| Tomato (Lycopersicon esculentum Mill.), ranking the top in the production area and total yield among all the vegetable crops in the world, plays a great role in vegetable production in China. Tomato belongs to thermophilic vegetable crops, whose most optimum temperature range is 20~25℃ and adaptive temperature range is 15~33℃. However, in many Chinese areas, daytime temperature often goes beyond the favorable temperature range for tomato's florescence and fruit set, even going up to 35 ℃ or more, in the summer open field, sunlight-greenhouse and plastic greenhouse during the crossing period bewteen summer and spring, which leads to damage tomato growth and to restrict its development. Especially, in the last ten years, due to the gradually increasing greenhouse effect, the temperature rises. Therefore, the high temperature becomes one of the main limitary factors to stunt the noraml development of tomato. It is necessary to study the physiological characteristics and the adjusting capability of tomato's genotypic difference in the term of heat tolerance. Such research will provide help for the breeding of heat-tolerant tomato variety and to improve the heat-tolerant cultivation technology.Based on a large account of collection of domestic and oversea tomatoes and their mutants, our work evaluated the heat tolerances of nine different genotypic tomatoes, and selected the '030701015' and'Zhongshu No. 6' that own the distinct difference in the term of heat tolerance. The effect of foliar treatment with brassinolide (BR) on the their response to high temperature also were discussed. Besides, two plant expression vectors expressing phytoene synthase gene (crtB) were constructed to establish a great base for the future study on the effect of PSY gene over-expression on fruit set in the condition of high temperature. The main results are as follow:(1) The obvious differences among physiological and biochemical reaction characteristics and their change degrees of various genotypic tomatoes were found. The increased degrees of antioxidant enzymes (APX, CAT, G-POD and SOD) activities and free proline of '03070105' were higher than those of the other varieties. Therefore, "03070105" was identified as a high heat-tolerant tomato variety;'LA3120', 'LA4133', 'LA3320' and 'LA3847' did not show distinct heat tolerance capacity on the physiological indexes, and the heat tolerance degree of 'LA3120' and 'LA3847' were elementarily considered as higher than that of 'LA4133' and "LA3320";The heat tolerance of "e1042b" was little higher than that of 'e2124b' and the mutants' parent 'M82', but the further investigation in field will be necessary.(2) Heat-tolerant tomato '03070105' and heat-sensitive tomato 'Zhongshu No. 6' were selected to be foliar treated with BR. A large difference between heat-tolerant variety and heat-sensitive variety of treated young tomato seedling was found. The chlorophyll and carotenoid content of the heat-tolerant variety increased markedly;the changes of its antioxidant enzymes (APX, CAT, G-POD and SOD) activities, Spm and Spd content were not obvious compared with the control. The chlorophyll and carotenoid content of the sensitive-tolerant variety was not obviously different from the control;its antioxidant enzymes (APX, CAT, G-POD and SOD) activities and Spm content were obviously higher than those of the control, but the Spd showed no obvious change.(3) Positive cloned plasmid pCRTB was double digested by Sac I and BamU restriction enzymes. The production of restriction digestion, respectively backward with the CaMV 35S and E8 promotor, was ligated into plasmid pCAMBIA 1301. The constitutive-expression vector, named 'pCA 35S-crtB', containing CaMV35S promoter expressing crtB gene and the seed-specific expression vector, named 'pCA E8-crtB', containing E8 promoter following crtB gene were constructed for the future work to regulate caroteniod biosynthesis in fruits by genetic engineering. |
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