Phosphorus (P) deficiency increased the secretion of phytases from roots of various plant species. The secretory phytases were collected with a dialysis membrane tube for 24 hours from roots of sixteen plant species grown with low or adequate supply of P in nutrient solutions. The activity of not only secretory phytase, but also acid phosphatase, increased with the low P treatment in all of the plant species examined. Secretion of phytase by the roots under P-deficient conditions was highest in Brachiaria decumbens CIAT 606, Stylosanthes guianensis CIAT 148 and tomato, moderate in Brachiaria brizantha CIAT6780, Stylosanthes guianensis CIAT 2950, Alfalfa, white clover and orchard grass, and lowest in Andropgon gayanus CIAT 621, Stylosanthes capitata CIAT 10280, upland rice, timothy, redtop, alsike clover, red clover and white lupin plants. SDS-PAGE and immunoblotting analysis showed that the phytases with molecular weight of 35-40 kD could be detected in seven of the sixteen plant species tested. These results indicate that the secretory phytase may provide an efficient mechanism for certain plants to utilize inositol hexaphosphate in soil.

本文选择低磷耐性较强的羽扇豆和低磷耐性较弱的番茄两种作物，在不同磷水平下水培，对其根系分泌特性进行了比较研究。结果表明，在低磷条件下，羽扇豆酸性磷酸酶和有机酸分泌能力比番茄高2-3倍。番茄体内磷的生理临界浓度显著比羽扇豆为高，可能是其低磷耐性较低的重要原因。

Phytase (myo-inositol hexakisphosphate phosphohydrolase; EC 3.1.3.8) was purified from roots of tomato plants grown under phosphorus-deficient conditions using five purification schemes. The hytase was successfully separated from the major acid phosphatase to an eletrophoretic homogeneity. The native molecular weight of this enzyme was estimated to be about 164 kD by Bio-Gel P-200 gel filtration. The molecular weight of the subunit on SDS-PAGE was approximately 82 kD, indicating that the native form of the enzyme was a homodimer. The isoelectric point of tomato phytase was about 5.5. The enzyme exhibited a high affinity for phytic acid (Km=38μM), and was strongly inhibited by phosphate, molybdate and fluoride. Among other characteristics of tomato phytase, the pH and temperature optima were 4.3 and 45℃, respectively. Tomato phytase contained a fairly high concentration of aspartic, glutamic acid and glycine residues.

The distribution of secretory acid phosphatase and organic acids enhanced by phosphorus deficiency in lupin rhizosphere was investigated using a rhizo-box system which separated the rhizosphere soil in 0.5mm fractions. In the soil fraction closest to the root surface, the lupin exudates displayed an acid phosphatase activity of 0.73ug dry soil-1 and citrate concentration of 85.2μmole⋅g dry soil-1, respectively. The increase of the acid phosphatase activity induced an appreciable depletion of organic P in the rhizosphere, indicating that lupin efficiently utilized the organic P from soil through the enzyme activity. The sterile treatments demonstrated that the acid phosphatase in the rhizosphere was mainly derived from lupin root secretions. The secretory organic acids enhanced considerably the solubility of the inorganic P in three types of soil and a sludge. However, the secretory acid phosphatase and organic acids from lupin roots were only detected in a considerable amount in 0-2.5mm soil fractions from root surface.

Phyt1 gene was successfully transferred into soybean (Glycine max L. Merr. c.v. Jilin35, China) by Agrobacterium mediated method in this study. The results of molecular detections (Southern, Nouthern and Western) demonstrated that the phyt1 transgene was expressing in the transgenic soybean plant To and T1 generations, thereby caused a higher phytase activity and a lower phytate content in the ransgenic plants. This study is the first report about the transgenic soybean plants containing lower phytate.