Effect of gradual and shock chilling stress on abscisic acid,soluble sugars and antioxidant enzymes changes in 'Sultana' grapevine

Plants may show different behaviours during exposure to low temperature stress through various mechanisms. in this study,the chilling responses of 'sultana' grapevine were investigated during a gradual chilling (2 °c/h) and also during a shock chilling (5 °c/h) from 24 °c to 4 °c. after artificial chilling stress,electrolyte leakage,lipid peroxidation,hydrogen peroxide production and antioxidant enzymes activities were measured in all plants leaves. moreover,the potential of plant to accumulate abscisic acid and osmoregulants were compared under both gradual and shock chilling stresses. based on the results,a significant difference was found between the electrolyte leakage,lipid peroxidation and hydrogen peroxide content of plants under two chilling regimes. these indices were found to be higher in shock chilling stressed plants compared with gradual chilling stressed vines because of the lower catalase,peroxidase and ascorbate peroxidase activities. moreover,gradual chilling stressed vines exhibited higher accumulation of abscisic acid,proline and total phenolic compounds. the chlorophyll degradation and relative water content were lower in gradual cold stressed plants. glucose and fructose,unlike sucrose showed higher concentration in gradual cold stressed vines. totally,under gradual chilling stress grapevine plants showed better cold acclimation by lower oxidative stress and higher accumulation of osmoregulants in compared with shock chilling stressed vines.