Drought Stress-Induced Alterations in Source–Sink Relationships in Barley During Grain Development

Drought is one of the major constraints affecting sucrose metabolism and limits crop production worldwide. In the present study, key enzymes of sucrose metabolism and their metabolites were determined in the flag leaf, peduncle, and grains of four barley genotypes, namely DWRB 101, 432 ICARDA, 430 ICARDA, and Jyoti, at different days after anthesis (DAA) under drought stress. Imposition of stress led to upregulation of sucrose phosphate synthase (SPS) and sucrose synthase (SS) activities in the peduncle of 432 ICARDA and 430 ICARDA, which was positively correlated with sucrose content. Alkaline invertase activity increased during early stages of grain development in the peduncle of all four genotypes. Upon exposure to drought stress, starch content declined in the grains of all barley genotypes except DWRB 101 at the 40th DAA. In peduncle, SPS was positively correlated to acid invertase (r = 0.491) at the 1% level of significance, which might be related to rapid circulation of sucrose in the resistant barley genotypes, namely DWRB 101 and 432 ICARDA. Further, DWRB 101 exhibited upregulation of SS at the 40th DAA, which suggested that SS might be providing sufficient substrates for starch synthesis. Hence, the scrutiny of data showed that DWRB 101 has better carbon partitioning and might perform better under drought conditions.