Insoluble-Phytate Improves Plant Growth and Arsenic Accumulation in As-Hyperaccumulator : Phytase Activity, Nutrient Uptake, and As-Metabolism.

Phytate, the principal P storage in plant seeds, is also an important organic P in soils, but it is unavailable for plant uptake. However, the As-hyperaccumulator can effectively utilize soluble Na-phytate, while its ability to utilize insoluble Ca/Fe-phytate is unclear. Here, we investigated phytate uptake and the underlying mechanisms based on the phytase activity, nutrient uptake, and expression of genes involved in As metabolisms. plants were cultivated hydroponically in 0.2-strength Hoagland nutrient solution containing 50 μM As and 0.2 mM Na/Ca/Fe-phytate, with 0.2 mM soluble-P as the control. As the sole P source, all three phytates supported growth, with its biomass being 3.2-4.1 g plant and Ca/Fe-phytate being 19-29% more effective than Na-phytate. Phytate supplied soluble P to probably via phytase hydrolysis, which was supported by 0.4-0.7 nmol P min g root fresh weight day phytase activity in its root exudates, with 29-545 μM phytate-P being released into the growth media. Besides, compared to Na-phytate, Ca/Fe-phytate enhanced the As contents by 102-140% to 657-781 mg kg in roots and by 43-86% to 1109-1447 mg kg in the fronds, which was accompanied by 21-108% increase in Ca and Fe uptake. The increased plant As is probably attributed to 1.3-2.6 fold upregulation of P transporters for root As uptake, and 1.8-4.3 fold upregulation of arsenite antiporters for As translocation to and As sequestration into the fronds. This is the first report to show that, besides soluble Na-phytate, can also effectively utilize insoluble Ca/Fe-phytate as the sole P source, which sheds light onto improving its application in phytoremediation of As-contaminated sites.