Water Relations and Cell Wall Elasticity Quantities in Phaseolus vulgaris Leaves

The investigations were designed to test osmotic adjustment,cell wall bulk elastic modulus and stomatal behaviour duringand after water stress and rewatering in the primary and firsttrifoliolate leaf of Phaseolus vulgaris. Leaf water relationsquantities fully recovered after rewatering within a few hours;diffusion resistance to vapour flow, however, required 6 h.Leaf growth recovery was considerably delayed. Osmotic adjustmentwas absent during water stress in both the primary and the firsttrifoliolate leaf. The bulk elastic modulus (_v), however, waslower for the primary leaf (higher elasticity) than for thetrifoliolate leaves. These two types of leaves differed in theirdrought resistance in that the primary leaf exhibited wiltingat the end of the stress period (7 d) while the trifoliolateleaf remained relatively turgid. The bulk elastic modulus ofthe cell wall changed almost proportionally with the turgorpressure (_p). The structure coefficient (), an indicator forthe intensity of change of the bulk elastic modulus with turgorwas higher for the primary than for the first trifoliolate leaf.The leaf diffusion resistance (r), below the turgor loss point,changed proportionally with the solute potential with very similarregression lines for the relation of (r) versus RWC ¹. The datasuggest that greater drought resistance of the first trifoliolateleaf is related to a decreased bulk elastic modulus, but notto osmotic adjustment nor to differences in stomatal resistanceduring water stress. Key words: Phaseolus vulguris, Water stress, Recovery, Cell wall elasticity