Polyethylene Gycol (PEG) Induced Water Stress in Four Different Genotypes of Pea Seedlings and Evaluation of The Induced Defense Mechanism

Abstract

The present work was undertaken on artificially induced water stress on pea seedlings under in vitro conditions in order to select the drought tolerant line. Artificial water stress was induced with PEG-6000 on 15-day old seedlings of four varieties for 4, 8 and 12 days. The activities of antioxidative enzymes like peroxidase, catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase were assayed in the stressed and control plants. POX activity was increased in the initial stages of stress, but its activity was decreased significantly on the 12th day in all the varieties. APOX also showed a similar trend but the maximum activity was noted in Var 3 on the 8th day. CAT activity decreased in var 1 and var 2 when compared with the control, which, however, increased significantly in var 3 and var 4. A slight increase in the GR activity was observed in var 1 and var 2 at the initial stages of the drought stress but its activity decreased significantly on the 12th day in both these varieties when compared with control plants. However, its activity also increased steadily in var 3 and var 4. Maximum SOD activities were noted on the 4th day of drought stress in all four varieties but its activities decreased steadily on the subsequent 8th and 12th days when compared with control. When antioxidative activities were compared among the four varieties, var 3 and var 4 showed maximum increase in antioxidant activity during the period of drought stress. Among the four varieties, var 3 and var 4 showed greater accumulation of H2O2 during the stress days and were maximum at 12th day. Lipid peroxidation also increased in the same varieties. Maximum proline content was noted in both the root and leaf of var 3, followed by var 4. It was further noted that the chlorophyll content decreased significantly in all four varieties in subsequent longer drought stresses. The accumulation of proline content was steadily higher with an increase in the stress length in all the four varieties. During the drought stress, all the varieties showed an increase in ascorbate content but, it was maximum in var 4 followed by var 3 and the least ascorbate was noted in var 1. The present findings indicate that water stress induces oxidative stress in all the four varieties. However, antioxidative mechanisms were found to be more pronounced in var 4 which, therefore, may be considered as the most tolerant to drought stress.