Water Relations and Cell Wall Elasticity Quantities in<i>Phaseolus vulgaris</i>Leaves

Abstract

The investigations were designed to test osmotic adjustment, cell wall bulk elastic modulus and stomatal behaviour during and after water stress and rewatering in the primary and first trifoliolate leaf of Phaseolus vulgaris. Leaf water relations quantities fully recovered after rewatering within a few hours; diffusion resistance to vapour flow, however, required 6 h. Leaf growth recovery was considerably delayed. Osmotic adjustment was absent during water stress in both the primary and the first trifoliolate leaf. The bulk elastic modulus (εv), however, was lower for the primary leaf (higher elasticity) than for the trifoliolate leaves. These two types of leaves differed in their drought resistance in that the primary leaf exhibited wilting at the end of the stress period (7 d) while the trifoliolate leaf remained relatively turgid. The bulk elastic modulus of the cell wall changed almost proportionally with the turgor pressure (ψp). The structure coefficient (α), an indicator for the intensity of change of the bulk elastic modulus with turgor was 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 similar regression lines for the relation of (r) versus RWC1. The data suggest that greater drought resistance of the first trifoliolate leaf is related to a decreased bulk elastic modulus, but not to osmotic adjustment nor to differences in stomatal resistance during water stress.