Effect of High Temperature on the Photosynthetic Characteristics and Antioxidant Enzyme Activities of Cucumber and Tomato in Greenhouse

The cucumber 'Jinyou 35' and the tomato 'Jinfen No.2' were used as materials,the environmental control test was conducted in artificial climate chamber,Nanjing university of information science and technology from January to June,2011.The effects of high temperature 32-40℃ with different time on leaf photosynthetic characteristics and antioxidant enzyme activity of cucumber,tomato were systematically studied,the results showed that the heat stress treatment significantly inhibited the photosynthetic rate of cucumber and tomato,with the processing time longer,photosynthetic rate decreased faster,when 38℃ or 40℃ sustained some hours,the maximum photosynthetic rate of cucumber and tomato was negative;with the levels of heat stress increasing and stress time lengthening,the PSII potential photochemical efficiency(Fv/Fm)of cucumber,tomato,photochemical quenching(qP) showed a downward trend,plants treated by 40℃,after recovering 5 days,Fv/Fm and qP values of cucumber and tomato were still in decline;when the temperature reached above 38℃,the SOD,POD,CAT,MDA of tomato and cucumber was in contrast to the case of the temperature under 38℃.According to the effects of high temperature on photosynthetic parameters of cucumber and tomato leaf,dividing heat stress into four grades: mild stress,moderate stress,severe stress,extremely severe stress,and ascertaining meteorological index.