Richardson A E, Hadobas P A, Hayes J E
CSIRO, Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia.
Plant J. 2001 Mar;25(6):641-9. doi: 10.1046/j.1365-313x.2001.00998.x.
Phosphorus (P) deficiency in soil is a major constraint for agricultural production worldwide. Despite this, most soils contain significant amounts of total soil P that occurs in inorganic and organic fractions and accumulates with phosphorus fertilization. A major component of soil organic phosphorus occurs as phytate. We show that when grown in agar under sterile conditions, Arabidopsis thaliana plants are able to obtain phosphorus from a range of organic phosphorus substrates that would be expected to occur in soil, but have only limited ability to obtain phosphorus directly from phytate. In wild-type plants, phytase constituted less than 0.8% of the total acid phosphomonoesterase activity of root extracts and was not detectable as an extracellular enzyme. By comparison, the growth and phosphorus nutrition of Arabidopsis plants supplied with phytate was improved significantly when the phytase gene (phyA) from Aspergillus niger was introduced. The Aspergillus phytase was only effective when secreted as an extracellular enzyme by inclusion of the signal peptide sequence from the carrot extensin (ex) gene. A 20-fold increase in total root phytase activity in transgenic lines expressing ex::phyA resulted in improved phosphorus nutrition, such that the growth and phosphorus content of the plants was equivalent to control plants supplied with inorganic phosphate. These results show that extracellular phytase activity of plant roots is a significant factor in the utilization of phosphorus from phytate and indicate that opportunity exists for using gene technology to improve the ability of plants to utilize accumulated forms of soil organic phosphorus.
土壤磷（P）缺乏是全球农业生产的主要限制因素。尽管如此，大多数土壤中含有大量的总土壤磷，这些磷以无机和有机组分的形式存在，并随着磷肥的施用而积累。土壤有机磷的主要成分是植酸盐。我们发现，在无菌条件下于琼脂中生长时，拟南芥植株能够从一系列预计存在于土壤中的有机磷底物中获取磷，但直接从植酸盐中获取磷的能力有限。在野生型植株中，植酸酶占根提取物总酸性磷酸单酯酶活性的比例不到0.8%，且未检测到其作为胞外酶的存在。相比之下，当导入来自黑曲霉的植酸酶基因（phyA）时，供应植酸盐的拟南芥植株的生长和磷营养状况得到显著改善。只有通过包含来自胡萝卜伸展蛋白（ex）基因的信号肽序列将黑曲霉植酸酶分泌为胞外酶时，它才有效。在表达ex::phyA的转基因株系中，根总植酸酶活性增加了20倍，从而改善了磷营养状况，使植株的生长和磷含量与供应无机磷酸盐的对照植株相当。这些结果表明，植物根的胞外植酸酶活性是利用植酸盐中磷的一个重要因素，并表明利用基因技术提高植物利用土壤有机磷积累形式的能力存在机会。
