Foliar Application of Abscisic Acid Improves Drought Tolerance of Sugarcane Plant under Severe Water Stress

An experiment was set up to investigate the interrelationship between drought induced abscisic acid (ABA) biosynthesis and antioxidative defense system, and to confer the role of foliar application of ABA in imparting drought tolerance to the sugarcane plant. A drought tolerant variety ROC22 was treated with T1 (drought-water withholding), T2 (drought + foliar application of 15 ?M ABA) and C (control, normal irrigation). Drought treatment (T1) enhanced the ABA concentration in leaves but it was significantly higher in combined treatment (T2), suggesting its biosynthesis was triggered in leaves by the ABA application. Both T1 and T2 resulted in an increase in proline, H2O2 and MDA content but the plants applied with ABA were found to resist the increase in MDA content. Overproduction of H2O2 in plants treated with T1 was followed by higher activities of CAT, GPX, GR and APX enzymes. A decrease in H2O2 level with increasing stress in T2 treated plant showed effectiveness of ABA induced highly expressed antioxidative defense system which was found to be vanished progressively, in the plants treated with the drought only. The results clearly suggests that though the tolerant variety showed an enhanced protective system against drought conditions, the foliar application of ABA further improved its tolerance by continuously triggering the over expression of antioxidative defense syste