Study On Effects Of High Temperature On PS Ⅱ And Its Defensive Mechanisms In Tomato

Tomato (Lycopersicon esculentum mill.) originating in the western highland South America is an important economic crop, and also a world-wide distribution, more consumption and major vegetables. Tomato is thermophilic, but can't withstand high temperature. High temperature in summer severely limits tomato production in southern provinces of China, and abnormally high temperature conditions often appeare in the protected (greenhouse and plastic greenhouse) cultivation. High temperature retards growth and development of tomato seriously or even death. The difference and defensive mechanisms were investigated in heat-tolerant (Zhongza No.9) and heat-sensitive (Chuanzhuyingtao) cultivars of tomato exposed to high temperature with measurement of the chlorophyll fluorescence parameters, antioxidant system and oxygen evolving activity. The results showed as follows:1. Fv/Fm,φPSⅡ, qP, NPQ, RC/CS and TRo/CS in heat-tolerant cultivar were higher than that in heat-sensitive cultivar under high temperature (25~50℃) stress. Activities of antioxidant anzymes including SOD, CAT, APX, POD and contents of antioxidant AsA in thermo-resistant cultivar were greater than that in heat-sensitive cultivar, and under high temperature condition, the contents of chlorophyll a, chlorophyll b, total chlorophyll andβ-carotenoid in heat-tolerant cultivar decreased less than in heat-sensitive cultivar..