| Leaf lettuce (Lactuca Sativa L.) is also called lettuce, which belongs to the leaf types of the genus Lettuce in the composite family. Lettuce is currently domestic a very important characteristics of vegetable species, large consumption, market demand wide. Lettuce likes the cold and has no high temperature resistance that the suitable growth temperature of lettuce is 15-25?, when the temperature is over 30 ?, the growth is hindered and quality decline. Therefore, the high temperature hindered the production of lettuce in summer. Arbuscular mycorrhizal (arbusculr mycorrhiza, AM) fungi can form symbiotic mycorrhiza root and established system with plant root. Research shows that AM fungi can enhance the function of plant resistance high temperature, high salt, drought, heavy metal toxicity and soil borne diseases. At present, there is little research on the heat resistance of AM fungi in leaf lettuce. Author carried out comparative cultivation experiment under high temperature of artificial simulation, screening of resistant varieties of lettuce. The heat resistant varieties inoculated with different AM fungi, the dominant species, with AM fungi can enhance plant resistance effect, explore the impact of high temperature on the heat resistance of AM fungi lettuce. Preliminary study on the mechanism of AM fungi to improve the heat resistance of lettuce and provide theoretical basis for the application of AM fungi in improving heat tolerance of lettuce. The main results are as follows:1. Under pot conditions, we selected 42 leaf lettuce cultivars from home and abroad, and carried out comparative cultivation experiment under high temperature of artificial simulation, then determined and analyzed the heat injury index, root system activity, leaf relative conductivity and content of oxygen free radicals in leaf blades. Based on the above screened indexes, we chose'Kasitenaiyou'lettuce,'Kuxiye'lettuce,'Xibanya' lettuce, 'Shuangzi'lettuce and'Meiguo'lettuce as leaf lettuce cultivars with relatively higher tolerance to high temperature.2. We used Funneliformis mosseae, Glomus intraradices, Glomus versiforme three inoculated 'Shuangzi' lettuce, the study found that AM fungi enhanced root activity and chlorophyll content of lettuce, promoted the growth of lettuce, and decreased the content of nitrate. Among them, F. mosseae improved the lettuce fresh weight 19% and dry weight of 21%, root activity increased 40%, leaf nitrate content decreased by 12%. Lettuce had the highest mycorrhizal dependence on F. mosseae and F. mosseae was the best species to promote the growth of lettuce.3. Under greenhouse conditions, high temperature (35?) AM fungi F. mosseae, G intraradices, G versiforme improved the lettuce defense enzyme activity and root activity, reduced malondialdehyde (MDA) content and membrane permeability, increased the osmotic adjustment substance content in high temperature (35?). It was concluded that inoculation with AM fungi could improve lettuce heat tolerance, of which F. mosseae was superior and should be a possible effective strains of increasing heat tolerance of lettuce in the production.4. Under greenhouse conditions, by using CIRAS-3 photosynthesis determination system to measure photosynthesis index, HT7700 Hitachi transmission electron microscope observation of chloroplast ultra microstructure, continuous excitation fluorometer M-PEA and JIP-test data analysis method to analyze the characteristics of chlorophyll fluorescence characteristics. It was found that the AM fungi could maintain the integrity of the electron transfer chain in the PS II reaction center of lettuce leaves and enhance the ability of electron transport chain receptors on the receptor side; At the same time, the high temperature stress of chloroplast was alleviated, which reduced the damage of photosynthetic membrane, enhanced the photosynthetic capacity of lettuce under high temperature stress, and enhanced the heat tolerance of lettuce.5. Using fluorescence quantitative PCR technology to analyze the AM fungi induced by high temperature stress on the LsHsp90 gene up-regulated expression, which is one of the reasons for the heat resistance of AM fungi. |
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