Antioxidant defense system in young olive plants against drought stress and mitigation of adverse effects through external application of alleviating products

Two years old Koroneiki olive trees were subjected to drought stress after foliar application of products with known ameliorating function, i.e. glycine betaine (GB), kaolin clay particles (KL) and 5-hydroxybenzimidazole (Ambiol). Measurements were taken after product application, within the stress period and after re-watering. Lipid peroxidation and electrolyte leakage, as well as antioxidant defence factors (enzymes such as catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (POD), glutathione reductase (GR) and phenolic compounds and ascorbic acid) were assayed. Drought induced a significant increase of lipid peroxidation and an elevation of the activity of SOD, POD and APX, while a drastic rise of oleuropein was also determined. KL application resulted in increased total phenol concentration as well as an increased activity of SOD, POD under drought. GB application increased the concentration of total flavanols during the drought period while right after application a sharp increase of oleuropein concentration was detected. Ambiol application decreased the total phenol concentration during the stress period, but enhanced POD and APX activity and total ascorbic acid concentration. During the relief period few significant differences were determined. All products alleviated to some degree the stress imposed by water deprivation, with Ambiol and KL being more efficient in preventing oxidative damage of olive trees. Based on the present results it could be assumed, that the combined use of alleviating products with different mode of action, could trigger multiple defence mechanisms, resulting in more efficient mitigation of abiotic stress.