Investigation and application of adaptation strategies of plant roots to acid soil.

本研究旨在解决酸性土壤作为耕地利用的问题。酸性土壤的关键问题是1)金属离子的毒性和2)磷饥饿。一些植物物种已经制定了一些适应酸性土壤的策略。我们已经证明，几种根分泌物对酸性土壤上的胁迫具有耐受性。因此，本研究对植物根的分泌能力进行了研究。将从白羽扇豆中分离到的分泌型酸性磷酸酶基因导入烟草中，该基因被认为是耐磷植物。从野生型植株获得的转基因植株的生长和磷的吸收都得到了改善。为了研究有机酸的分泌能力，将无机磷从难溶的形式中释放出来，以拟南芥的苹果酸分泌物为模型。这表明苹果酸转运蛋白的上调诱导了苹果酸的释放。苹果酸转运蛋白…的诱导表达铝胁迫更多地存在于根尖和根内组织中，表明铝的作用机制受到调控，从而使碳耗降到最低。因此，提高植物对无机磷的吸收能力需要对转运蛋白进行定点调控，不同植物根分泌物中由多糖组成的粘液的特性是不同的。三价阳离子与二价阳离子的亲和力最高，而玉米与三价阳离子的亲和力最高。虽然粘液的结合强度远低于玉米，但对铝离子的亲和力较高。推测对阳离子的吸附专一性差异不仅与糖的组成有关，还与糖醛酸的甲基化有关。对菌根菌丝伸长相关物质进行了分离纯化。成功地从洋葱根分泌物中获得了诱导菌根菌丝伸长和二次分枝的A2组分。较少

This study aimed to solve problems on acid soils for utilization as arable soils. Critical problems of acid soil are 1) toxicity of metallic ions and 2) phosphorus starvation. Some plant species have been developed some strategies to adapt on acid soils. We have shown that the several root exudates bring the tolerance to stresses on acid soils. Therefore, the secreting abilities of plant roots were investigated in this study.A gene for secretory acid phosphatase isolated from white lupin, which is well known as a phosphorus tolerative plant, was introduced into tobacco plants. The growth and phosphorus acquisition of transgenic plant were improved from wild type plants. To investigate the secreting ability of organic acid, which can liberate inorganic phosphate from sparingly soluble forms, malate exudation of Arabidopsis was chosen as a model. It was indicated that malate release was induced by the up-regulation of malate transporter protein. The induction of malate transporter expres … More sion by aluminum was specific in the root tips and internal tissues of roots, suggesting that the mechanism is regulated to minimize the carbon consumption. It is concluded that site-specific regulation of the transporters is required to improve the inorganic phosphate uptake ability.It was suggested that the specificities of mucilage, consisted of polysaccharides, in the root exudates differed among plant species. The highest affinities of mucilage of Melastoma malabathricum and maize were shown with trivalent and divalent cations, respectively. The affinity of mucilage of Melastoma malabathricum was high to aluminum ion, though the binding strength was quite lower than that of maize. It was supposed that not only the composition of sugar but also methylation of uronic acids were involved in the differences of adsorption specificity to the cation. Separation and purification of substances involved in the elongation of mycorrhizal hyphae was conducted. It was succeeded that an A2 fraction, which induced an elongation and secondary and further branching of mycorrhizal hyphae was obtained from root exudates of onion. Less