Character Of Phosphate Soublizing Of Piriformospora Indica And Effects On Phosphours Absorption In Brassica Naups

Rapeseed is one of the main cultivated oil crops in China.Brassica napus L is the dominant variety.This variety has been shown to be sensitive to the phosphorus nutrient.Most of the cultivation area of this rapeseed variety lies within the region with low phosphorus content.Therefore,the improvement of phosphorus utilization efficiency becomes critical for the sustainable production of rapeseed.Piriformospora indica is a newly discovered plant symbiotic fungus,which has been shown to be able to promote plant root growth and enhance plants’ resistance against abiotic and biotic stress.It would be of great practical significance to investigate whether Piriformospora indica could be employed to the phosphorus use efficiency in rapeseed.In this study,we investigated the effect of Piriformospora indica on phosphorus dissolvement in the medium and its effect on pH value.Our results showed that Piriformospora indica is able to dissolve tricalcium phosphate(Ca3-P)and almunium phosphate(Al-P)and alters the pH value.The amount of dissolved phosphorus tends to be associated with the pH value.Orthogonal experiments were conducted with different carbon sources,nitrogen sources and pH value.The optimal condition was found to be 10.0g soluble starch with 0.5 g calcium nitrate at pH 8.0.Ferric phosphate(Fe-P)could be solubilized only in the modified medium.Ca3-P is the easiest dissolved phosphorus nutrient,followed by Al-P and then by Fe-P.The amount of dissolved phosphorus for the above three phosphorus nutrient is 178.32 mg/L,149.48 mg/L and 54.17 mg /L,respectively.We further investigated the phosphorus uptake efficiency of B.napus under different insoluble phosphorus sources.Compared to the control treatment,plants inoculated with Piriformospora indica displayed growth and development with all the three phosphorus sources(aluminum phosphate,tricalcium phosphate and iron phosphate).The fresh and dry root weight increased by 4.3-48.7%.Leaf area increased by 19.0-21.3%.The chlorophyll content of the inoculated plants is 3.0-20.3% higher than the control plants,with 8.2-9.2% increase in the photosynthesis level.The activity of acid phosphatase in the roots is 1.3-2.5 times of that in the control plants.In addition,the available phosphorus concentration in the soil rhizosphere are 1.3-4.8 times of the control.Oxalic acid,malic acid and citric acid concentrations in rhizosphere increased 1-5.4 times based with different phosphorus sources.Our results also showed that the expression of the acid phosphatase and phosphate transportation related genes BnACP5 and BnPht1 increased by 7.1-34.5 times and 4.6-10.4 times respectively upon inoculation(P <0.05).The content of phosphorus in the shoots and roots increased by 8.1%-34.3% and 3.0%-96.0% respectively.The effects of P.indica on the growth and phosphorus uptake of B.napus under low phosphorus stress(5 μM KH2PO4)were also investigated.We found that,upon Piriformospora indica inoculation,shoot and root fresh weight of Piriformospora indica increased by 29.8-68.2% under normal phosphorus concentration(1 mM)and low phosphorus(5 μM).Phosphorus content in the shoots and roots increased by 60-80%.The expression of phosphorus stress related genes BnACP5,BnPht1;4,BnPT2 and BnSPX1 are up-regulated in the leaves but suppressed in the roots.