Study on enhancement of wide-range stress tolerance by rhizosphere control on moleculartolerance by rhizosphere control on molecular base.

酸碱土占世界耕地面积的一半以上。由于营养物的不溶性以及A1和重金属等无机化合物的毒性，这些土壤中的植物生长受到抑制。近年来，研究表明植物根系有一定的策略来改善根际环境（距离根表面约几μm）。研究了提高根际调节功能的能力。本研究结果总结如下：1)将白魔豆根分泌的LASAP2编码酸性磷酸酶的cDNA转化到烟草植株中。将含有启动子区的基因组DNA转化到水稻植株中。这些植物能够分泌酸性磷酸酶，其性质与天然露平根成熟蛋白基本相同。2)为将磷酸烯醇丙酮酸羧化酶（PEPC）基因导入水稻植株，设计了几种用于农杆菌转化的基因构建体。为了高效表达PEPC，我们选择了一个肌动蛋白启动子调控的PEPC基因转基因水稻品系。从水稻植株中分离到新的PEPC基因，并对其功能进行了分析。新型PEPC为C3型，在叶片中特异诱导。与根型PEPC的同源性约为80%。PEPC转基因水稻对A1和低磷的耐受性得到了提高，这是由于PEPC mRNA和蛋白的过度表达导致根系草酸分泌增加。3)研究了缺磷洋葱根系分泌物对丛枝菌根真菌菌丝生长的影响。用薄层色谱法从洋葱根渗出液的乙酸乙酯部位分离得到A1 （Rf:0.47）。将玛格丽塔Gigaspora margarita孢子在该馏分和去离子水（对照）中孵育7天。A1部分的外菌丝长度和二级以上分支数均高于对照。

Acid and alkaline soils occupy over half of arable land in the world. Plant growth is inhibited in these soils because of the insolubilization of nutrients and toxicity of inorganic compounds such as A1 and heavy metals. Recently, it is indicated that the plant roots have some strategy to improve the rhizosphere environment (about several μm from root surface). We have studied to increase the capacity of function for rhizosphere regulation. The results of this study are summarized as follows;1) A cDNA for LASAP2 encoding acid phosphatase secreted from white lupin roots was transformed into tobacco plants. Genomic DNA containing promoter region was transformed into rice plants. These plants were able to secrete the acid phosphatase which had mostly same properties with native mature protein of white lupin roots.2) To introduce the PEPC (phosphoenolpyruvate carboxylase) gene into rice plants, some gene constructs for transformation using Agrobacterium were designed. For the efficient expression of PEPC, a transgenic rice line containing PEPC gene under regulation of actin promoter was selected. Novel gene for PEPC was isolated from rice plant, and the function was analyzed. The novel PEPC was C3 type and specifically induced in leaves. The identity was about 80% with root type PEPC. The A1 and low P tolerances were improved in PEPC transgenic rice line because overexpression of mRNA and protein for PEPC causes the increase of oxalate secretion from roots.3) Effect of root exudates of P-deficient onion on hyphal growth of arbuscular mycorrhizal fungi were studied. A1 fraction (Rf:0.47) was isolated by TLC from ethyl acetate fraction of onion root exudates. Spores of Gigaspora margarita were incubated in this fraction and deionized water (control) for 7 days. Length of external hyphae and number of 2nd or higher order branches were higher in A1 fraction than in control.