The Molecular Physiological Mechanism Study Of Cadmium Accumulation Affected By Internal Or External Phosphate Status And Phosphate Starvation Signaling In Rice

Soil cadmium?Cd?pollution and excessive application of phosphorus?P?fertilizer are two serious problems existing in agricultural production.Reducing the application of phosphorus fertilizers and enhancing the phosphate?Pi?utilization efficiency of crops are significant for the sustainable development of agriculture.However,whether it will increase the risk of cadmium accumulation in crops remains obscure.In order to elucidate this relationship,the rice plants of wild-type?WT?,Pi-starvation signalling inhibited mutant?phr2?and Pi-over accumulated transgenic line?PHR2-OE?were chosen for research.To analyze the possible interactions between Pi and Cd signals,and the effects of external/internal Pi-staus and Pi-starvation singnal on Cd accumulation in rice,all plants were respectively grown in the solutions of Pi-sufficient?HP?and Pi-deficient?LP?with exogenously added Cd.Furthermore,the effect of Pi supply on Cd uptake rate in rice root was analyzed through the non-invasive micro-measurement technology.Finally,the effect of Pi-status on Cd accumulation was analyzed.The main results and conclusions are as follows:?1?Cd-stress affected the total P content and Pi-starvation signaling in WT plants.Our study showed that the P content in the shoot of WT was increased under the condition of HP/+Cd.Cd stress repressed the expression of OsIPS1,OsPT6 and OsPT10 in shoot under both the HP and LP conditions.Cd stress induced the expression of OsIPS1,OsPT6 and OsPT10 in root under HP condition,while had no significant effect on the expression of OsIPS1,OsPT6 and OsPT10 in root under LP condition.These results indicate that Cd stress can induce the Pi-starvaton signaling in root under HP condition,which may increase the uptake and transport of Pi,leading to the increase of P content in shoot.?2?The Cd accumulation and biomass inhibition ratio of Cd-stress were not obviously affected by external/internal Pi-status and Pi-starvation signal.Cd-stress significantly inhibited the biomass of WT,phr2,and PHR2-OE plants.However,statistical analysis of the inhibition ratio of Cd-stress on biomass showed that there was no significant difference for the Cd-stress resulted inhibition ratio between HP and LP condition in the plants of WT,phr2,and PHR2-OE.?3?External/internal Pi-status and Pi-starvation signal had no effect on the expression of the OsNramp5.Although low phosphate stress can significantly inhibit the expression of OsIRT1 and OsIRT2under LP condition in root,little repression for OsNramp5 was observed.?4?The external Pi-status does not affect Cd²⁺absorbtion in the plant root.No significant difference can be detected with the Cd²⁺uptake velocities under the+P and-P.Together,Cd-stress may affect the root Pi signal to promote shoot Pi-accumulation in WT.While the external/internal Pi-status has no significant effects on the Cd accumulation in rice.Therefore,reducing phosphate feritilizer application would not increase the risk of Cd accumulation in rice.