Improvement Of Nitrogen Absorption And Utilization In Rice By Aquaporin OsPIP1;2

In recent years,problems caused by the application of large amounts of nitrogen fertilizer have emerged in the agricultural practice.Excessive nitrogen fertilizer has led to the decline of nitrogen use efficiency and eutrophication.However,fertilizer is still indispensable to improve agricultural production.Therefore,gene engineer is a new method to seek high nitrogen use efficiency of crop species to absorb and utilize nitrogen fertilizers.Rice is one of the main crops in China.In the past 30 years,rice yield has increased dramatically.However,the problem of low use efficiency of nitrogen fertilizer still exists.Therefore,to explore the rice genes,which can improve nitrogen use efficiency under high input of nitrogen fertilizer,is improtant to screen the new genotypes of rice species.In general,plants need to keep the total carbon and nitrogen balance.In many cases,enhanced carbon assimilation acquires the nitrogen,vice versa,increase of nitrogen uptake and assimilation also needs more carbon skeleton.Otherwise,the over accumulation of nitrogen in plants causes negative effect on plant growth.In this study,we investigated an aquaporin OsPIP1;2,which is over expressed in rice,and its effect on the nitrogen uptake and use efficiency.We hypothesize that OsPIP1;2 may contribute to the nitrogen use efficiency in rice,because the OsPIP1;2 overexpression rices showed higher transport rate of CO2 and higher assimilation capacity of carbon.Our previous studies have found that OsPIP1;2 gene can improve the ability of rice to transport CO2 through the plasma membrane of mesophyll cells and overexprssion of OsPIP1;2 contributed to the absorption and transportation of CO2 in rice leaves.Therefore,this study explored the effect of overexprssion of OsPIP1;2 on nitrogen uptake and utilization in rice under various concentration of ammonium nutrition in hydroponic systems and under various input of nitrogen fertilizer in field conditions.The results are as follows:1.The OsPIP1;2 expression was significantly up-regulated in leaves and roots under high ammonium concentration.2.Compared with wild-type OsPIP1;2 over-expression lines has higher biomass,leaf area,root growth and proton secretion rate.The carbon and nitrogen content in OsPIP1;2 over-expression rice after 4 weeks cultivation was higher than wild type.However,the C/N ratio in different organs is relatively stable.3.Under 4 mM ammonium treatment,the wild type appeared ammonium toxicity symptom with inhibited growth,while OsPIP1;2 overexpression lines still maintained optimal growth with increase of biomass under enhanced ammonium concentration in nutrition solution.Under high concentration of ammonium,the proton secretion rate of root tips increased.And OsPIP1;2 overexpressing lines had stronger ammonium uptake and utilization ability than wild type.4.In the field experiment,OsPIP1;2 overexpressing lines showed higher yields with the increase of nitrogen application rate,and higher nitrogen use efficiency,indicating OsPIP1;2 caused improved nitrogen uptake and utilization of rice.In conclusion,rice aquaporin gene OsPIP1;2 may improve rice nitrogen utilization efficiency due to the higher photosynthetic capacity and carbon assimilation rate,which in turn enhanced nitrogen uptake.In addition,overexpression of OsPIP1;2 also enhanced root growth and development,proton secretion rate from root tips,which is important for the ammonium uptake and assimilation.This may be also the reason for the improvement of nitrogen use efficiency under higher input of nitrogen fertilizer in paddy fields.