Alterations in stem sugar content and metabolism in sorghum genoptypes subjected to drought stress

Changes in stem sugar content due to drought stress imposed at the early reproductive stage were studied in seven genotypes of sorghum differing in their ability to store stem sugar. Out of the seven genotypes, two genotypes (ICSSH 58 and SPV 1411) that showed little variation in total sugar levels at the 5th internode from the peduncle on exposure to drought treatment and five genotypes (ICSV 25275, ICSV 25280, PVK801, RSSV 9 and M 35-1) that showed significant increases in total sugar levels on drought exposure, were grouped and used for comparative studies on sugar metabolism. Drought stress led to a decrease in sucrose synthase activity in the catabolic direction in both groups. However, neutral and acid invertase activities increased significantly in the genotypes ICSSH 58 and SPV 1411, and correlated to the increase in reducing sugar content on exposure to drought. Hydrolysis of stem sugars probably had a role to play in osmotic adjustment on exposure to drought stress and correlated to retention of sap volume in these genotypes. However the activities of sugar metabolizing enzymes did not correlate to their gene expression levels. On resuming irrigation after twenty days of drought stress and studying the yield parameters at physiological maturity stage, it was observed that grain yields, stalk yields and juice volume were lower in the plants recovering from drought stress as compared to the irrigated controls. In some genotypes like ICSV25275, ICSSH58 and M35-1, there were similar losses in grain yields and stem sugars due to the brief drought exposure, indicating source limitation of photoassimilates. However, in other genotypes like ICSV25280, PVK801 and RSSV9, grain yield losses were less than stem sugar losses in drought exposed plants as compared to controls, suggesting mobilization of sugars from the storage internodes to the developing panicle, to ensure viable progeny. Hence accumulation of stem sugars appears to be an adaptive strategy in some, but not all sorghum genotypes, against drought stress

H Qazi et al., 'Alterations in stem sugar content and metabolism in sorghum genoptypes subjected to drought stress', Functional Plant Biology, pp.1-32, CSIRO Publishing, 2014