Osmolyte Accumulation, Membrane Stability and ABA Profiles in Rice Genotypes Exposed to Heat and Drought Stress

The effect of combined heat and drought stress on proline, chlorophyll stability index, membrane thermal stability and abscisic acid (ABA) contents were investigated to screen and study the physiological basis of heat and drought tolerance in three rice genotypes (ADT 43, TKM 9 and N 22). The stresses were imposed at panicle initiation (PI) and anthesis stages of crop growth. The genotype N 22 was found to be the tolerant followed by TKM 9 while ADT 43 was observed to the susceptible genotype based on the above physiological and biochemical traits. Irrespective of genotypes, anthesis stage stress brought about accumulation of osmolyte and ABA contents with membrane stability changes compared to stress at PI stage. ADT 43 recorded low proline content of (201 μg g-1), CSI of (52.5%), MTS of (24.39%) and ABA content of (0.587 μg g-1).While, N 22 recorded higher proline content of (252.6 μg g-1), CSI of (89.8%), MTS of (33.08%) and ABA content of (0.685 μg g-1). Higher proline and ABA contents with improved membrane stability was clearly demonstrated in the tolerant genotype (N 22) compared to susceptible genotype (ADT 43). This conforms that these biochemical traits can be used to screen rice genotypes to combined stresses and understand the mechanism underlying stress tolerance.