Chilling is one of the major abiotic stresses limiting yield and quality of many important crops. For better understanding of chilling stress responses in tobacco (Nicotiana tabacum), growth rate and antioxidant enzymes of seedlings in 2 tobacco cultivars, viz., MSk326 (chilling sensitive variety) and Honghuadajinyuan (HHDJY, chilling tolerant variety) at chilling temperature (5oC) were studied. The results showed that the relative growth rate in chilling period to that in recovery period was significantly higher in roots than that in shoots for both cultivars, suggesting that shoots growth was more easily affected by chilling stress. Chilling stress increased peroxidase (POD) activity and reduced superoxide dismutase (SOD) activity in shoots of HHDJY, and catalase (CAT) activity was little affected. In the roots of HHDJY, chilling stress increased SOD and CAT activities, and had little effect on POD activity. For MSk326, chilling treatment increased SOD activity in shoots and declined CAT activity in roots. MDA concentration in both varieties was increased under the chilling stress, while it was decreased after seedlings were recovered growth for 4 d at normal temperature (25oC). It showed that tobacco seedlings might have the capacity of recovering from chilling injury for a short term. The relationship between the growth rate and antioxidant enzyme activity was analyzed by stepwise regression. It was found that there was a close relationship between relative growth rate of tobacco seedlings and CAT activity under chilling stress condition and regression equations containing CAT could be used in predicting seedling growth rate of tobacco under chilling stress condition.
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