The effect of long-term osmotic stress was investigated in leaves of two common bean lines, with contrasting tolerance: Flamingo (tolerant) and coco blanc (sensitive). Water relations, organic solute, ion accumulation and amino acids content as well as osmotic adjustment (OA) were studied during an extended exposure to osmotic stress. Osmotic stress was applied by means of 50 mM mannitol for 15 days. At the end of the stress period, both osmotic potential at full turgor (Ψ100) and at turgor loss point (Ψ0) decreased significantly in stressed plants compared with the control. The decrease being greater in the sensitive line, showed a greater OA compared with flamingo. Sugars contents increased in stressed plants and seem to be the major components of osmotic adjustment in stressed common bean leaves. The increase was more marked in coco blanc. Osmotic stress tolerance could thus not be associated with higher OA. The possible role of decreased leaf cell elasticity (εmax) is discussed in relation to osmotic stress tolerance in this species.
Key words: Common bean, carbohydrate accumulation, growth, osmotic stress, osmotic adjustment, P-V curve, water relations.
AWC, Apoplastic water content; DAS, days after seedlings emergence; DW, dry weight; LWP, leaf water potential; OA, osmotic adjustment;PAR, photosynthetic active radiation; P-V curve, pressure-volume curve; RWC,relative water content; SEM, scanning electron microscopy; ΔΨl, degree of osmotic adjustment; ε, tissue elastic modulus; εmax, cell elasticity; Ψ, osmotic potential; Ψ0, osmotic potential at turgor loss point; Ψ100, osmotic potential at full turgor.
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