Osmotic stress-induced alterations in rice (Oryza sativa L.) and recovery on stress release

In laboratory experiments, rice plants cv 'Kranti' were stressed osmotically using polyethylene glycol '6000' and mannitol, whereas, in pots, plants were drought stressed by withholding water supply. Both osmotic and drought stress influenced different aspects of nitrogen metabolism, resulting in a decline in the activities of aspartate aminotransferase, alanine amino-transferase and an increase in protease activity accompanied by increased free proline and alterations in other amino acid content. An influence on alpha-amylase activity, total free sugars and starch contents was also observed, reflecting the impact of water stress on interconversion between starch and simpler sugars. Effects of polyethylene glycol '6000' as an osmotic agent were more consistent than those of mannitol during short-term (18 h) stress imposition, probably because of slight absorption of mannitol. Since the recovery for most of the parameters was substantial on release of stress, one can infer that the duration and magnitude of stress applied in the present experiments did not cause major permanent alterations in the rice cultivar 'Kranti.' The significant basic information gathered in such experiments, particularly on recovery potential, can be utilised for varietal screening.