Physiological responses and membrane integrity in three Vigna genotypes with contrasting drought tolerance

In the present work some dehydration-induced responses at whole plant and cellular levels were evaluated in three Vigna genotypes (V. glabrescens, Vg; V. unguiculata cv. EPACE-1; V. unguiculata cv. 1183) from different origins. Changes in leaf stomatal conductance (gs), membrane lipids composition and abscisic acid (ABA) content were determined under water stress. Membrane integrity was assessed through leaf discs dehydration with polyethylene glycol (PEG 8000, -1.3 MPa), and expressed as an injury index (I%).. In EPACE-1 and 1183, rapid stomatal closure at early stages of dehydration was related with the ability to accumulate endogenous ABA. On the contrary in Vg stomata closed at lower leaf relative water content as ABA increase was delayed. In 1183, high I% values occurred in PEG-dehydrated discs, and lipid degradation was observed even under moderate water stress (S1), becoming significant under more severe drought (S2). Also, along drought imposition this genotype presented a continuous leaf ABA increase that probably contributed to early visual tissue senescence. Vg and EPACE-1 presented lower I% values, probably denoting the ability to preserve membrane integrity. In EPACE-1 this was achieved through a quite stable lipid content, while in Vg new membrane lipids were synthesized. It is suggested that a higher protoplasmic tolerance in EPACE-1 and Vg might be related to stable and low endogenous ABA contents under increasing water deficit.