Exogenous Spermidine Alleviates the Oxidative Damage in Cucumber Seedlings Subjected to High Temperatures

Abstract

Heat tolerance is considered to be an essential feature for cucumber (Cucumis sativus) production, and it has been suggested that higher antioxidant ability could prevent the oxidative damage in plants caused by high-temperature stress. We aimed to investigate whether the application of exogenous spermidine (Spd) increases antioxidant activities and, therefore, elevates the heat tolerance of cucumber. Cucumber seedlings (cv. Jinchun No. 4) showing moderate heat tolerance were grown in climate chambers to investigate the effects of exogenous Spd (1 mm) foliar spray treatment on the activities and isozyme levels of antioxidative enzymes under both high-temperature stress 42/32 °C (day/night) and normal temperature 28/18 °C (day/night). On high-temperature stress, the activities of superoxide dismutase and ascorbate peroxidase were significantly reduced; the catalase activity was initially lower and then increased, whereas the peroxidase activity was initially higher and then decreased. The levels of these isozymes also changed differently. On treatment with exogenous Spd, the activities of these antioxidant enzymes were noticeably enhanced, and the isozyme zymogram expression had some changes. It was concluded that foliar spray with Spd effectively improved the total antioxidant ability of cucumber seedlings and, therefore, enhanced the tolerance of the plants to high-temperature stress.