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

本研究旨在解决酸性土壤开发利用中存在的问题。酸性土壤的关键问题是1)金属离子的毒性和2)磷饥饿。一些植物已经发展出适应酸性土壤的策略。结果表明，几种根系分泌物对酸性土壤具有较强的抗逆性。因此，本研究对植物根系的分泌能力进行了研究。将一株分泌酸性磷酸酶的基因引入烟草植株中，该基因是从一种著名的耐磷植物白豆中分离出来的。在野生型植物的基础上改良了转基因植物的生长和磷的获取。为了研究有机酸的分泌能力，以拟南芥的苹果酸分泌为模型，研究了有机酸的分泌能力。结果表明，苹果酸盐的释放是由苹果酸转运蛋白的上调引起的。铝对苹果酸转运蛋白表达的诱导作用主要集中在根尖和根内组织，表明铝对苹果酸转运蛋白表达的调控机制是为了减少碳的消耗。因此，需要对转运蛋白进行位点特异性调控以提高无机磷酸盐的吸收能力。结果表明，不同种类植物根系分泌物中含多糖的粘液的特异性存在差异。三价阳离子和二价阳离子分别对褐霉黏液和玉米黏液具有最高的亲和性。malabathricum的黏液对铝离子的亲和力较高，但与玉米的结合强度较低。推测糖的组成和糖醛酸的甲基化对阳离子吸附特异性的差异不仅与糖的组成有关，而且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。结果表明，从洋葱根分泌物中获得了能诱导菌根菌丝伸长和次生分枝的A2组分。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