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

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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