Arsenic-hyperaccumulator Pteris Vittata Efficiently Solubilized Phosphate Rock By Secreting Phytic Acid To Sustain Plant Growth And Arsenic Uptake

Phosphorus(P)is one of the most limiting nutrients for plant growth in agricultural production for its low availability in soils.With the increase of population and demand of farm products,more P minerals,especially phosphate rock,are mined and manufactured into P fertilizers which are applied in agricultural soils in quantity.Based on the background,many studies focus on how to improve efficiency of P utilization by crops.In this study,arsenic(As)hyperaccumulator Pteris vittata was efficient in acquiring P from insoluble phosphate rock(PR),which is difficult for crop plants to utilize.Although its unavailability,phosphate rock is the raw materials of P fertilizers and not leaching into water body to cause eutrophication,which is a superior choice of P fertilizer.When supplemented with PR as the sole P source in a hydroponic system,P.vittata accumulated 2228 and 2605 mg kg-1 P in its roots and fronds,49%and 28%higher than 1493 and 2039 mg kg-1 in-P treatment.Moreover,the P contents in P.vittata tissues were comparable to 2075 and 2662 mg kg-1 in P treatment.In order to make a comparison,a non-hyperaccumulator Pteris ensiformis was carried out in the same experimental condition.The results indicated that P.ensiformis was unable to solubilize P from PR,indicating that this property was not universal in ferns.To gain insights into the mechanisms in PR solubilization by plants,organic acids in plant root exudates were analyzed by HPLC-UV and TOF-MS.The results showed that phytic acid was the predominant organic acid in P.vittata root exudates,accounting for>90%,whereas only oxalic acid was detected in P.ensiformis root exudates.Moreover,P.vittata secreted phytic acid at 674 and 697 mg kg-1 root DW h-1 in-P and PR treatments,?9 fold higher than that in P treatment.Phytic acid was a unique organic acid in P.vittata root exudates which was more effective in solubilizing PR,as it released 49?87%more P than oxalic acid at 10?500 ?M compared to oxalic acid,suggesting that phytic acid was critical for P acquirement from PR by P.vittata.P.vittata often grows in As-contaminated soils with arsenate[As(V)]being the dominant As species in soils.As an analogue,As(V)competes for P uptake and interferes with P metabolism in plants.Therefore,to better understand P mobilization and uptake,the effects of As(V)on phytic acid secretion,PR solubilization and P acquisition by P.vittata and P.ensiformis were investigated.The presence of arsenate decreased oxalic acid secretion by 50%in P.ensiformis roots,but it did not inhibit phytic acid secretion or P uptake in P.vittata.As a result,P.vittata could normally utilize phosphate rock by phytic acid efficiently even under As(V)stress,but P.ensiformis could not.Our data indicated that phytic acid played an important role in efficient use of insoluble PR by P.vittata,shedding light on using insoluble PR as P fertilizer and increasing crop P uptake in soils,and to enhance phytoremediation of As-contaminated soils.