Leaf age effects on solute accumulation in water-stressed grapevines

The effects of leaf age on water relations, organic solute. and total ion a ccumulation were studied in mature and immature leaves of two-year-old grap evines (Vitis vinifera L., cv. Savatiano) grown under water stress conditio ns. Osmotic potential at full turgor decreased significantly in leaves of s tressed plants, irrespective of leaf age, indicating the occurrence of an a ctive osmotic adjustment. The apoplastic water fraction (A) increased durin g leaf ontogeny in both control and stressed plants. However, the values of A were lower in stressed plants. Starch concentration decreased significan tly in both mature and immature leaves during the drought cycle, while the relative proportion of monosaccharides and sucrose was markedly different i n immature leaves compared to mature. The accumulation of total inorganic i ons, induced by drought, was also age dependent, increasing significantly w ith leaf age, while there were no significant differences in total amino ac ids content. Inorganic ions and carbohydrates seem to be the major componen t of osmotic adjustment in mature and immature grapevine leaves, respective ly.