Changes in water status and osmolyte contents in leaves and roots of olive plants (Olea europaea L.) subjected to water deficit

Two-year-old olive trees (Olea europaea L., cv. Coratina) were subjected to a 15-day period of water deficit, followed by 12 days of rewatering. Water deficit caused decreases in predawn leaf water potential (Ψ_w), relative water content and osmotic potential at full turgor (Ψ _π100) of leaves and roots, which were normally restored upon the subsequent rewatering. Extracts of leaves and roots of well-watered olive plants revealed that the most predominant sugars are mannitol and glucose, which account for more than 80% of non-structural carbohydrates and polyols. A marked increase in mannitol content occurred in tissues of water-stressed plants. During water deficit, the levels of glucose, sucrose and stachyose decreased in thin roots (with a diameter <1 mm), whereas medium roots (diameter of 1–5 mm) exhibited no differences. Inorganic cations largely contribute to Ψ _π100 and remained stable during the period of water deficit, except for the level of Ca²⁺, which increased of 25% in water-stressed plants. The amount of malate increased in both leaves and roots during the dry period, whereas citrate and oxalate decreased. Thin roots seem to be more sensitive to water deficit and its consequent effects, while medium roots present more reactivity and a higher osmotic adjustment. The results support the hypothesis that the observed decreases in Ψ_w and active osmotic adjustment in leaves and roots of water-stressed olive plants may be physiological responses to tolerate water deficit.