| Rice, as one of major crops, is cultivated extensively in the world. 80% people over the world live on it. But its yield increase is limited by diseases, especially, sheath blight and blast. These fungal diseases develop broadly and cause serious damage, making the rice production reduce by 10% yearly in general and in some cases by 40% in particular regions, even no harvest in certain catastrophic fields. The major approach of food supply-increase lies in minimizing the effect on yields. The two major methods for fungal disease control are utilization of fungicides and resistant variety. But fungicide brings hidden troubles to human survivals and persistent development. So breeding resistant varieties isthe best choice, for it is most economical, safe, and effective.It undrew the prelude of transgenic breeding that the company of Monsanto Company obtained the first transgenic tobacco plant which had resistance to tobacco virus by transgenic technique in 1986. Since then, over 10 R genes have been cloned and transferred into various plants.Chitinase is a kind of hydrolytic enzyme which takes chitin as its substrate .Studies show that chitin is the primary component of cell walls of phytopathogenic fungi. It was reported that chitinase genes have been transferred into plants such as tobacco, bean and tomato and some transgenic plants showed significantly enhanced resistance against disease. So it seems possible to transfer exogenous chitinase genes into rice and make them express chitinase constitutively and increase the content of chitinase. Thus rice resistance to diseases is improvedNow the introduction of the exogenous genes into rice is mostly accomplished by Agrobacterium-mediaiQd. technique, biolistic bombardment, PEG and floral organ-mediated technique (pollen -tube pathway). Tranferring by floral organ is one of the transformation methods brought forward by Chinese molecular biologist -Zhou Guang-yu. It is applied widely in China and it brings economical, social and ecological benefit. However, some foreign specialists and scholars doubted there might be exist tanto incidental factors in the process. Consequently, it is quite necessary to ulteriorly discuss and analyze the feasibility which exogenous genes are introduced into and integrated into accept DNA by floral organ-mediated transfer.In this study. Serratia marcescens chitinase chiA gene and tobacco chitinase chiB gene were first transferred into rice plants, transgenic plants checked on J] generation by molecular biology methods, their GUS activity examined, their resistance to diseases identified and rice materials which better resist rice sheath blight and rice blast obtained.The main results from this study are as follows:1. Two plasmids were constructed suitable for rice transformation. A new 14.6kb plant expression plasmid pBG1112 was produced by inserting a 2.8kb CaMV 35S promoter/SchiA coding region/Nos terminator fusion into the polycloning sites of a 11.8kb binary vector pCAMBIA1301 and another new 13.9kb plant expression plasmid pBG1121 was produced by inserting a 2.1kb CaMV 35S promoter/TchiB coding region/Nos terminator fusion into the polycloning sites of pCAMBIA 1301.This two plasmids were then examined by restrictive enzymes, PCR. sequence analysis and chitinase activity.2. A feasible floral organ-mediated rice transformation system was established at the first time. The system included:1) A set of acceptable varieties suitable for transformation by floral organ-mediated techinique were Xiangjing 2,IR72,Youfeng 162.Xiangwanxian lO.Nanjing 3015,Nanjing 152 and Jiahezaozhan.2) pCAMBIA1301, with hygr selective gene and gus report gene in its T-DNA region, was proved to be a high efficient vector for rice.3) The optimal transformation conditions are as follows: the best time for rice transformation was l-3h after rice pollination; each flower was treated with 10 ul plasmid DNA(concentration is 105-240 u g/ml); the transformation rate of rice flower bagged with white sheepskin sacks was...
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