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Drought stress triggered by changes in the external water potential is an environmental commonplace in the life of a higher plant. The compatible osmolytes, such as proline plays an important role and act as osmoprotectants during stress. Though several attempts have been made to establish a relationship between proline accumulation and drought tolerance, not much is known about the regulation of proline metabolism in pigeonpea grown under drought conditions. It is, therefore, of equal importance to study the regulation of this biochemical phenomenon in plants during drought stress. In the present research, we anaylzed the activities of proline and proline metabolizing enzymes in two previously screened tolerant and susceptible pigeonpea cultivar under Polyentylene glycol induced drought stress. The proline accumulation data revealed that the tolerant cultivar GRG-295 accumulated higher proline content at different time intervals of drought stress. The comparative analysis of proline metabolizing enzymes like ornithine aminotranferase, P-5-C reductase, P-5-C dehydrogenase and Proline dehyrogenase were also carried out and it was revleaed that the accumulation of these enzymes were relatively higher in GRG-295 as compare to TAT-9903during different time interval of drought stress. The free proline content was gradually increased upon increase in stress duration in both the cultivars and significant higher activity was observed in GRG-295 as compare to TAT-9903. The activity of Ornithine aminotransferase and P-5-C reductase was increased upon increasing the stress period (upto 6 hour) and thereafter declined in bothe the cultivars while decrease in activity of proline oxidase and P-5-C dehydrogeanse was observed in both the cultivars upon increase in stress duration. The higher activities of these enzymes suggest their adaptive role in drought tolerant in pigeonpea. The present study indicated that accumulation of proline may provide a biochemical adaptation for plants during drought stress.

Keywords: Pigeonpea, Proline, Proline oxidase, Ornitihine aminotransferase, P5C reductase