Preconditioning Alters Antioxidative Enzyme Responses in Rice Seedlings to Water Stress

Rice seedlings (Oryza sativa L.) were grown in a controlled environment and divided into control seedlings (CK1: 80% field capacity was always held), preconditioned seedlings (PT, 6 days mild drought for preconditioning–3 days re-watering–intermediate drought stress) and non-preconditioned seedlings (CK2, 9 days 80% field capacity and immediately followed by intermediate drought). Antioxidative enzyme (i.e., peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT)) activities, as well as malondialdehyde (MDA) content were measured in CK1 and PT after preconditioning and re-watering as well as CK1, PT and CK2 after intermediate drought. Mild drought preconditioning increased POD activity and MDA content, but no effects were observed on SOD and CAT activities. After re-watering, POD activity and MDA content of PT were similar to CK1. Intermediate drought stress significantly decreased SOD activity but increased POD and CAT activities, as well as MDA content in CK2. Compared to CK2, POD and SOD activities significantly increased, and no effect was observed on MDA content in PT. CK2 suffered more serious injuries than PT as indicated by higher MDA content, suggesting that mild drought preconditioning made rice seedlings modulate their defense response such that they could acclimatize more successfully to intermediate drought stress environment.