ADAPTATION OF LEAVES OF VITIS-VINIFERA L TO SEASONAL DROUGHT AS AFFECTED BY LEAF AGE

The aim of this study was to evaluate the water, turgor, osmotic poten tials and leaf water content during leaf ontogeny using both the press ure volume and the psychrometric techniques. The symplasmic water frac tion of the total water content decreased with leaf age from 78 % in i mmature leaves to 62 % in old leaves. The capability for osmoregulatio n was almost the same in immature and mature leaves but decreased in o ld leaves. The volumetric modulus of elasticity (epsilon) was lower in immature leaves (12.7 MPa) and increased in mature (22.5 MPa) and old leaves (28 MPa). The high elasticity of young leaves seems to be an i mportant strategy for adaptation to drought.