| Eggplant is a kind of thermophile vegetable crop, often suffer cold and disease. It is also encountered chilling hurt in winter and spring controlled cultivation, and it can results in the delay the growth, decline of yield and quality. The optimum growth temperature for eggplant is 22～30℃, under 17℃the growth will be slowed down; and under 10℃the plant will follow metabolic disturbance. The critical temperature of chilling injury is 7.2℃. In protected cultivation of eggplant, the temperature injuries come mainly from chilling injury. Regular physical activity vegetables impeded due to chilling injury, and chilling injury happens in the average temperature of 0～10℃. The level of chilling damage to plants is depends not only on the temperature level, also on the duration of low temperature. As the eggplant production has strong regional habit, in the cold- resistance study of fruit vegetables, there are lots of research report on tomato and pepper, but few on eggplant.Eggplant's cold-resistance can be controlled by many specific cold-resistance genes, so cold-resistance of eggplant is influenced by many factors. A large number of scholars pointed out that single index can not reflect the real cold-resistance of plants right. Evaluating all kinds of factors comprehensively can obtain the correct conclusions and it will be the focus of future researches.Growth of eggplant is sensitive to its environment. Currently, the research of eggplant's cold-resistance physiology focus mainly on looking for the right rootstock and the suitable outside sources of chemicals, such as salicylic acid (SA), abscisic acid (ABA) and so on, to increase the eggplant's cold-resistance capability. With the development of new exogenous substances, the research of cold resistance of eggplant will bring new opportunities.5-aminolevulinic acid (ALA) is a key precursor of the porphyrin's biosynthesis and it exist in nature plants and animals widespread. ALA is needed for the biosynthesis of chlorophyll, protoheme, vitamin B, phytochrome and other substances. It connects Photosynthesis and Respiration widely. Researches abroad showed that on certain concentration of 5-aminolevulinic acid, it can improve the stress resistance capability of plants. Hotta, etc. left the rice plant in the 1mg/L ALA for 1 day, then shifted to 5℃for 5 days, the experimental results showed that after ALA treatment, the dry matter of the plant increased 72%, the survival improved 30% because of the old leaves' life extended. Watanabe, etc. had compared 12 plant growth regulators and after the experiment of the salt tolerance of cotton, found that with 1.5% NaCl treatment, all plants were dead, but with the 100mg/L～300mg/L ALA treatment, the death was only 20% to 30% and compared with the untreated with NaCl, the plant dry weight and fresh weight were not significant.Spermidine (Spd) is a kind of substance of polyamines. It is a biologically active substance existing in prokaryotes and eukaryotes widely. Also, it is a class of low molecular weight aliphatic nitrogen-containing base which generally exist in plants. Ai-Rong Liu, etc. showed that by using different concentrations of Spermine and Spermidine to treat the seed and the bud of rape. they all have the most suitable concentration in the range of 0.01～1mmol/L which can increase plants stress resistance capability.Xue Wang, etc. found that if used 0.1～0.5 mmol/L Spd, it can reduce the toxicity which produced by Hg2+, when the spray concentration of Spd reach to 1mmol/L, SOD, POD, CAT, APX activity have gradually started to decrease. Currently, the latest study found that soaking Spd could increase the antioxidant enzyme's activities of tomato seedlings, thereby reduced salt stress on tomato seedlings' growth inhibition, particularly for the salt-sensitive species is more significant. There were experiments showed that under salt stress, low concentrations of exogenous Spd soaking can promote the germination of tomato seeds and increase the activity of protective enzymes in leaves, and 0.25 mmol/L Spd did have the best effect.Salicylic acid is a secondary metabolites in plants. It is a widespread material and have been used widely. All plants can protect and restrain the damage that caused by drought stress through photosynthesis and antioxidant. Under the drought stress, the content of leaves' SA increased. The result showed that SA can enhance plant drought resistance. Others showed that SA can enhance the heat resistance of plants. After using 0.1-0.5mmol/L SA to soak tomato and soybean seed, the plants showed the capability of resisting high temperature, low temperature and drought stress, and irrigating roots through the salicylic acid had the similar result. Yan Sun, etc. found that 250mg/L SA can increase cucumber seedling index effectively and enhance the resistance of cucumber.In this study, through compared with the three exogenous substances that can improve the chilling resistance of eggplants, and comprehensive analysis the different cold-resistance indexes in eggplant, so that we can select a better exogenous substance and study its mechanism to provide the theoretical and technical basis for the new exogenous substance's further application, promotion and research in the breeding and cultivation of eggplant under the low temperature stress.The results as follows:1.By using the three exogenous substances of different concentrations (SA, ALA, Spd) and CK to deal with the eggplant seedling leaves in four-leaf-stage and keep them under 5℃for 4 days, then measured electrical conductivity and compared the influence on the cold-resistance capability of three kinds of exogenous substances. Experiments show that compare the 5-aminolevulinic acid (ALA) and spermidine (Spd) with the CK and salicylic acid (SA), ALA and Spd can reduce the conductivity significantly, improve the cold resistance of eggplant and reduce the injury to eggplant seedlings when face the low temperature stress. When apply 3mmol/L SA, the conductivity is minimum.2.By using four different concentrations of 5-aminolevulinic acid (ALA) (0.05mg/L,0.5mg/L, 1mg/L and 5mg/L) and CK and measured SOD, POD, CAT levels everyday, after 4 days to measure the content of proline (Pro), malondialdehyde (MDA) and chlorophyll (chl), experiments show that compared with other concentrations, the 5-aminolevulinic acid (ALA) of lmg/L can reduce the damage of low temperature on eggplant seedlings significantly and improve the cold resistance of eggplant.3.By using four different concentrations of spermidine (Spd) (0.01mmol/L, 0.1mmol/L,0.5mmol/L, 1mmol/L) and CK in four-leaf-stage eggplant seedling and keep under 5℃for 4 days and measured SOD, POD, CAT levels everyday, after 4 days to measure the content of proline (Pro), malondialdehyde (MDA) and chlorophyll (chl), experiments showed that compared with other concentrations, the spermidine (Spd) of 0.5mg/L can reduce the damage of low temperature on eggplant seedlings significantly and improve the cold resistance of eggplant.4.By using lmg/L 5-aminolevulinic acid (ALA),0.5mmol/L spermidine (Spd) and CK in four-leaf-stage eggplant seedling and keep under 5℃for 4 days, then measured the content of electrical conductivity, malondialdehyde (MDA), proline (Pro)and ascorbic acid. Experiments showed that the optimal concentration ALA is more effective than the optimal concentration of Spd in improving cold resistance of eggplant.
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