OVEREXPRESSION OF DELTA-PYRROLINE-5-CARBOXYLATE SYNTHETASE INCREASES PROLINE PRODUCTION AND CONFERS OSMOTOLERANCE IN TRANSGENIC PLANTS

Proline (Pro) accumulation has been correlated with tolerance to droug ht and salinity stresses in plants. Therefore, overproduction of Pro i n plants may lead to increased tolerance against these abiotic stresse s. To test this possibility, we overexpressed in tobacco the mothbean Delta(1)-pyrroline-5-carboxylate synthetase, a bifunctional enzyme abl e to catalyze the conversion of glutamate to Delta(1)-pyrroline-5-carb oxylate, which is then reduced to Pro. The transgenic plants produced a high level of the enzyme and synthesized 10- to 18-fold more Pro tha n control plants. These results suggest that activity of the first enz yme of the pathway is the rate-limiting factor in Pro synthesis. Exoge nous supply of nitrogen further enhanced Pro production. The osmotic p otentials of leaf sap from transgenic plants were less decreased under water-stress conditions compared to those of control plants. Overprod uction of Pro also enhanced root biomass and flower development in tra nsgenic plants under drought-stress conditions. These data demonstrate d that Pro acts as an osmoprotectant and that overproduction of Pro re sults in the increased tolerance to osmotic stress in plants.