This study has investigated mechanisms conferring beneficial effects of exogenous application of 24-epibrassinolides (EBL) on plant growth and performance under saline conditions. Barley seedlings treated with 0.25 mg l-1 EBL showed significant improvements in root hair length, shoot length, shoot fresh weight and relative water content when grown in the presence of 150 mM NaCl in the growth medium. In addition, EBL treatment significantly decreased the Na+ content in both shoots (by approximately 50%) and roots. Electrophysiological experiments revealed that pre-treatment with EBL for 1 and 24 h suppressed or completely prevented the NaCl-induced K+ leak in the elongation zone of barley roots, but did not affect root sensitivity to oxidative stress. Further experiments using Arabidopsis loss-of-function gork1-1 (lacking functional depolarization-activated outward-rectifying K+ channels in the root epidermal cells) and akt1 (lacking inward-rectifying K+ uptake channel) mutants showed that NaCl-induced K+ loss in the elongation zone of roots was reduced by EBL pre-treatment 50- to 100-fold in wild-type Col-0 and akt1, but only 10-fold in the gork1-1 mutant. At the same time, EBL treatment shifted vanadate-sensitive H+ flux towards net efflux. Taken together, these data indicate that exogenous application of EBL effectively improves plant salinity tolerance by prevention of K+ loss via regulating depolarization-activated K+ channels.

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Effect of different concentrations of indole acetic acid (IAA) under varying soil water deficit conditions on two barley cultivars viz. B-99094 and Jau-87 was investigated in soil filled earthen pots. There were six treatments including control each with four replicates. Three concentrations of IAA (0, 15 and 30 mg l -1 ) were applied as foliar spray 30 days after germination. After hormone application, half of the pots were subjected to one cycle of water stress (withholding of water till incipient wilting), followed by regular watering. Plant height, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency relative water content, dry biomass, and grain yield/plant were significantly reduced by water stress. However, IAA treatments alleviated the adverse effect of water stress and successful in enhancing the plant growth and yield of barley cultivars. Barley cultivar Jau-87 performed better than B-99094. IAA application was effective in enhancing growth and photosynthetic efficiency of barley both under normal and water stress conditions.