Water stress-induced osmotic adjustment in expanding leaves of tepary bean (Phaseolus actifolius Gray) seedlings

Abstract

Tepary (Phaseolus actifolius Gray) beans perform better than common beans (Phaseolus vulgaris) under drought conditions. The mechanism of drought tolerance in tepary bean seedlings was explored by determining the water potential (WP), osmotic potential (OP), relative water content (RWC), free sugar concentration, and the level of K ion within the expanding leaves. Two week old tepary bean seedlings were subjected to a gradual water stress with sorbitol solutions exhibiting OP values of -0.19 MPa and -0.47 MPa. Turgor remained constant whereas WP, OP and RWC declined following the stress treatment. Osmotic adjustment (OA) occurred in each treatment but the contribution of sucrose and fructose was minor. Some sorbitol was translocated to leaves and contributed to OA. The decrease of K ions in leaves indicated that these ions did not contribute to the OA. A significant decrease in cell size was observed as determined by decrease in TW/DW ratio.