MOLECULAR AND PHYSIOLOGICAL-RESPONSES TO ABSCISIC-ACID AND SALTS IN ROOTS OF SALT-SENSITIVE AND SALT-TOLERANT INDICA RICE VARIETIES

The Indica rice (Oryza sativa L.) varieties Pokkali and Nona Bokra are well-known salt tolerance donors in classical breeding. In an attempt to understand the molecular basis of their tolerance, physiological a nd gene expression studies were initiated. The effect of abscisic acid (ABA) on total proteins in roots from 12-d-old seedlings of Pokkali, Nona Bokra, and the salt-sensitive cultivar Taichung N1 were analyzed on two-dimensional gels. The abundance of ABA-induced proteins was hig hest in the most tolerant variety, Pokkali. Three ABA-responsive prote ins, present at different levels in roots from tolerant and sensitive varieties, were further characterized by partial amino acid analysis. A novel histidine-rich protein and two types of late embryogenesis abu ndant (LEA) proteins were identified. Protein immunoblotting revealed that the levels of dehydrins and group 3 LEA proteins were significant ly higher in roots from tolerant compared with sensitive varieties. En dogenous ABA levels showed a transient increase in roots exposed to os motic shock (150 mM NaCl). Peak ABA concentrations were 30-fold higher for Nona Bokra and 6-fold higher for Pokkali compared with Taichung N 1. Both the salt-induced endogenous ABA levels and a greater molecular response of root tissue to ABA were associated with the varietal diff erences in tolerance.