Changes in the solutes contributing to osmotic potential during leaf ontogeny in grapevine leaves

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.