| Phosphorus(P)is essential to plant growth and development,and thus plays a crucial role in plant metabolic activity.However,phosphate(Pi)is easily fixed by soils due to its physical and biochemical properties,and thus difficult to be acquired and utilized by plants.It has been documented thatacid phosphatase(APase)participates in organic-P utilization,but its temporal and spatial dynamic expression patterns responsive to Pi starvation remained largely unknown in plants.In the present study,dynamic changes of soluble Pi concentration and APase activity were investigated in different organs or tissues of soybean at vegetative and reproductive stages.Subsquently,two purple acid phosphatases(PAPs),Gm PAP8 and Gm PAP17,were selected for examin ing their expression patterns,subcellularlocalization and enzymatic properties.The main results were shown as followings:1.Phosphorus deficiency significantly decreased soluble Piconcentrationsin different organs or tissues at different developmental stages,compared with that under normal conditions.At the young seedling stage,soluble Pi concentrations in primary leaves,cotyledons and roots were significantly decreased by P deficiency,especially in roots,which soluble Pi concentration was reduced by 64%.Furthermore,with increased time of low P treatment,the most dramatic decreases of soluble Pi concentrations was observed in roots,at 12 days of low P treatment,its soluble Piconcentration was reducedby 94%,compared with that under normal phosphorus conditions.At the reproductive stage,phosphorus deficiency also significantly reduced soluble Pi concentration in young leaves,old leaves,roots,podshells and seeds.Among them,the reduction of soluble Pi concentration in roots was the most dramatic,as reflected by 89% reduction.Among all the tested tissues or organs,the leastreduction in seed soluble Pi concentration was observed,as reflected by decreases of 67% in small seeds(at flowering and podding stage),40% in big seed(at flowering and podding stage),65%(at seed formation stage)and 51%(at seed mature stage),respectively.These results suggest thatchanges of root soluble Piconcentrationwas the most dramatic by Pi starvation,but changes of seed soluble Pi concentration was the least.2.Phosphorus deficiency significantly affected APase activitiesin different tissues or organs at different development stages.After 3 days of P deficiency,P deficiency significantly increased APase activities in primary leaves,cotyledons and roots,which wasincreased by 0.5 times,1.2 times and 1.2 times respectively.Furthermore,with increased treatment time,APase activitiesinprimary leaves and roots were continuously increased byP deficiency.After18 days of P deficiency,compared to those under normal conditions,APase activities in primary leaves and roots were increased by 7.5 times and 6 times,respectively.However,changes of APase activities in cotyledons was initiallyincreased,and subsquently dereased by P deficiency,which led to no significant difference between two P treatments after 18 days of P deficiency.Atreproductivestage,phosphorus deficiencyonlysignificantly increased APase activities in young leaves and old leaves at the flowering and podding stage,podshells and seedsatseed formation stage.But phosphorus deficiency had no effect on APase activities in rootsat flowering and podding stage,in podshells and seedsat other stages.3.There are 38 members of the PAP family in the soybean genome.Phylogenetic tree analysis showed that GmPAP8 and GmPAP17 had the highest similarity with the previously reported PvPAP3,which was 97% and 91%,respectively.However,atdifferent growth and development stages of soybean,phosphorus deficiency had different effects on expression patterns of Gm PAP8 and Gm PAP17 in different organs or tissues.At vegetative stage,after 12 days of P treatments,phosphorus deficiency significantly increased their expression inprimary leaves and roots respectively.At flowering and podding stage,phosphorus deficiency significantly increased expressions of Gm PAP8 and Gm PAP17 in young leaves,old leaves and roots.But Pi starvation decreased expression was observed forGm PAP8 in podshells at flowering and podding stages,and in seeds at seed formation stage,for Gm PAP17 in seeds at flowering and podding stage,and in pod shells at seed formation stage,respectively.These results suggestedeffects of P deficiency onGm PAP8 and Gm PAP17 expression patterns were variousin differntsoybeanorgans or tissues,indciating that they mighthave different biological functions.4.Hydrolysis activity of recombinant GmPAP8 and GmPAP17 was also separately investigated.Results showed that GmPAP8 exhibited high activity against ρ-NPP and phytate.Furthermore,relative activity of GmPAP8 against phytate toρ-NPP was 92.9%.However,GmPAP17 exhibited activity against 7 kinds of substrates,incdluing ρ-NPP,dNTPs,ATP,d TTP,CTP,ADP and GTP.Furthermore,relative activity of GmPAP17 against other substrates to ρ-NPP was more than 100%,respectively.In summary,phosphorus availabilitysignificantly affected soluble Pi concentrations and APase activitiesinsoybean different organs or tissues atvegetative and reproductivestages,suggestingthat different capability of maintaining P homeostasis presents in different soybean tissues or organs.Furthermore,expression patterns ofGm PAP8 and Gm PAP17 were different in soybean responsive to p deficiency,suggestingthat they might have different biological functions. |
