Electrolyte and Pi Leakages and Soluble Sugar Content as Physiological Tests for Screening Resistance to Water Stress in<i>Phaseolus</i>and<i>Vigna</i>Species

Abstract

With the aim of selecting physiological tests for the screening of drought tolerant species, we have studied the behaviour of bean leaf discs treated with PEG 600 (−1.13 MPa) for 4 h. The kinetics of electrolyte and Pi leakages and of soluble sugar and starch content were studied during 24 h rehydration of the leaf discs. These four tests were related, respectively, to cell and chloroplast membrane integrity and to photosynthetic or sugar mobilization ability. The results obtained showed that stress caused by PEG induced an increase in the leakage of electrolyte of 4 to 7 times and of Pi up to 10 and 28 times, and a decrease in soluble sugar and starch content. These phenomena were stimulated by darkness. The magnitude of the physiological responses varied according to the species but correlated well with each other. Therefore, the tests used are indicators of cell and membrane integrity and they allowed us to propose a classification of the species according to their cell sensitivity to water deficit. The sequence obtained was: Phaseolus vulgaris, sensitive, Phaseolus acutifolius and Vigna radiata moderately tolérant and Vigna unguiculata, tolerant. This classification agrees well with that of drought resistance of these species when grown in the field.