Differences In Drought Tolerance Research Articles

An analysis of physiological index of differences in drought tolerance of tomato rootstock seedlings

Drought is one of the most limiting factors for plant growth and development. In this study, experiments were carried out on five tomato rootstocks were subjected to water withdrawal and re-watering. Two RKN (root-knot nematodes)-and drought-dual resistant rootstocks were identified according to phenotype, physiological and molecular indexes such as the leaf relative water content (LRWC), electrolyte leakage (EL), water loss of the leaf, proline content, and increased activities of antioxidant enzymes, including peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and the transcript levels of drought stress marker genes. Further, we preliminarily investigated the mechanism underlying improved drought tolerance arising from grafting. These results will promote the application of these rootstocks in tomato production and provide new information on the mechanism of tomato grafting.

Survival is not enough: The effects of microclimate on the growth and health of three common urban tree species in San Francisco, California

Urban forest managers must balance social, economic, and ecological goals through tree species selection and planting location. Ornamental trees are often popular in tree planting programs for their aesthetic benefits, but studies find that they have lower survivability and growth compared to larger shade trees. To maximize ecosystem services within these aesthetic preferences, it is important to select species carefully based on their ability to grow in each particular climate. However, little locality-specific and species-specific data exist on urban trees in many regions. This study examines the growth, survival, and vigor of three common ornamental street trees in San Francisco’s three different microclimate zones after over 16 years since planting. While we found over 70% survival for all three species throughout the city, there were significant differences in health and vigor among microclimates for each species, likely due to differences in drought-tolerance. While Arbutus had the greatest proportion of healthy trees in the Fog Belt and Sun Belt zones, Prunus cerasifera had the greatest proportion in the Sun Belt, and Prunus serrulata had the greatest proportions in the Transition and the Sun Belt zones. This species-specific and climate-specific information will better equip urban foresters to target both planting and tree-care of these popular species appropriately to maximize the benefits provided by these street trees while still maintaining a diverse canopy. Finally, we argue that simple survival calculations can mask more complex differences in the health and ability of different urban tree species to provide ecosystem services.

Physiological responses and tolerance to drought stress of different watermelon genotypes.

With the continuous drought stress treatment to 12 pot-grown watermelon genotypes originated from different regions, the influence of drought stress on plant height, root length, fresh mass and dry mass was studied, and the physiological responses of these genotypes to drought stress were compared. Drought resistance of these watermelon genotypes was preliminarily determined according to the drought injury, and then confirmed by membership function evaluation method. We found that the watermelon genotypes exhibited great difference in drought tolerance based on the occurrence of drought injury and the degree of injury severity. Drought stress reduced plant height, shoot- and root- fresh mass as well as shoot- and root- dry mass, while increased the root/shoot ratio for most genotypes; but for root length and root dry mass, it had both positive and negative effects depending on the tested genotype. Compared with the control, all drought-treated watermelon genotypes exhibited a decline in leaf relative water content and chlorophyll content, as well as increases in MDA, H2O2, O2-· and proline contents. Different watermelon genotypes displayed diversity in soluble protein content and antioxidant enzyme activity. Our results showed that three wild watermelon genotypes including M20, Y-2, and KY-3 were drought tolerant while Y34, 04-1-2 and Golden Girl were drought sensitive, and the rest genotypes were among the medium.

Drought Tolerance Is Correlated with the Activity of Antioxidant Enzymes in Cerasus humilis Seedlings.

Cerasus humilis, grown in the northern areas of China, may experience water deficit during their life cycle, which induces oxidative stress. Our present study was conducted to evaluate the role of oxidative stress management in the leaves of two C. humilis genotypes, HR (drought resistant) and ND4 (drought susceptible), when subjected to a long-term soil drought (WS). The HR plants maintained lower membrane injury due to low ROS and MDA accumulation compared to ND4 plants during a long-term WS. This is likely attributed to global increase in the activities of superoxide dismutase (SOD) isoenzymes and enzymes of the ascorbate-glutathione (AsA-GSH) cycle and maintenance of ascorbate (AsA) levels. Consistent closely with enzymes activities, the expression of cytosolic ascorbate peroxidase (cAPX) and dehydroascorbate reductase (DHAR) followed a significant upregulation, indicating that they were regulated at the transcriptional level for HR plants exposed to WS. In contrast, ND4 plants exhibited high ROS levels and poor antioxidant enzyme response, leading to enhanced membrane damage during WS conditions. The present study shows that genotypic differences in drought tolerance could be likely attributed to the ability of C. humilis plants to induce antioxidant defense under drought conditions.

Osmoregulants Involved in Osmotic Adjustment for Differential Drought Tolerance in Different Bentgrass Genotypes

Compatible solute accumulation regulating osmotic adjustment (OA) is associated with drought tolerance. The objectives of this study were to examine genetic variations in OA among a diverse group of bentgrass (Agrostis sp.) genotypes or lines with differential drought tolerance, and determine major types of organic osmoregulants contributing to OA and accounting for the genetic variations in drought tolerance. A wild type cultivar of creeping bentgrass [Agrostis stolonifera (Penncross)], a transgenic line of creeping bentgrass (SAGIPT41), and four hybrid bentgrass lines [Agrostis capillaris × Agrostis stolonifera (ColxCr14, ColxCr190, ColxCr481, and ColxCr679)] were exposed to drought stress by withholding irrigation for 17 days in growth chambers. Among genotypes, ColxCr14, ColxCr190, and SAGIPT41 showed superior drought tolerance, as manifested by higher turf quality (TQ) and leaf relative water content (RWC), as well as OA than ‘Penncross’, ColxCr679, and ColxCr481 under drought stress. SAGIPT41 leaves accumulated greater content of soluble sugars (glucose, sucrose, and fructose), proline, glycine betaine (GB), and spermine; ColxCr190 had higher content of soluble sugars and spermidine; and ColxCr14 accumulated more soluble sugars and GB, compared with the three drought-sensitive genotypes. Soluble sugars were predominant contributors to OA, followed by GB and proline, with all three forms of polyamine (PA) as minor contributors in bentgrass genotypes. The osmolytes highly correlated to OA and superior drought tolerance could be used as biomarkers to select for drought-tolerant germplasm of bentgrass and other cool-season turfgrass species.

Metabolites and hormones are involved in the intraspecific variability of drought hardening in radiata pine

Studies of metabolic and physiological bases of plant tolerance and hardening against drought are essential to improve genetic breeding programs, especially in productive species such as Pinus radiata. The exposure to different drought cycles is a highly effective tool that improves plant conditioning, but limited information is available about the mechanisms that modulate this process. To clarify this issue, six P. radiata breeds with well-known differences in drought tolerance were analyzed after two consecutive drought cycles. Survival rate, concentration of several metabolites such as free soluble amino acids and polyamines, and main plant hormones varied between them after drought hardening, while relative growth ratio and water potential at both predawn and dawn did not. Hardening induced a strong increase in total soluble amino acids in all breeds, accumulating mainly those implicated in the glutamate metabolism (GM), especially l-proline, in the most tolerant breeds. Other amino acids from GM such as γ-aminobutyric acid (GABA) and l-arginine (Arg) were also strongly increased. GABA pathway could improve the response against drought, whereas Arg acts as precursor for the synthesis of spermidine. This polyamine showed a positive relationship with the survival capacity, probably due to its role as antioxidant under stress conditions. Finally, drought hardening also induced changes in phytohormone content, showing each breed a different profile. Although all of them accumulated indole-3-acetic acid and jasmonic acid and reduced zeatin content in needles, significant differences were observed regarding abscisic acid, salicylic acid and mainly zeatin riboside. These results confirm that hardening is not only species-dependent but also an intraspecific processes controlled through metabolite changes.

Phenotypic and Genotypic Diversity for Drought Tolerance among and within Perennial Ryegrass Accessions

Perennial ryegrass (Lolium perenne L.) is a popular cool-season forage and turfgrass in temperate regions. Due to its self-incompatible and out-crossing nature, perennial ryegrass may show a high degree of heterozygosity. Perennial ryegrass generally is susceptible to drought stress, but variations of drought response of individual genotypes within a particular accession or cultivar are not well understood. The objective of this study was to characterize phenotypic diversity of drought tolerance within and among accessions in relation to genetic diversity in perennial ryegrass. Five individual genotypes from each of six accessions varying in origin and growth habits were subjected to drought stress in a greenhouse. Leaf wilting, plant height, chlorophyll fluorescence (Fv/Fm) and leaf water content (LWC) differed significantly among accessions as well as among genotypes within each accession under well-watered control and drought stress conditions. Fv/Fm was highly correlated with LWC under drought stress. Genetic diversity among and within accessions were identified by using previously characterized 23 simple sequence repeat markers. Across accessions, the mean major allele frequency, gene diversity, and heterozygosity values were 0.66, 0.43, and 0.66, respectively. Accessions with closer genetic distance generally had similar drought responses, while accessions with greater genetic distance showed distinct drought tolerance. Significant differences in drought tolerance among and within accessions, especially for individual genotypes within one accession, indicated that variations of drought response could be used for enhancing breeding programs and studying molecular mechanisms of stress tolerance in perennial ryegrass.

Identification of novel drought-responsive microRNAs and trans-acting siRNAs from Sorghum bicolor (L.) Moench by high-throughput sequencing analysis.

Small non-coding RNAs (sRNAs) namely microRNAs (miRNAs) and trans-acting small interfering RNAs (tasi-RNAs) play a crucial role in post-transcriptional regulation of gene expression and thus the control plant development and stress responses. In order to identify drought-responsive miRNAs and tasi-RNAs in sorghum, we constructed small RNA libraries from a drought tolerant (M35-1) and susceptible (C43) sorghum genotypes grown under control and drought stress conditions, and sequenced by Illumina Genome Analyzer IIx. Ninety seven conserved and 526 novel miRNAs representing 472 unique miRNA families were identified from sorghum. Ninety-six unique miRNAs were found to be regulated by drought stress, of which 32 were up- and 49 were down-regulated (fold change ≥ 2 or ≤ −2) at least in one genotype, while the remaining 15 miRNAs showed contrasting drought-regulated expression pattern between genotypes. A maximum of 17 and 18 miRNAs was differentially regulated under drought stress condition in the sensitive and tolerant genotypes, respectively. These results suggest that genotype dependent stress responsive regulation of miRNAs may contribute, at least in part, to the differential drought tolerance of sorghum genotypes. We also identified two miR390-directed TAS3 gene homologs and the auxin response factors as tasi-RNA targets. We predicted more than 1300 unique target genes for the novel and conserved miRNAs. These target genes were predicted to be involved in different cellular, metabolic, response to stimulus, biological regulation, and developmental processes. Genome-wide identification of stress-responsive miRNAs, tasi-RNAs and their targets identified in this study will be useful in unraveling the molecular mechanisms underlying drought stress responses and genetic improvement of biomass production and stress tolerance in sorghum.

Drought sensitivity predicts habitat size sensitivity in an aquatic ecosystem.

Species and trophic richness often increase with habitat size. Although many ecological processes have been evoked to explain both patterns, the environmental stress associated with small habitats has rarely been considered. We propose that larger habitats may be species rich simply because their environmental conditions are within the fundamental niche of more species; larger habitats may also have more trophic levels if traits of predators render them vulnerable to environmental stress. We test this hypothesis using the aquatic insect larvae in water-filled bromeliads. In bromeliads, the probability of desiccation is greatest in small plants. For the 10 most common bromeliad insect taxa, we ask whether differences in drought tolerance and regional abundances between taxa predict community and trophic composition over a gradient of bromeliad size. First, we used bromeliad survey data to calculate the mean habitat size of occurrence of each taxon. Comparing the observed mean habitat size of occurrence to that expected from random species assembly based on differences in their regional abundances allowed us to obtain habitat size sensitivity indices (as Z scores) for the various insect taxa. Second, we obtained drought sensitivity indices by subjecting individual insects to drought and measuring the effects on relative growth rates in a mesocosm experiment. We found that drought sensitivity strongly, predicts habitat size sensitivity in bromeliad insects. However, an increase in trophic richness with habitat size could not be explained by an increased sensitivity of predators to drought, but rather by sampling effects, as predators were rare compared to lower trophic levels. This finding suggests that physiological tolerance to environmental stress can be relevant in explaining the universal increase in species with habitat size.

Modeling Response of Warm‐Season Turfgrass to Drought and Irrigation

When droughts occur, restrictions on outdoor water use are a frequently used tactic for reducing demand but are not always as effective as desired and can have negative impacts on homeowners and businesses. Our objective was to develop a simulation model for use in comparing irrigation strategies in terms of water usage and changes in turfgrass quality under varying levels of water restriction. Based on data from several experiments, we have developed a model for St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] and bermudagrass [Cynodon dactylon (L.) Pers.] that calculates a turfgrass drought index and a turfgrass quality index (TQI) on a daily basis. Turfgrass water demand is modeled as a function of TQI and reference evapotranspiration. Actual turf water uptake depends on plant‐available soil water as well as plant demand. Available soil water in the root zone is divided into two pools: an easily available pool and a less readily available pool. Turfgrass quality can increase when there is no drought stress and decline whenever drought stress exceeds a cultivar‐specific threshold. We used the generalized likelihood uncertainty estimation method to estimate five genetic coefficients for two cultivars of each species. The model was highly successful in predicting the observed values of TQI. Except for a few sample dates, simulated TQI was within the 95% confidence interval of the mean observed TQI. The model appears to respond accurately to both drought and irrigation and to capture species and cultivar differences in drought tolerance.

Aspect reduces soil moisture and tree cover, but not nitrogen mineralization or grass cover, in semiarid pinyon-juniper woodlands of the Southwestern United States

Global climate change is expected to increase the aridity of semiarid landscapes by increasing heat stress and decreasing soil moisture, negatively impacting plant survival, growth, and reproduction and forcing major shifts in plant community composition. To better understand potential vegetation shifts, we investigated how aspect-mediated differences in soil moisture and nitrogen influence tree-grass and tree species coexistence in pinyon-juniper woodlands in the southwestern United States (at the Sevilleta Long Term Ecological Research Station in New Mexico). We measured soil moisture, total mineralized soil nitrogen, grass cover, and woody cover and demography of the two dominant trees—two-needle pinyon pine (Pinus edulis) and one-seeded juniper (Juniperus monosperma)—along 32 transects on north-facing and south-facing slopes. Tree cover was greater on north-facing than on south-facing slopes, reflecting significantly higher soil moisture on northern aspects. Aspect did not affect soil nitrogen or grass cover. Population structure for juniper was influenced by aspect while reproductive output was influenced by aspect in both species, suggesting that differences in drought tolerance between these codominant tree species may be responsible for differences in the utilization of resources in our study area. Our results suggest that soil moisture can affect tree cover and tree-grass coexistence more than does nitrogen. Increasing aridity due to global climate change is likely to decrease woody cover in semiarid landscapes, resulting in systems codominated by grasses and woody species.

Response of leaf water status, stomatal characteristics, photosynthesis and yield in black gram and green gram genotypes to soil water deficit.

Drought is one of the most important abiotic stresses constraining crop productivity worldwide. The objective of the present study was to investigate the differences in drought tolerance at leaf and stomatal level of black gram (genotypes: T9, KU 301, PU 19, USJD 113) and green gram (genotypes: Pratap, SG 21-5, SGC 16, TMB 37). Drought was applied for fifteen consecutive days at flowering stage (35 days after sowing). Mid-day leaf water potential (ΨL), leaf area, photosynthesis rate (PN), leaf chlorophyll, stomatal conductance (gs) and seed yield of drought- treated plants were calculated relative to those of well watered plants. Stomatal characteristics were observed in terms of stomatal frequency (SF) and stomatal aperture size (SA). Among the studied genotypes, T9 (black gram) and Pratap (green gram) proved their better tolerance capacity to drought by maintaining higher leaf area, ΨL, PN, leaf chlorophyll, gs and SA which contributed to better seed yield. Between the two crops, green gram appeared to be affected to a greater extent, as it experienced higher reduction in yield than black gram. A highly significant positive correlation (level 0.01) of seed yield was obtained with leaf area, ΨL, PN, leaf chlorophyll, gs and SA, whereas SF was found to be poorly correlated with seed yield.

Drought Tolerance Selection of Sugarbeet Hybrids

Increased water demands and drought have resulted in a need to indentify crop hybrids that are drought tolerant, requiring less irrigation to sustain yields. This study was conducted to assess differences in drought tolerance among a group of genetically diverse sugarbeet hybrids. The study was conducted over three consecutive growing seasons (2008-2010) at the USDA Northwest Irrigation and Soils Research Laboratory in Kimberly, Idaho on a Portneuf silt loam soil (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid). Drought tolerance was evaluated by measuring sucrose yield production of six breeding hybrids of Klein Wanzlebener Saatzucht (KWS SAAT AG) and one commercial hybrid (Betaseed Inc.) under six water input treatments. Hybrid drought tolerance was evaluated by linear regression analysis (slope and intercept) of yield versus water input, calculation of a drought stress index (DSI), and comparison of yield potential under full irrigation. The water input treatments were based on a percentage of estimated crop evapoatransipration (ETc). Water input treatments were 125% ETc (W1), 100% ETc (W2), 75% ETc (W3), 50% ETc (W4), 25% ETc (W5) and rain-fed (W6). Irrigation was applied three times a week to meet the desgnated rate. There were significant differences in overall yield potential and in the sucrose yield response to water among hybrids. Greater drought tolerance or greater difference in sucrose yield between hybrids was seen at the lowest water input treatment (intercept difference). Greater drought tolerance was observed for the KWS-05 hybrids compared to the commercial hybrid. Based on these results there exist genetic diversity among existing sugarbeet breeding hybrids.

Overexpression of AtDREB1D transcription factor improves drought tolerance in soybean.

Drought is one of the major abiotic stresses that affect productivity in soybean (Glycine max L.) Several genes induced by drought stress include functional genes and regulatory transcription factors. The Arabidopsis thaliana DREB1D transcription factor driven by the constitutive and ABA-inducible promoters was introduced into soybean through Agrobacterium tumefaciens-mediated gene transfer. Several transgenic lines were generated and molecular analysis was performed to confirm transgene integration. Transgenic plants with an ABA-inducible promoter showed a 1.5- to two-fold increase of transgene expression under severe stress conditions. Under well-watered conditions, transgenic plants with constitutive and ABA-inducible promoters showed reduced total leaf area and shoot biomass compared to non-transgenic plants. No significant differences in root length or root biomass were observed between transgenic and non-transgenic plants under non-stress conditions. When subjected to gradual water deficit, transgenic plants maintained higher relative water content because the transgenic lines used water more slowly as a result of reduced total leaf area. This caused them to wilt slower than non-transgenic plants. Transgenic plants showed differential drought tolerance responses with a significantly higher survival rate compared to non-transgenic plants when subjected to comparable severe water-deficit conditions. Moreover, the transgenic plants also showed improved drought tolerance by maintaining 17-24 % greater leaf cell membrane stability compared to non-transgenic plants. The results demonstrate the feasibility of engineering soybean for enhanced drought tolerance by expressing stress-responsive genes.

Field Phenotyping of Soybean Roots for Drought Stress Tolerance

Root architecture was determined together with shoot parameters under well watered and drought conditions in the field in three soybean cultivars (A5409RG, Jackson and Prima 2000). Morphology parameters were used to classify the cultivars into different root phenotypes that could be important in conferring drought tolerance traits. A5409RG is a drought-sensitive cultivar with a shallow root phenotype and a root angle of <40°. In contrast, Jackson is a drought-escaping cultivar. It has a deep rooting phenotype with a root angle of >60°. Prima 2000 is an intermediate drought-tolerant cultivar with a root angle of 40°–60°. It has an intermediate root phenotype. Prima 2000 was the best performing cultivar under drought stress, having the greatest shoot biomass and grain yield under limited water availability. It had abundant root nodules even under drought conditions. A positive correlation was observed between nodule size, above-ground biomass and seed yield under well-watered and drought conditions. These findings demonstrate that root system phenotyping using markers that are easy-to-apply under field conditions can be used to determine genotypic differences in drought tolerance in soybean. The strong association between root and nodule parameters and whole plant productivity demonstrates the potential application of simple root phenotypic markers in screening for drought tolerance in soybean.

Nitric oxide increases tolerance responses to moderate water deficit in leaves of Phaseolus vulgaris and Vigna unguiculata bean species.

Drought stress is one of the most intensively studied and widespread constraints, and nitric oxide (NO) is a key signaling molecule involved in the mediation of abiotic stresses in plants. We demonstrated that a sprayed solution of NO from donor sodium nitroprusside increased drought stress tolerance responses in both sensitive (Phaseolus vulgaris) and tolerant (Vigna unguiculata) beans. In intact plants subjected to halting irrigation, NO increased the leaf relative water content and stomatal conductance in both species. After cutting leaf discs and washing them, NO induced increased electrolyte leakage, which was more evident in the tolerant species. These leaf discs were then subjected to different water deficits, simulating moderate and severe drought stress conditions through polyethylene glycol solutions. NO supplied at moderate drought stress revealed a reduced membrane injury index in sensitive species. In hydrated discs and at this level of water deficit, NO increased the electron transport rate in both species, and a reduction of these rates was observed at severe stress levels. Taken together, it can be shown that NO has an effective role in ameliorating drought stress effects, activating tolerance responses at moderate water deficit levels and in both bean species which present differential drought tolerance.

Assessment of Triticale (Triticosecale) X Bread Wheat (Triticum Aestivum) Genotypes for Drought Tolerance Based on Morpho-Physiological, Grain Yield and Drought Tolerance Indices Under Non-Irrigated and Irrigated Environments

Wheat being important staple crop urges the need to evaluate and develop new drought-tolerant varieties to sustain its productivity under changing climatic conditions. Therefore, this study was conducted to assess the differential morpho-physiological, grain yield and drought tolerance indices responses of 27 triticale x bread wheat genotypes along with eight checks under non-irrigated and irrigated environments in randomized complete block design with three replications. Data on 12 important morpho-physiological and grain yield related traits along with revealed sufficient variability under two environments. Among various traits magnitude of heritability and genetic advance indicated that selection of flag-leaf area, spikes per plant and 1000-grain weight could respond to higher grain yield under non-irrigated environment. Seedling stage traits viz., germination percentage, root length, shoot length, seedling vigour index (SVI) and germination index (GI) under normal (0 bar) and simulated water stress with Polyethylene glycol at -8 bar indicated greater sensitivity of the genotypes to water stress. Five drought tolerance indices viz.,drought susceptibility index (DSI), tolerance index (TOL), stress tolerance index (STI), yield index (YI) and yield stability index (YSI) were also calculated to identify drought tolerant and stable genotypes based on their yields under two environ- ments. Minimum value of DSI, TOL and yield reduction and maximum value of YSI were in harmony with each other to categorized RL 135-P1 RL 22-144 A, RL-110-1P1, RL 128-1 P1 and RL 118-P1 as top five promising drought tolerant and yield stable genotypes. These genotypes could potentially be utilized for drought tolerance wheat breeding program.

Leaf micromorphology and sugar may contribute to differences in drought tolerance for two apple cultivars

Apple trees (Malus domestica L.) are often exposed to severe water stress in the summertime. We determined how levels of nonstructural carbohydrates (NC) changed in the leaves of two cultivars – drought-tolerant ‘QinGuan’ and drought-sensitive ‘NaganoFuji’ – when plants were subjected for 10 d to a sudden water deficit. Photosynthetic performance was investigated in terms of gas exchange and antioxidant enzyme activity. Two separate irrigation scenarios were tested with one-year-old plants grafted onto Malus hupehensis (Pamp.) Rehd. rootstock: 1) water applied to 75% field capacity (FC) (Control, CK) and 2) irrigation withheld to achieve <75% FC ranging from 30 to 75% (Treatment, T). At Days 0, 1, 2, 4, 6, and 10 of the experiment, we recorded net CO2 assimilation, stomatal conductance, leaf transpiration rates, and intercellular CO2 concentrations. All of those parameters showed decreases in plants from both stress scenarios, although those declines were not as dramatic in ‘QinGuan’. The photosynthetic rate reduced primarily because of stomatal closure. In both cultivars, water stress induced the accumulation of NC, especially sorbitol, suggesting that this polyol has a role in osmoregulation. The rise in sorbitol levels was much steeper in ‘QinGuan’. Likewise, the interaction between superoxide dismutase and peroxidase activities varied between cultivars. In ‘QinGuan’, the malondialdehyde concentration was much lower and more closely correlated with a high Suc/NC ratio when compared with ‘NaganoFuji’. Scanning electron microscopy revealed a drought-resisting apparent structure in ‘QinGuan’. Overall, our results from both external and internal examinations demonstrated that ‘QinGuan’ is more drought-tolerant than ‘NaganoFuji’.

Trade-off between leaf turnover and biochemical responses related to drought tolerance in desert woody plants

We describe differences in leaf photo-protection mechanisms in a group of arid adapted C3 and C4 shrubs that differ in their leaf life-span and compared these mechanisms to known differences in drought tolerance. The experiments were carried out in the field with fourteen woody species native to the Hexi Corridor region, northwestern China. We assessed water status, chlorophyll content, antioxidant enzymes activity, and solute content. We found that differences in photo-protection mechanism among species were not a consequence of differences in photosynthetic pathway, but they were related to leaf life-span. Further, we found evidence that supports the concept of a trade-off between leaf turnover and photo-protective mechanism: species with a longer leaf life-span (leaves with low turnover rate) had higher values of enzymatic (POD and CAT) and no-enzymatic (Chl a, Chl b, Car, and soluble sugars-SS) compounds, than species with a shorter life-span (high turnover rate). These different photoprotective strategies are in accordance with known differences in morphological and physiological leaf attributes that allow for rapid acquisition resources (i.e. acquisitive type) or permit conservation of resources within well protected tissues (i.e. conservative type).

Relationship between Water Use Efficiency and Î"13C Isotope Discrimination of Safflower (Carthamus tinctorius L.) under Drought Stress

Drought stress is one of the most limiting factors in agricultural productivity because of its highly negative effect on photosynthesis and growth of plants. The main objectives of this study were to determine the performance of four selected safflower genotypes (Remzibey, Dincer, Balci and TRE-ASL09/14) against drought stress. The relationship between water use efficiency (WUE) and δ13C (isotope discrimination) was investigated under well watered (60%) and drought stress (30%) irrigation in controlled conditions in a green house. The result showed that drought stress clearly reduced plant biomass, leaf area, leaf number, relative water content (RWC), specific leaf weight (SLW), WUE and δ13C in all genotypes, while chlorophyll increased under drought stress. There were significant differences between performances of all safflower genotypes in terms of response to drought stress. High WUE and low δ13C discrimination under drought stress were inversely associated with a strong regression relationship (R2=0.75). The analysis of δ13C revealed a substantial variation in water use efficiency among the genotypes under drought stress. It was revealed that low δ13C discrimination types had high WUE, RWC and total biomass under drought stress. Thus, the ability of the low δC genotypes (high water use efficiency, WUE) to maintain higher RWC may provide a good indication of the differences in drought tolerance of safflower genotypes differing in δ13C. Overall, on the basis of the consistent percentage reductions in plant heights, total dry weight, leaf area, RWC, WUE and low δ13C, the TRE-ASL09/14 new breeding line was found to be more drought tolerant when compared with the other safflower hybrids under drought stress. As a result of our study it is suggested that there is a strong relationship between WUE and lower δ13C under drought stress, indicating that it may be used as a selection criterion for developing safflower genotypes with drought tolerance