Changes in the water relation parameters and in the osmotically active solu
tes accumulating during leaf ontogeny were studied in leaves of two-year-ol
d, well-watered grapevines (Vitis vinifera L., cv. Savatiano). Results indi
cate that the apoplastic water fraction increased during leaf ontogeny whil
e there were no significant differences in osmotic potential at full turgor
. The relative proportion of monosaccharides to sucrose was significantly h
igher in immature leaves than in mature ones. Total inorganic ion accumulat
ion was similar in leaves of all ages while there was a significant increas
e in total amino acid content with leaf age. Total soluble carbohydrates an
d inorganic ions seem to be the major components of osmotic potential irres
pective of leaf age. The contribution of soluble carbohydrates to osmotic p
otential was higher in immature leaves but decreased with leaf age while th
e contribution made by inorganic ions followed the opposite pattern.