Xu f. nov, and f. rubra W. D. Xu f. nov was a typical transitional ecotype from f. purpurea W. D. Xu f. nov to f. viridis W. D. Xu f. nov.

Chlorophyll↗

PubMed2003

Effects of drought stress on legume symbiotic nitrogen fixation: physiological mechanisms.

Drought stress is one of the major factors affecting nitrogen fixation by legume-rhizobium symbiosis. Several mechanisms have been previously reported to be involved in the physiological response of symbiotic nitrogen fixation to drought stress, i.e. carbon shortage and nodule carbon metabolism, oxygen limitation, and feedback regulation by the accumulation of N fixation products. The carbon shortage hypothesis was previously investigated by studying the combined effects of CO2 enrichment and water deficits on nodulation and N2 fixation in soybean. Under drought, in a genotype with drought tolerant N2 fixation, approximately four times the amount of 14C was allocated to nodules compared to a drought sensitive genotype. It was found that an important effect of CO2 enrichment of soybean under drought was an enhancement of photo assimilation, an increased partitioning of carbon to nodules, whose main effect was to sustain nodule growth, which helped sustain N2 rates under soil water deficits. The interaction of nodule permeability to O2 and drought stress with N2 fixation was examined in soybean nodules and led to the overall conclusion that O2 limitation seems to be involved only in the initial stages of water deficit stresses in decreasing nodule activity. The involvement of ureides in the drought response of N2 fixation was initially suspected by an increased ureide concentration in shoots and nodules under drought leading to a negative feedback response between ureides and nodule activity. Direct evidence for inhibition of nitrogenase activity by its products, ureides and amides, supported this hypothesis. The overall conclusion was that all three physiological mechanisms are important in understanding the regulation of N2 fixation and its response of to soil drying.

Carbon Dioxide↗

PubMed2005

[Effects of nitrogen supply on flag leaf photosynthesis and grain starch accumulation of wheat from its anthesis to maturity under drought or waterlogging].

In this paper, a cement pool culture experiment with three water treatments (waterlogging, drought, and moderate water supply) and two nitrogen levels (120 and 240 kg x hm(-2)) was conducted to study the effects of nitrogen supply on the flag leaf photosynthesis and grain starch accumulation of two wheat varieties from anthesis to maturity under soil drought and waterlogging. In comparing with moderate water supply, soil drought and waterlogging reduced the photosynthesis rate (Pn) and SPAD of flag leaf and dry matter accumulation. Nitrogen supply under drought increased Pn and SPAD, while that under waterlogging was in adverse. The total soluble sugar content in grain was reduced under both drought and waterlogging, while that in leaf was decreased under waterlogging but increased under drought. Under waterlogging, increasing nitrogen application rate reduced starch accumulation. The unit grain weight and the yields of grain and starch were reduced under both drought and waterlogging, but nitrogen application favored them under drought while in adverse under waterlogging. It was indicated that both leaf photosynthesis and grain starch accumulation could be regulated by nitrogen supply under stress of soil drought or waterlogging from anthesis to maturity of wheat.

Edible Grain↗