Effects of NaCl on Proline Synthesis and Utilization in Excised Barley Leaves

Abstract

Proline accumulation in NaCl-treated excised barley (H. vulgare cv. Larker) leaves was studied. Leaves were treated by placing the cut end in NaCl solutions and allowing the salt to enter the leaf via the transpiration stream. Leaves treated this way maintained turgor while the Na content increased and the osmotic potential decreased. Proline began accumulating after 12 h and continued accumulating over the subsequent 12-h period at an average rate of 0.6 .mu.mol per h per g fresh weight. During the time proline was accumulating, [14C]glutamate was added to measure the effects of salt on proline synthesis from glutamate and [14C] proline was added in separate experiments to determine the effect of salt on proline utilization. Salt treatment dramatically increased proline synthesis from glutamate. Proline utilization by oxidation and for protein synthesis was decreased by 50 and 60%, respectively, by the salt treatment. These effects are similar to the effects of drought and abscisic acid in barley leaves. The results indicate that common mechanisms cause proline to accumulate under these different stresses.