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 solutes accumulating during leaf ontogeny were studied in leaves of two-year-old, well-watered grapevines ( Vitis vinifera L., cv. Savatiano). Results indicate that the apoplastic water fraction increased during leaf ontogeny while there were no significant differences in osmotic potential at full turgor. The relative proportion of monosaccharides to sucrose was significantly higher in immature leaves than in mature ones. Total inorganic ion accumulation was similar in leaves of all ages while there was a significant increase in total amino acid content with leaf age. Total soluble carbohydrates and inorganic ions seem to be the major components of osmotic potential irrespective of leaf age. The contribution of soluble carbohydrates to osmotic potential was higher in immature leaves but decreased with leaf age while the contribution made by inorganic ions followed the opposite pattern.