Comparative expression of two abscisic acid-inducible genes and proteins in seeds of aromatic indica rice cultivar with that of non-aromatic indica rice cultivars.

As an integral part of stress signal transduction, the phytohormone abscisic acid (ABA) regulates important cellular reactions, including up-regulation of stress-associated genes, the products of which are involved directly or indirectly in plant protection. Being accompanied by an increased endogenous ABA level, the matured seeds, embryo and aleurone tissues of cereals accumulate several genes and proteins, associated with desiccation. The present study was aimed at investigating how the contrasting rice genotypes, varying in their salt-stress sensitivity, differ with respect to the expression pattern of two abiotic stress-inducible genes, Rab16A and SamDC, and corresponding proteins, in the seeds, at the background level (dry or water-imbibed state) and ABA-imbibed conditions, which could be related to the varietal differences in tolerance. The rice genotypes selected were M-1-48 (salt-sensitive), Nonabokra (salt-tolerant) and Gobindobhog (aromatic). An extremely low abundance of Rab16A or practically undetectable SamDC transcripts were observed in M-1-48 and Gobindobhog seeds under control conditions, induced only after exogenous ABA treatment, whereas they were expressed at a much higher level even in dry and water-imbibed seeds of Nonabokra, and lesser induced by ABA. The RAB16A (=dehydrin) and SAMDC protein expression in the three varieties were also identical to the gene expression patterns. Thus, the expression was stress-inducible in M-1-48 and Gobindobhog, while constitutive in Nonabokra. Our study reflected the similarity of the molecular responses to exogenous ABA of the seeds of the aromatic rice Gobindobhog to that of the salt-sensitive M-1-48, in exhibiting lower expression of stress-tolerant proteins only after stress. This work also proved that variation in gene/protein expression in seeds could be highly correlated with the variation in the tolerance mechanism of rice varieties.