Foliar Application of Glycine Betaine Alters Sugar Metabolism of Wheat Leaves Under Prolonged Field Drought Stress

The present investigation was carried out to examine the alterations in contents of various sugars in a set of 19 wheat genotypes under drought stress. In addition, foliar application of glycine betaine (GB, 100 mM) was done to explore participation of this osmolyte in drought response mechanism. Drought stress caused a significant increase in total soluble sugars (TSS) and starch levels, at both maximum tillering and anthesis stages. Activities of sucrose phosphate synthase (Suc-P-syn) and sucrose synthase (Suc syn) were also increased in drought stressed plants at both the stages. Exogenous application of GB resulted in higher TSS under drought stress; however reduced levels of starch were observed at anthesis in GB treated plants. GB application caused a decline in activity of Suc-P-syn and Suc syn at both stages. The alterations in sugar levels of GB sprayed plants suggested that regulation of sugar metabolism could undergo modifications (upstream or downstream) in presence of osmolytes like GB. Genotype-specific response to GB spray resulted in yield benefits in selected genotypes under drought stress.