Physiological responses of kiwifruit plants to exogenous ABA under drought conditions

We studied the physiological responses to abscisic acid (ABA) when 2-year-old potted plants of kiwifruit (Actinidia deliciosa) were grown under moisture stress. Leaves treated with 60 mu M exogenous ABA through various means had less severe damage when water was limiting, and sprayed plants showed relatively greater drought resistance. This indicates that ABA improves tolerance in kiwifruit, reducing membrane permeability and enhancing the activities of antioxidant enzymes, e.g., peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). Exposure to ABA led to higher levels of antioxidants, such as ABA and glutathione (GSH), while altering the amounts of endogenous hormones-ABA, indole-3-acetic acid (IAA), and Gibberellin (GA)-and organic oxalate, malate, and citrate in the leaves. Although daily applications of ABA were more effective than a single spray event, the effect of treatment, i.e., avoiding tissue damage and increasing plant resistance, was more apparent on Day 4 than on Day 6. No difference in response was apparent between control plants (regular irrigation) and those sprayed with ABA on Day 4 of the drought period.