Screening of tall fescue genotypes for relative water content and osmotic potential under drought stress

Background:Tall fescue(Festuca arundinacea Schreb.)is an important coolseason perennial grass.Its persistence and forage yield can be severely affected by drought stresses during the hot,dry summers of the southern USA.Methods:One thousand tall fescue genotypes were evaluated in the greenhouse for high relative water content(RWC)and low cell sap osmotic potential(OP).Fifty contrasting genotypes for the two traits were identified and used in further greenhouse and field studies.These genotypes were also screened with 30%PEG8000.Root and shoot characteristics were studied in 10 genotypes.Results:The genotypes differed for RWC(33.7%–97.3%,mean:79.7%)and had an almost fivefold difference in OP(−0.5 to−2.4 MPa,mean:−1.2 MPa).Significant variation(p<0.001)for the main effects of environment and genotypes was found for RWC and OP.Apart from the greenhouse trial,no correlation was found between RWC and OP,indicating that differences in RWC might have been due to factors other than osmotic adjustment.Genotypes with either long roots or high root weights,and high root/shoot ratios demonstrated high RWC and low OP.Conclusions:Genotypes with consistently high RWC and low OP were identified and used for the development of mapping populations and transcriptome studies.

Effect of Nitrogen on Water Content, Sap Flow, and Tolerance of Rice Plants to Brown Planthopper, Nilaparvata lugens

Water content (WC) and sap flow from leaf sheath of rice plants with varying nitrogen levels at different growth stages, and fluctuations in relative water content (RWC) of rice plants being damaged by brown planthoppcr (BPH), Nilaparvata lugens were determined in the laboratory, and the tolerance of rice plants to BPH at different nitrogen regimes was evaluated in the greenhouse at International Rice Research Institute (IRRI), the Philippines. The results indicated that both WC and RWC were increased significantly, as the amount of sap flow from rice plants was reduced statistically, with the increase of nitrogen content in rice plants. RWC in rice plants applied with high nitrogen fertilizer decreased drastically by the injury of BPH nymphs, while the reduced survival duration of rice plants with the increase of nitrogen content was recorded. These may be considered to be one of the important factors in increasing the susceptibility to BPH damage on rice plants applied with nitrogen fertilizer.

Potassium-Induced Regulation of Cellular Antioxidant Defense and Improvement of Physiological Processes in Wheat under Water Deficit Condition

Drought is the most common form of abiotic stress that reduces plant growth and productivity.It causes plant injuries through elevated production of reactive oxygen species(ROS).Potassium(K)is a vital plant nutrient that notably ameliorates the detrimental effect of drought stress in the plant.A pot experiment was conducted at the Laboratory of Plant Stress Responses,Faculty of Agriculture,Kagawa University,Japan,under controlled environment of green house to explore the role of K in mitigating drought severity in wheat(Triticum asevitum L.)seedlings.Three days after germination,seedlings were exposed to three water regimes viz.,100,50,and 20%field capacity(FC)for 21 days.Potassium was adjusted in Hoagland nutrient solution at 0,6 and 12 mM concentration and applied to pot instead of normal water.Results show that,water deficit stress notably reduced plant growth,biomass accumulation,leaf relative water content(RWC)along with reduced photosynthetic pigments.Increased amount of biochemical stress markers viz.,malondialdehyde(MDA),hydrogen peroxide(H_(2)O_(2)),methylglyoxal(MG),proline(Pro)as well as an impaired antioxidant defense system were observed in drought affected wheat plants.On the contrary,K supplementation resulted in improvement of biochemical and physiological parameters that worked behind in improving growth and development of the wheat plants.In addition,enzymes of ascorbateglutathione(AsA-GSH)cycle were also enhanced by supplemented K that accelerated the ROS detoxification process in plant.Although glyoxalse system did not performed well till MG was detoxified might following another short stepped pathways.Our results revealed that drought stressed plants showed better performances in terms of biochemical and physiological attributes,antioxidant defense and glyoxalase system,as well as ROS detoxification due to K supplementation with better performance at 12 mM K added in 50%FC growing condition.

Biomass and water partitioning in two age-related Caragana korshinskii plantations in desert steppe,northern China

Understanding of biomass and water allocation in plant populations will provide useful information on their growth pattern and resource allocation dynamics. By direct measurement, the biomass and water content partitioning were compared at the aboveground, belowground and whole-plant levels for artificial Caragana korshinskii populations between 6- and 25-year-old sites in desert steppe, northern China. The biomass was mainly allocated to third-srade branches at the aboveground level, and to firstand second-grade roots at the belowground level, and to aboveground parts at the whole-plant vegetative level. Those plant parts mentioned above became the major component of biomass pool of these shrub populations. Biomass pattern changed significantly at aboveground and/or whole-plant levels （P 〈0.05）, but not at belowground level （P 〉0.05） at 25-year-old site in comparison to 6-year-old site. Also, the water relations between dif- ferent plant parts changed considerably at all three levels from 6- to 25-year-old sites. These results imply that biomass pattern and relative water content of plant parts are correlated with the process of plantation development. The ratio of belowground to aboveground, though below 1, increased from 6- to 25-year-old site. These results suggest that these shrub populations can adjust biomass partition and relative water content of different compartments to alter their ecological adaptive strategies during stand development in desertified regions.

Selection of Rice Genotypes for Salinity Tolerance Through Morpho-Biochemical Assessment

The present study reported the morpho-biochemical evaluation of 15 selected rice genotypes for salt tolerance at the seedling stage. Growth parameters including shoot length, root length, plant biomass, plant turgid weight, plant dry weight along with relative water content were measured after exposure to saline solution （with electrical conductivity value of 12 dS/m）. Genotypes, showing significant differential responses towards salinity in the fields, were assessed through 14 salinity-linked morpho-biochemical attributes, measured at 14 d after exposure of seedling in saline nutrient solution. Relative water content, chlorophyll a/b, peroxidase activity and plant biomass were identified as potential indicators of salt tolerance. Principal component analysis and successive Hierarchical clustering using Euclidean distance revealed that Talmugur, Gheus, Ghunsi, Langalmura, Sabitapalui, and Sholerpona were promising genotypes for further breeding programmes in rice. The maximum Euclidean distance was plotted between Thavallakanan and Talmugur （7.49）, followed by Thavallakanan and Langalmura （6.82）, indicating these combinations may be exploited as parental lines in hybridization programmes to develop salinity tolerant variety.

Interactive Effects of Silicon and Potassium Nitrate in Improving Salt Tolerance of Wheat

Adequate regulation of mineral nutrients might be effective to ameliorate the deleterious effects of salts and help to sustain crop productivity, particularly in glycophytes, under salt stress. In this study, laboratory and greenhouse experiments were carried out at Agricultural and Natural Resources Research Centre in East Azerbaijan, Iran, to investigate the interactive effects of silicon and potassium nitrate in alleviating NaCl induced injuries in wheat（Triticum aestivum L.）. In the laboratory experiment, three winter wheat cultivars Pishgam, Afagh and Alvand were grown on sterile filter paper moistened with 20, 40, 60, 80, and 100 mmol L-1 NaCl solution. Results revealed that wheat cultivars were significantly different in their growth response to different concentrations of NaCl and Pishgam was found to be the most tolerant to NaCl stress, and used in the second part of study. In the greenhouse experiment, Pishgam was grown in a hydroponic system subjected to different NaCl levels（20, 60 and 100 mmol L-1） and treated by silicon（0, 2 and 4 mmol L-1, final concentration in nutrient solution using K2SiO3） and potassium nitrate（0, 0.5, 1, and 2 mmol L-1, foliar application）. The experimental design was factorial based on a completely randomized design with three replications. It was found that NaCl stress significantly increased proline accumulation and sodium content in the plant tissues while decreased potassium uptake and accumulation by plants. Moreover, plant weight, 100-seed weight, relative water content, chlorophyll content, and photosynthesis were also significantly affected by varying levels of NaCl. However, exogenous application of silicon and potassium nitrate reduced sodium uptake, increased potassium and consequently improved plant weight, 100-seed weight, seed yield, ear length, and photosynthesis rate. This study suggested that utilization of the salt-tolerant cultivar（Pishgam） combined with proper foliar application of potassium nitrate（2 mmol L-1） and silicon（4 mmol L-1） at the wheat booting stage might be a promising approach to obtain higher grain yield on saline lands.

Stress Ameliorative Effects of Indole Acetic Acid on Hordeum vulgare L. Seedlings Subjected to Zinc Toxicity

The heavy metals present in the environment accumulate in the plants and affect their productivity and yield.By entering the food chain,metals cause several serious health problems in human beings as well as in other organisms.Indole acetic acid(IAA)is known to act as a signaling molecule between symbiotic association of metal accumulating plants and plant growth promoting rhizobacteria(PGPR).Present study demonstrated a protective role of IAA against surplus Zinc(Zn)-induced toxicity to Hordeum vulgare seedlings.Elevated Zn concentrations suppressed the plant growth,caused a reduction in leaf relative water contents(RWC)and elevated free proline and non-protein thiols(NPT)accumulation.Zinc treatment also led to enhanced lipid peroxidation(MDA contents)as well as the activity of ascorbate peroxidase(APX),showing the involvement of antioxidative defense mechanism to reduce Zn induced toxicity.IAA oxidase activity was also observed to increase due to Zn treatment.IAA pretreatment of H.vulgare caryopsis could partly revert the Zn-induced toxicity in seedlings.

Detection of Quantitative Trait Loci for Yield and Drought Tolerance Traits in Soybean Using a Recombinant Inbred Line Population

To investigate the genetic basis of drought tolerance in soybean （Glycine max L. Merr.） a recombinant inbred population with 184 F2：7：11 lines developed from a cross between Kefengl （drought tolerant） and Nannong1138-2 （drought sensitive） were tested under water-stressed and well-watered conditions in field and greenhouse trials. Traits measured included leaf wilting coefficient, excised leaf water loss and relative water content as indicators of plant water status and seed yield. A total of 40 quantitative trait loci （QTLs） were identified： 17 for leaf water status traits under drought stress and 23 for seed yield under well-watered and drought-stressed conditions in both field and greenhouse trials. Two seed yield QTLs were detected under both well-watered and drought-stressed conditions in the field on molecular linkage group H and Dlb, while two seed yield QTLs on molecular linkage group C2 were found under greenhouse conditions. Several QTLs for traits associated with plant water status were identified in both field and greenhouse trials, including two leaf wilting coefficient QTLs on molecular linkage group A2 and one excised leaf water loss QTL on molecular linkage group H. Phenotypic correlations of traits suggested several QTLs had pleiotropic or location-linked associations. These results will help to elucidate the genetic basis of drought tolerance in soybean, and could be incorporated into a marker-assisted selection breeding program to develop high-yielding soybean cultivars with improved tolerance to drought stress.

Photosynthetic pigments and photosynthetic products of endophyteinfected and endophyte-free Lolium perenne L.under drought stress conditions

Endophyte-infected(EI)seeds of Lolium perenne L.were used to attain endophyte-free(EF)population by heating the seeds at 43℃for 15 min and then 57℃for 25 min.Relative water content(RWC),chlorophyll,soluble sugar and starch content of EI and EF populations under normal and drought stress conditions were compared to investigate the effect of endophyte infection on the host plant.Under severe stress,RWC of EI leaf was significantly higher than that of EF leaf,i.e.EI plants took more advantages over EF plants in water-holding ability.Under mild stress,endophyte could enhance soluble sugars in host plants to improve their osmotic ability.With stress intensification,the improvement of endophyte no longer existed,and more photosynthetic products(such as starch)accumulated in EI plants to survive through the undesirable conditions.In the next spring,EI populations will recover more rapidly than EF populations.The biomass of a population is closely related to its photosynthesis.Under severe stress,EI population significantly accumulated more biomass than EF population.As far as photosynthetic pigments were concerned,contents of Chla,Chlb and Car of EI plants were close to those of EF plants,which suggested that endophyte infection didn’t alleviate photosynthetic pigments from being destroyed by drought stress,and endophyte might improve photosynthesis ability of its host plant in other ways.