Modulation of growth, photosynthetic capacity and water relations in salt stressed wheat plants by exogenously applied 24-epibrassinolide

Brassinosteroids promote the growth of plants and are effective in alleviating adverse effects of abiotic stresses such as salinity and drought. Under saline conditions, improvement in grain yield is more important than simple growth. Previously it was found that although foliar application of brassinosteroids improved growth of wheat plants, it did not increase grain yield. In present study, influence of root applied 24-epibrassinolide was assessed in improving growth and yield of two wheat cultivars. Plants of a salt tolerant (S-24) and a moderately salt sensitive (MH-97) were grown at 0 or 120 mM NaCl in continuously aerated Hoagland's nutrient solution. Different concentrations of 24-epibrassinolide (0, 0.052, 0.104, 0.156 mu M) were also maintained in the solution culture. Exogenous application of 24-epibrassinolide counteracted the salt stress-induced growth and grain yield inhibition of both wheat cultivars. Of the varying 24-epibrassinolide concentrations used, the most effective concentrations for promoting growth were 0.104 and 0.052 mu M under normal and saline conditions, respectively. However, root applied 0.052 mu M 24-epibrassinolide enhanced the total grain yield and 100 grain weight of salt stressed plants of both cultivars and suggested that total grain yield was mainly increased by increase in grain size which might have been due to 24-epibrassinolide induced increase in translocation of more photoassimilates towards grain. Growth improvement in both cultivars due to root applied 24-epibrassinolide was found to be associated with improved photosynthetic capacity. Changes in photosynthetic rate due to 24-epibrassinolide application were found to be associated with non-stomatal limitations, other than photochemical efficiency of PSII and photosynthetic pigments. Leaf turgor potential found not to be involved in growth promotion.