Comparison of response of two C3 species to leaf water relation,proline synthesis,gas exchange and water use under periodic water stress

Water relations, proline content and gas exchange of leaf were investigated under periodic water stress for two C3 plants (eggplant and tomato) in a greenhouse to study comparative adaptive responses. Although both species showed reduced water content of leaf and increased osmolality and proline content under low soil water potential, the recovery capacity after the stress was better in eggplant than tomato. Both species over-accumulated proline under low soil water potential and returned to its initial concentration during the recovery, indicating that proline may act as an osmoprotectant during drought. Proline was directly corresponding with osmolality during stress, and dehydration stress reduced the gas exchange parameters such as transpiration rate (ET), stomatal conductance (GS), and photosynthesis rate (Pn). At the final stage of the experiment both species showed 2.6 and 3.3 times lower Pn and 27 and 19 times lower GS for eggplant and tomato, respectively, as compared to control. But after stress was relieved by rewatering, both plants increased GS for 2 to 3 times and Pn for 4.5 times. Eggplant showed better water use efficiency (WUE) in relation to fruit production under the stress than tomato. Higher biomass allocation at root and fruit parts in eggplant indicated more efficient recovery than that of tomato. These findings inferred that both C3 plants developed internal complementary drought survival mechanism by lowering relative water content, increasing proline, and decreasing stomatal conductance but eggplants withstood the periodic draughting better than tomato, mainly due to its ability to recover from a water stress condition.