Energy costs of salinity tolerance in crop plants: night-time transpiration and growth.

Plants grow and transpire during the night. The aim of the present work was to assess the relative flows of carbon, water and solutes, and the energy involved, in sustaining night-time transpiration and leaf expansive growth under control and salt-stress conditions. Published and unpublished data were used, for barley plants grown in presence of 0.5-1 mM NaCl (control) and 100 mM NaCl. Night-time leaf growth presents a more efficient use of taken-up water compared with day-time growth. This efficiency increases several-fold with salt stress. Night-time transpiration cannot be supported entirely through osmotically driven uptake of water through roots under salt stress. Using a simple three- (root medium/cytosol/vacuole) compartment approach, the energy required to support cell expansion during the night is in the lower percentage region (0.03-5.5%) of the energy available through respiration, under both, control and salt-stress conditions. Use of organic (e.g. hexose equivalents) rather than inorganic (e.g. Na+ , Cl- , K+ ) solutes for generation of osmotic pressure in growing cells, increases the energy demand by orders of magnitude, yet requires only a small portion of carbon assimilated during the day. Night-time transpiration and leaf expansive growth should be considered as a potential acclimation mechanism to salinity.

Methods for the Simple and Reliable Assessment of Barley Sensitivity to Abiotic Stresses During Early Development.

Physiological assays that facilitate screening for various types of responses to abiotic stresses are well established for model plants such as Arabidopsis; however, there is a need to optimize similar tests for cereal crops, including barley. We have developed a set of stress assays to characterize the response of different barley lines during two stages of development-seed germination and seedling growth. The assays presented, including the response to osmotic, salt, oxidative stresses, and exogenously applied abscisic acid, can be used for forward screening of populations after mutagenesis as well as for phenotyping of already isolated mutants, cultivars, or breeding lines. As well as protocols for stress treatments, we also provide methods for plant stress response evaluation, such as chlorophyll a fluorescence (ChlF) and image analysis.

An improvement of the diffusion model for assessment of drought stress in plant tissues.

The article discusses an improvement of a previously developed method for assessment of ion leakage from plant tissues as a gauge of membrane and cell wall performance under stressful environment. It employs conductometric measurements of the ion efflux from leaves and their quantitative interpretation by a theoretical model based on the laws of diffusion. Experimental data are readily fit with the model and results are in accordance with relative water content of dehydrated barley (Hordeum vulgare) seedlings of two distinct cultivars. Some new parameters obtained from fitting are proposed as reliable indicators of the leaf status. They appear to be helpful in further distinguishing the behavior of two separate cellular structures with respect to their electrolyte permeability. It is concluded that the established method based on the kinetics of ion leakage is adequate for evaluation of contrasting genotypes under normal and stress conditions. Furthermore, it could be used as a simple and powerful tool for routine analysis and screening for drought tolerance in crops.

Bias correction for estimated QTL effects using the penalized maximum likelihood method.

A penalized maximum likelihood method has been proposed as an important approach to the detection of epistatic quantitative trait loci (QTL). However, this approach is not optimal in two special situations: (1) closely linked QTL with effects in opposite directions and (2) small-effect QTL, because the method produces downwardly biased estimates of QTL effects. The present study aims to correct the bias by using correction coefficients and shifting from the use of a uniform prior on the variance parameter of a QTL effect to that of a scaled inverse chi-square prior. The results of Monte Carlo simulation experiments show that the improved method increases the power from 25 to 88% in the detection of two closely linked QTL of equal size in opposite directions and from 60 to 80% in the identification of QTL with small effects (0.5% of the total phenotypic variance). We used the improved method to detect QTL responsible for the barley kernel weight trait using 145 doubled haploid lines developed in the North American Barley Genome Mapping Project. Application of the proposed method to other shrinkage estimation of QTL effects is discussed.

A transient assay system for the assessment of cell-autonomous gene function in dehydration-stressed barley.

Drought is a serious, worldwide problem for crop production and also affects yields of barley and wheat, together with other stressors such as frost, viral diseases, or fungal pathogens. Although a number of candidate genes have been identified by transcriptome approaches in recent years, only very few have been tested in functional assays for a beneficial effect on drought tolerance. Here, a transient assay system in microprojectile-bombarded barley leaves is described that allows the functional testing of dehydration stress-related candidate genes by RNA interference (RNAi) or overexpression. Cellular stress or damage in dedydrated leaves is reported by a reduced accumulation of slowly maturing, native red-fluorescing protein DsRed that is known to be sensitive to denaturing conditions. After a dehydration-stress period of 4 d during which the relative fresh weight of leaves was kept at 60-66% of initial fresh weight, a reproducible reduction of normalized DsRed fluorescence was observed. In order to obtain proof of concept, a number of barley mRNAs homologous to drought response genes were selected and targeted by transient induced gene silencing (TIGS). TIGS of four tested genes resulted in a significantly stronger decrease of normalized DsRed fluorescence in dehydration-stressed leaves, whereas they had no effect in fully turgescent control leaves. These genes encode barley drought-responsive factor HvDRF1 (DREB2-like), dehydrin 6, late embryogenesis-abundant protein HVA1, and the vacuolar sodium/proton antiporter HvHNX1. The four targeted transcripts were also found to accumulate rapidly in dehydration-stressed barley leaf segments. The results suggest a value of the TIGS system for functional pre-screening of larger numbers of drought or dehydration stress-related candidate genes in barley.

Size characterization of barley starch granules by gravitational field-flow fractionation: a rapid, low-cost method to assess the brewing capability of different strains.

Cereal starch occurs as two types of micrometer-sized granules, large and small. Large starch granules are more susceptible to enzymatic hydrolysis. When cereal starch is used for fermentation processes, as in brewing of barley malt, the barley strains with the highest content of large starch granules should be preferred. Gravitational field-flow fractionation (GFFF) is a separation method able to fractionate starch samples at low cost and short analysis time. In this work, the search for the best GFFF conditions for the analytical separation of barley starch within an inter-laboratory approach is presented. For different barley strains cultivated under monitored conditions the size distributions of starch granules is here quickly monitored and characterized by GFFF. As a consequence, dimensional characterization of barley starch can allow for the selection of the most suitable strains with the lowest content of non-degradable starch.