Comparative physiological and molecular responses of a common aromatic indica rice cultivar to high salinity with non-aromatic indica rice cultivars

In an attempt to understand the molecular basis of salt-stress response in the aromatic rice Gobindobhog, a comprehensive analysis encompassing physiological or biochemical assays and gene expression studies under high salt (200 mM NaCl) supply regimes were initiated and compared with a salt-sensitive (M-1-48) and salt-tolerant (Nonabokra) rice. The detrimental effects of salinity stress were the most pronounced in Gobindobhog, as reflected by the maximally increased root to shoot ratio, the highest chlorophyll degeneration, the highest foliar concentration of Na+ ions and peroxide content, with their maximum increment after salt treatment. The amplification of oxidative damages was further stimulated by the accumulation of putrescine and lipid peroxidation-derived toxic degradation products (increased malondialdehyde and lipoxygenase activity), which were comparable in M-1-48 and Gobindobhog. Antioxidants like anthocyanin and particularly cysteine and the osmolytes like reducing sugar, proline and polyamines (spermidine and spermine) showed the highest level in Nonabokra. While the inhibition of catalase activity occurred in all the varieties following salt-stress, the maximum induction in guaiacol peroxidase activity, elevated cysteine and proline levels in Gobindobhog probably constituted the detoxification mechanism obligatory for its survival. Intensification of the aroma content with salt treatment was markedly noted in Gobindobhog. A very low abundance of Rab16A/SamDC transcript and the corresponding proteins were observed both in M-1-48 and Gobindobhog, induced only after salt-stress, whereas they were constitutively expressed in Nonabokra. Thus, our data reflect Gobindobhog as a salt-sensitive cultivar, susceptible to high-stress-induced growth-inhibition, ion imbalances, membrane/oxidative damages with lower expression of stress-tolerant genes.