Glutamine synthetase expression and pyrroline-5-carboxylate reductase activity influence proline accumulation in two cultivars of foxtail millet ( Setaria italica L.) with differential salt sensitivity

Abstract

Two cultivars of foxtail millet ( Setaria italica L.) seedlings with different salt sensitivity were exposed to different regimes of NaCl stress in order to establish the importance of the salt induced glutamine synthetase (GS), its altered expression pattern and pyrroline-5-carboxylate reductase (P5C reductase) activities on proline accumulation. Salt stress resulted a significant accumulation of proline in two cultivars of foxtail millet seedlings. However, the accumulation was found to be more in tolerant cultivar, Prasad than susceptible cultivar, Lepakshi and positively correlated with the increased GS and P5C reductase activities. GS an important enzyme plays a pivotal role in re-assimilation of NH 4 + in higher plants. It is evident from immunoblot analysis that the glutamine synthetase expression was found to be increased at 150 and 200 mM NaCl stress in both cultivars indicates the availability of sizable pool of glutamate, a precursor for proline biosynthesis. P5C reductase a key enzyme in proline biosynthesis showed increased activity with salt treatments and positively correlated with the proline accumulation and the stress tolerance of two cultivars. Further, the GS and P5C reductase activities and the degree of proline accumulation were relatively lesser in salt susceptible cultivar than salt tolerant cultivar. In conclusion, proline accumulation was due, at least in part to increase in the salt induced GS activity coupled with the increased P5C reductase activity.