Novel Light-Dark Change of Proline Levels in Halophyte (Mesembryanthemum crystallinum L.) and Glycophytes (Hordeum vulgare L. and Triticum aestivum L.) Leaves and Roots under Salt Stress

Abstract

Proline accumulation was determined in a facultative halophyte, Mesembryanthemum crystallinum and glycophytes, barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) Proline accumulation preceded the shift of CAM in M. crystallinum and did not occur in the continuous darkness. The novel light-dark change of proline level (high in the light and low in the dark) was observed in leaves of all three plants. Proline levels of shoots in barley and wheat also showed the same light-dark change, suggesting that proline accumulated in the leaves in the light was not translocated to other tissues in the dark period. These results suggest that proline has a bifunctional role in the acclimation to high salt stress; an osmoregulant role in the light, and a substrate for dark respiration to supply energy to compartmentation of ions into vacuole in the dark.