DROUGHT-INDUCED ACCUMULATION OF SUGARS AND PROLINE IN RADICLE AND PLUMULE OF TOLERANT WALNUT VARIETIES DURING GERMINATION PHASE

Drought stress is a major factor in reducing growth, development and production of walnuts. Stress was applied with polyethylene glycol (PEG) 6000 giving osmotic water potentials of: zero (control) and six drought stress levels of -0.10, -0.50, -0.75, -1.00, -1.50 and -2.00 MPa. Solutes accumulation of walnut (Juglans regia L.) varieties and selections (‘Z₃₀’, ‘Z₅₃’, ‘Z₆₇’, ‘Z₆₀’, ‘Z₆₃’, ‘K₇₂’, ‘B₂₁’, ‘V₃₀’, ‘Panegin₂₀’, ‘Hartley’, ‘Pedro’, ‘Vina’, ‘Lara’, ‘Serr’, ‘Rounde de Montignac’, ‘Chandler’) were determined after drought stress. A higher amount of soluble sugars and a lower amount of starch were found under stress. Soluble sugars concentration increased (from 29.62 to 227.63 mg/L DW) in roots and shoots of tolerant varieties when the studied varieties were subjected to drought stress, but starch content significantly (P≤0.05) decreased (by 16 to 84%) in all varieties. This suggests that sugars play an important role in Osmotic Adjustment (OA) in walnut in germination phases. The free proline level also increased (from 10.23 to 610.4 mg/ml FW) in response to drought stress and the increase in ‘Chandler’ was higher than other varieties. Proline may play a role in minimizing the damage caused by dehydration. Increases of proline content in shoots was higher than in roots, but increases of soluble sugar content and decreases of starch content in roots was higher than shoots.