COMPARATIVE PHYSIOLOGY OF SALINITY AND DROUGHT STRESS TOLERANCE IN INDICA AND JAPONICA RICE SEEDLINGS

Abstract

Salinity and drought stress is the major and frequently co-occurring abiotic stresses which disturb the morphophysiological and biochemical attributes within the plants. Therefore, the present study was conducted to investigate the morphophysiological and biochemical responses of two popular cultivars of rice (BRRI dhan29 and BRRI dhan48 from indica and Koshihikari from japonica) under salinity and drought stress either alone or in combination at early vegetative stage. Eighteen-day-old seedlings were subjected to salinity (150 mM NaCl), drought (PEG-6000, 15%) and combined salinity and drought (150mM NaCl + PEG-6000, 15%) in vitro for 72h. Salinity and drought alone and in combination increased mortality rate, decreased seedlings height, reduced biomass, abated water status and lowered photosynthetic pigments content in all three cultivars but the worst effects were observed in BRRI dhan29 and Koshihikari compared to BRRI dhan48. Moreover, under stress conditions compared with control a substantial increase was seen in the rate of electrolyte leakage (EL), elevated levels of H 2 O , lipoxygenase (LOX) activity, malondialdehyde (MDA) and methylglyoxal (MG) content which indicated an enhancement of lipid peroxidation in rice cultivars. The reduction of reduced ascorbate (AsA), lower AsA/DHA and GSH/GSSG ratio under salinity stress and combined stress indicate the disruption of redox balance in the cell. But under stress conditions compared with other varieties BRRI dhan48 showed lower Na 2 + /K + ratio, elevated proline (Pro.) content, higher AsA and reduced glutathione (GSH) activity, higher AsA/DHA and GSH/GSSG ratio and enhanced activities of MDHAR, DHAR, GPX and glyoxalase system. The results suggested that higher tolerant capacity of BRRI dhan48 against salinity, drought and combined stress is related to lower Na iii

+ /K + ratio, enhanced Pro content and better performance of glyoxalase system and antioxidant defense for scavenging reactive oxygen species (ROS) and these results may provide insight into possible responses associated with single or combined stress of salinity and drought in rice cultivars.