Improving Photosynthetic Performance of Bread Wheat under Field Drought Stress by Foliar Applied Glycine Beta ine

Abstract

Nineteen bread wheat genotypes were selected to exa mine the effect of glycine betaine (GB, 100 mM) on various photosynthetic gas exchange parameters under drought stress and to study the relationship of these parameters w ith non-enzymatic antioxidants. Drought stress caused a significant decline in net CO 2 assimilation rate (P n ), stomatal conductance (g s ), intercellular CO 2 concentration (C i ) and transpiration rate (E) among the studied wheat genotypes, with the tolerant geno types characterized by higher net photosynthetic rate, lower drought susceptibility i ndex (DSI), and higher maintenance of glutathione content (GSH) and ascorbic acid (AsA) l evels than the sensitive ones. GB application significantly improved the photosynthet ic characteristics, particularly P n and g s , of studied wheat genotypes which could be due to more utilization of glutathione and increased levels of ascorbic acid in flag leaves un der drought stress. But this response was observed to be genotype specific. Positive correlat ion of AsA with DSI in GB treated plants, and of P n with GSH under drought stress and GB applied condi tions suggested the role of these non-enzymatic antioxidants in sustain ing photosynthetic efficiency and yield stability under prolonged field drought stress cond itions. Keywords: Non-enzymatic antioxidants, Photosynthetic efficie ncy.