Basic studies on production of disease resistant plants by molecular control of phosphate metabolism

2，5-寡腺苷合成酶(2，5-AS)在感染病毒的动物细胞中诱导产生25-寡腺氨酸[PPPA(2p5A)n]。导入2，5-AS基因的烟草不仅对病毒(黄瓜花叶病毒和烟草花叶病毒)表现出抗性，而且对由立枯丝核菌引起的立枯病和由白粉病引起的白粉病等真菌病害也表现出抗性。磷酸盐(K-PO4)处理能更好地提高抗病性。磷酸盐处理的寄主植物的细胞壁比未处理的厚。因此，推测磷酸盐处理的抗性增强是通过抑制真菌的入侵而引起的。在含有2，5-AS基因的转基因植株中，核糖核酸酶(RNase)活性的提高幅度大于非转基因植株。磷酸盐处理对酶活性的提高更明显，似乎也起到了抑制侵染的作用。转基因植物导入干扰素在动物细胞中产生的环状AMP-非依赖蛋白激酶，表现出对立枯病、白粉病等病害的抗性。在这些转基因植株中，ATP含量显著增加。如上所述，似乎植物的抗病能力与磷代谢有着密切的关系。然而，细菌病害与磷酸盐代谢之间的关系并不是很密切，就火疫病(Pseudomonas syringae PV.)而言。Tabaci)病。从目前的实验结果来看，磷代谢与植物对病毒和真菌病害的抗性密切相关。

2,5-oligoadenylate synthease (2,5-AS) which induced in virus-infected animal cells forms 25-oligoadenytic acid [pppA(2p5A)n] from ATP.Transgenic plants (tobacco) introduced 2,5-AS gene showed resistance not only on viruses (cucumber mosaic virus and tobacco mosaic virus) but also on fungal diseases such as damping off which is cased by Rhizoctonia solani or powdery mildew disease which is caused by Erysiphe cichoracearum. The disease resistance was more promoted by treatment with phosphate salt (K- phosphate). The cell wall of the host plants treated with phosphate was thicker than that of untreated one. Thus, it was suggested that increase of resistance by treatment of phosphateis caused by inhibition of invasion by the fungi. In the transgenic plants with 2,5-AS gene, ribonuclease (RNase) activity increased more than in non-transgenic plants. The enzyme activity increased more by phosphate treatment, and it seemed also to act the inhibition of infection. The transgenic plants introduced cyclic AMP-non-depended protein kinase which produced in animal cells by interferon, showed resistance for diseases such as damping off and powdery mildew diseases. In these transgenic plants, ATP contents increased significantly. As mentioned above, it seemed that there are close relations between disease resistance and phosphate metabolism of plants. However, the relation between a bacterial disease and phosphate metabolism was not dear, so far as on fire blight (Pseudomonas syringae pv. tabaci) disease. From the present experimental results, it was confirmed that phosphate metabolism related closely to the plant resistance against virus and fungal diseases.