CHANGES IN THE PHYTOHORMONE LEVELS DURING DROUGHT STRESS IN SOYBEAN (GLYCINE MAX .L) MERRIL

Abstract

The present study was calTied out to study the effect of inoculation with Rhizobium strain, drought and re-watering on the endogenous phytohormone levels and root nodulation of two cultivars of soybean (Glycine max L.) i.e.NARC 2000 (CVl) and NARC 2001 CV2. The seeds of cv 1 and cv2 were inoculated with carrier based inoculum of Rhizobium leguminosarum, strain TAL 377. Treatments made for both the cultivars include inoculated and un-inoculated stressed and their respective controls. Plants were grown under natural growing conditions. After 10 days of sowing, drought stress was imposed for 5 days by with-holding water supply. The stressed treatments were re-watered after 5 days and the plants were h,arvested after 48 hours of rewatering, Measurements for phytohormones were made at 10 days after sowing, 15 days after sowing and 19 days after sowing. The results have shown a marked effect of inoculation, drought and re-watering on the different parameters studied, As a result of drought all the stressed treatments have shown a decrease in the relative water contents and the Indole-3-acetic acid (IAA) and Gibberellic acid (GA) levels of the leaves, whereas the abscisic acid (ABA) contents increased. Inoculation has resulted in increased nodulation whereas; drought has shown decrease in the number of nodules. Drought has also reduced the volume of pink bacteroid tissue of the nodules. The results also showed that after 48h of re-watering, the relative water contents, the indole acetic acid (IAA) and Gibberellic acid (GA) contents of the leaves increased while the abscisic acid (ABA) contents decreased. The GNIAA ratio increased in the stressed treatments. The ABNlAA and ABAIGA ratio also increased in the stressed treatments but decreased after rewatering. The level ofrecovery was more in CVl as compared to CV2, The inoculated plants were more drought tolerant and showed early recovery following rewatering.