The role of organic solute and ion accumulation in osmotic adjustment in drought-stressed grapevines

Water relations, gas exchange as well as organic solute and ion accumulation were studied in the leaves of 2-year-old grapevines (Vitis vinifera L, cv. Savatiano) grown under well watered (control) and water stress conditions. Both osmotic potential at full turgor (Pi(100)) and at turgor loss point (Pi(0)) decreased significantly in stressed plants compared with the control. Photosynthetic rate, and stomatal conductance were also significantly lower in stressed plants. Starch concentration decreased almost threefold in stressed plants, while there were no significant differences in sugar accumulation between the two treatments. Total inorganic ion concentration increased rapidly in stressed plants and seems to be the major component of osmotic adjustment in stressed grapevines. Thus, the energetic cost of osmotic adjustment in grapevines using inorganic ions would be expected to be much lower than for those species using organic solutes. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.