| For vegetable growth,temperature is one of the absolutely necessary factors. Temperature also is the mostly factor which restricts plant distributing in physical geography. Low temperature is harmful to vegetables growth. It is very cold in winter in west-China, furthermore, chilling often occurs there. Low temperature can threaten vegetables planting in greenhouse. Muskmelon planting is a developing style in greenhouse for these years, which represents an important effect on innovating agricultural structure and improving rural economy in west-China. Hence, it is indispensable to frame technique project of melon planting that researching how the chilling influence growth of muskmelon and how muskmelon respond to chilling in order to acclimatize itself to it. Two muskmelon cultivars, Huanghemi and Elizabeth were selected as material in this study to research the effect of low temperature on seedlings growth and on physiological & biochemical properties in seedlings leaves. The results were summarized as following: 1. Low temperature can inhibit height, the area of total leaves, fresh weight of the part above & under the ground, R/T, root vigor and dry weight accumulation of Muskmelon seedlings, the inhibitions of 15 ℃/5 ℃are serious than those under the other temperatures. Though height, the area of total leaves, fresh weight of the part above & under the ground of Elizabeth seedlings are lower than Huanghemi seedlings, the R/T ratio, root activity and dry weight accumulation of Elizabeth are higher than Huanghemi. It suggested that Elizabeth has stronger endurance to low temperature than Huanghemi. 2. The membrane permeability and MDA increased in both culivars with the decrease of temperature on the 1st and 3rd day. Then The activity of SOD, POD and CAT in huanghemi increased while time prolonged in some extent, however, out of the extent, all protected enzyme activities decreased while time prolonged. Under any temperature, the membrane permeability and MDA content of Elizabeth were less than Huanghemi, the protected enzyme activities of Elizabeth were more steadier-going than Huanghemi. It suggested that the membrane permeability, MDA and activity of SOD, CAT, POD can be used as target for identifying cold-tolerance cultivars. 3. The root activities of both cultivars increased at first and then decreased under any temperature. Being treated after 3 days, the contents of proline and soluble sugar under 15℃/5 ℃were much more than those under 25 ℃/15 ℃, but there was not obviously change when the time prolonged. However, the content of soluble protein decreased with the time prolonged. Because there were some differences of those index mentioned above between Huanghemi and Elizabeth, all the indexes can be used as indexes to show how the seedling can endure the cold. 4. Under low-temperature(15℃/5 ℃) the net photosynthetic rate (Pn) ,evaporation rate (Evap.), stomatal conductance (Gs),and chlorophyll fluorescence kinetics parameters such as Fm, Fv, Fv/Fm , Fv/Fo,FPSⅡof leaves decreased, while the thermal energy dissipation rate and photosynthetic limitation increased. The intercellular CO2 concentration(Ci) was higher than it under the other two temperature. The cause of reduction of Pn in muskmelon seedling leaves under low-temperature might be mainly non-stomata limitation. The results also suggested that chloroplast were injured by 15 ℃/5 ℃in long-term treatment. Elizabeth has more stonger photosynthesis than Huanghemi under low-temperature. 5. Elizabeth has stronger ability to endure low temperature, which can be selected as one of the cultivars for muskmelon planting in greenhouse. In conclusion, low temperature would damage muskmelon seedlings. For anti-season planting in greenhouse, it is very important that establishing technique project of melon planting based on selecting chilling-tolerance cultivar. It is also very important that improving temperature to avoid chilling-damage occurrence on muskmelon seedlings.
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