PHOTOSYNTHESIS, PHOTORESPIRATION AND PROLINE ACCUMULATION IN WATER-STRESSED PEA LEAVES

Excised leaves of Pisum sativum L. were subjected to water stress for 24 h in the light and in darkness. Proline accumulation increased both in the light and in darkness as the relative water content decreased, but its increase was higher in the light. (CO2)-C-14 fixation in wate r-stressed leaves was severely inhibited. The activities of phosphoeno lpyruvate carboxylase and glycollate oxidase increased and those of ri bulose-1,5-bisphosphate carboxylase and phosphoglycollate phosphatase were not influenced by water stress. Photochemical reactions and elect ron transport in isolated chloroplasts were not significantly affected by low water potential in the leaves. Exogenously supplied glycollic and glyoxylic acids enhanced proline accumulation only in the light an d had no effect in darkness. The current photosynthesis during water s tress was probably not a major contributor of carbon to proline synthe sis. An alternative possibility is that photorespiration might be invo lved in this event.