Effects Of Low Temperature And Low Light Stress On Physiological Characteristics Of Melon Seedlings

In the protected cultivation of melon, low temperature and low light was one of the main factors limiting the growth and development, yield and quality. Clarifying the mechanisms of melon seedlings under the low temperature and low light, breeding of cultivars tolerating to low temperature and low light were the most effective ways to increase the yield and quality of melon under the protected cultivation. However, few studies were concerned on the physiological responses and indexes selection of melon seedlings under low temperature and low light. To clarify the effects of low temperature and low light on the physiological characteristics and screening the indexes, the changes of morphological indexes, physiological and biochemical indexes and gas exchange parameters with melon cultivars "Yu Jin Xiang" and "Yi Li Sha Bai" under low temperature or/and low light were analyzed, thus providing theoretical and technical support for the screening and breeding of melon seedlings under low temperature and low light.In the low temperature experiment, we used the melon seedlings of three leaves to study the effects on seedling growth and physiological characteristics of low day-night temperature (10℃/5℃, day/night), low night temperature (18℃/5℃, day/night) for7days and recover growth in the normal temperature (25℃/18℃, day/night) for7days. The results showed that the low temperature mainly cause the damages of the shoot, significantly induced plant height, stem diameter, root length, stem fresh and dry weight, leaf fresh and dry weight, root dry weight, leaf number and leaf area, and significantly affected the content of MDA and soluble protein, activity of POD and CAT in the roots, activity of SOD and POD in the leaves; both of the two low temperature treatments significantly induced the seedling growth, but the growth recovery rate of the low night temperature treatment was faster than those of the low day-night temperature treatment;"Yu Jin Xiang" was more sensitive to the low temperature than "Yi Li Sha Bai".In the low light experiment, after10days of low light (20μmol·m-2·s-1,12h) treatment on the melon seedlings with three leaves, the indexes of seedling growth, physiological characteristics and gas exchange parameters were investigated. Results showed that the low light mainly cause the damages of the root, significantly induced root length, leaf dry weight, stem dry weight and leaf area, and significantly increased the content of MDA and activity of POD in the leaves.In the low temperature and low light experiment, after10days of low temperature and low light (10℃/5℃, day/night,20μmol·m-2·s-1,12h) treatment on the melon seedlings with three leaves, the indexes of seedling growth, physiological characteristics and gas exchange parameters were investigated. Results showed the whole seedling was damaged by the low temperature and low light, which significantly induced plant height, root length, stem fresh and dry weight, leaf fresh and dry weight, root fresh and dry weight, leaf number and leaf area, and significantly affected the content of MDA in the roots, content of soluble sugar and protein, activity of CAT in the leaves;"Yu Jin Xiang" was more sensitive to the low temperature and low light than "Yi Li Sha Bai".By analyzing the Venn diagram, there were synergy effect in the low temperature and low light treatment, which significantly affected the root dry weight, content of soluble sugar and protein and activity of CAT in the leaves; while the deleterious effects were mainly due to the low temperature; the root length stem dry weight, leaf dry weigh and leaf area could be used as the identification indexes of low temperature and low light tolerance.