SALINITY TOLERANCE OF RICE (ORYZA-SATIVA L) WITH REFERENCE TO ENDOGENOUS AND EXOGENOUS ABSCISIC-ACID

Experiments conducted in a phytotron on three rice varieties of differ ent salinity tolerance revealed an increase in the content of endogeno us abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi sal t-tolerant), but in Pokkali (salt-tolerant) and IR28 (salt-sensitive) the increase in ABA content was marginal. Under salinity stress, in ge neral, 5 weekly sprayings of ABA (10(-4) mol L(-1)) decreased Na and K concentrations in the shoot to the extent of 29.5% and 3.3%, respecti vely. However, ABA application significantly improved the K/Na ratio a s well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and s hoot dry weight. The results are discussed in relation to possible mec hanism of salinity tolerance.