Effects of mycorrhizal fungi on phytate-phosphorus utilization in trifoliate orange ( Poncirus trifoliata L. Raf) seedlings

We determined the phosphate (P) uptake, substrate P concentration, phytase activity, acid phosphatase activity and expression of three predicted secreted purple acid phosphatase genes ( PAP s) from trifoliate orange ( Poncirus trifoliata L. Raf) through Glomus versiforme and phytin treatments to evaluate phytate-phosphorus utilization promoted by arbuscular mycorrhizal fungi (AMF, G. versiforme ). The results showed that under inorganic phosphate (Pi) deficiency, trifoliate orange seedlings utilized phytin and G. versiforme colonization promoted trifoliate orange phytin utilization by increasing phytase activity and acid phosphatase activity in the roots and the substrate. Although the expression of the three secreted PtPAPs in the seedlings was significantly upregulated in the roots and the leaves after 2 months of −P solution application, the genes exhibited different expression patterns. In general, PtPAP1 was regulated more strongly in the roots than in the leaves, which was upregulated by G. versiforme colonization but downregulated by phytin treatment in the roots. PtPAP2 was activated by Pi deficiency in the leaves but was almost constitutive expressed in the roots. PtPAP3 , which might encode a phytase, was also regulated more strongly in the roots than in the leaves and reduced by phytin treatment, but unaffected by G. versiforme colonization. The expression patterns of the PtPAP genes in response to the AMF and organic phosphate (Po) treatments suggested that the three PtPAPs had different functions in the Po utilization of trifoliate orange. Although the phytase activity and acid phosphatase activity in the roots and the substrate were not consistent with PtPAPs expression, AMF promoted the activities of the two enzymes in the substrate, which was at least partly ascribed to the regulation of PtPAPs expression.