Response Mechanism Of Tomato Seedlings To Ammonium Nitrogen

Nitrogen is very essential to the growth,yield and quality of crops.The scientific application of nitrogen plays a key role to in environmental quality and economic benefits.Ammonium nitrogen is one of the two forms inorganic nitrogen absorbed by plants.But for a long time,it has been thought that ammonium nitrogen could result in growth inhibition of most plants,especially for ammonium sensitive plants,but the mechanism is rarely reported.Tomato is one of the most popular crops,and it is also a "nitrate loving crop".Thus,F1 tomato "kui guan hong feng",which is the main cultivated varieties in local,was used in this study,and nitrate nitrogen was used as the control.The treatments were designed respectively,including 5,7.5,10,15,20mM single ammonium nitrogen,5,7.5,10,15mM single ammonium nitrogen under salt stress,and 15mM total nitrogen concentration of ammonium and nitrate,ammonium nitrogen ratio was 0,5,7.5,10,15mM.The root morphology,nitrogen utilization and assimilation efficiency,leaf photosynthetic capacity,chloroplast structure,nutritional metabolism,antioxidant metabolism and proteomics,were measured and analyzed,which were aimed to explore physiological and molecular mechanism of tomato seedings to ammonium nitrogen in.The main results were as follows:1.Ammonium nitrogen and the growth of tomato seedlings.Compared to the control,when ammonium concentration was less than 10mM,there were no significant difference in root length,total root surface area and total root volume,and in nitrogen use efficiency(NUE)related to root morphology.At the same time,there were no significant difference in chloroplast structure and quantity,the contents of chlorophyll and mineral elements of leaves,between treatments and the control.Under 10mM ammonium treatment,tomato roots began to become shorter and smaller,the dry root weight,total root surface area and biomass were decreased by about 20%,and the growth of tomato was inhibited slightly.However,when the ammonium nitrogen was 15 and 20mM,the indexs of root morphology were decreased by more than 30%,while chloroplast structure was destroyed,and grana lamellae was disintegrated,which resulting in the decrease of net photosynthetic rate by more than 30%,the decrease of biomass by more than 39%,and growth was significantly inhibited.In addition,when nitrate nitrogen was added,the total dry weight were increased by 27% and 20% under 5mM and 7.5mM ammonium nitrogen ratio treatments,was decreased by 14% under 10mM ratio treatment,and was decreased by 22% under 15mM ratio treatment.2.Ammonium nitrogen and N metabolism in tomato roots and leaves.Compared to the control,under ammonium nitrogen,the total nitrogen content was increased by 9%-37%,the efficiency of nitrogen absorption(NUp E)was increased by 15%-28%.The activities of glutamine synthetase(GS),glutamate synthetase(GOGAT)and glutamate dehydrogenase(GDH)involved in nitrogen metabolism in roots were significantly higher than those in the control.The contents of total free amino acids were more than 2 times that of the control in roots,and were increased by 40%-96% in leaves.The contents of asparagine(Asn)and glutamine(Gln)also were increased significantly.The increase of total nitrogen content,NUp E,and amino acids content,resulting the significant increase of protein content.At the same time,proteomics data also showed that the expression of K4BPV5 and K4D9J3,which promoted ammonium assimilation,were up-regulated.These results showed that ammonium nitrogen has promoted ammonium assimilation.3.Ammonium nitrogen and photosynthetic carbon assimilates in tomato.Compared to the control,under 5mM and 7.5mM ammonium nitrogen,the contents of soluble sugar and starch were increased by more than 33% in roots and leaves,and the contents of nitrogen element,compounds of nitrogen,and other mineral elements in leaves,were higher,which promoted the synthesis of chloroplast and chlorophyll.Transmission electron microscopy of chloroplast also showed that compared to the control,the structure of chloroplast was clear,the number were 1.51 and 2.04 times under 5mM and 7.5mM ammonium nitrogen,and the number of basal grains was 1.5 times under 7.5mM ammonium nitrogen,grana thickness andgrana lamellae number were similar to the control.At the same time,the chlorophyll content was high,and the photochemical quenching coefficient(qp)and the actual photochemical efficiency((37)PSII)did not change significantly.In addition,the stomatal conductance(gs),intercellular CO2 concentration(Ci)in leaves did not change significantly compared to the control.These results indicated that the photosynthetic carbon assimilation ability and the content of photosynthetic product starch were promoted under the appropriate ammonium nitrogen concentration.4.The effects on ammonium nutrition and plant stress resistance.Compared to the control,under 5m M and 7.5mM ammonium treatment,the biomass of plants were increased by 21% and 43%,respectively,and the contents of reactive oxygen(ROS)and malondialdehyde(MDA)in roots and leaves were decreased significantly.The contents of osmotic regulators and antioxidants were measured,and the results showed that the content of soluble proteins was increased significantly,ascorbic acid/dehydroascorbic acid(As A/DHA)was increased by more than 35%,reduced glutathione/oxidized glutathione(GSH/GSSG)was increased by more than 38%.While the activities of ascorbate peroxidase(APX),glutathione reductase(GR)and dehydroascorbic acid reductase(DHAR)were enhanced significantly.Proteomics data analysis showed that glutathione metabolic pathway was changed under ammonium nitrogen,the molecular functions related to antioxidant activity and oxidoreductase activity,and cell components related to peroxidase,were changed.In addition,three differential proteins(DEPs:H6WYS2,K4C2K4,K4BK60)related to the encoding metalloproteinase of chloroplasts were found.5.Excessive ammonium nitrogen and plant growth inhibition.Under 15mM and 20mM ammonium nitrogen,we found mineral nutrients were deficient and chloroplast structure was damaged in leaves.With the destruction of chloroplast structure,grana lamellae was disintegrated and the number was decreased,the number of chloroplast was decreased by 32% and size was decreased by 42%,chlorophyll content was decreased by more than 40%.At the same time,gs,Ci,qp,(37)PSII,were decreased significantly,Non-photochemical quenching coefficient(NPQ)was increased significantly.So photosynthetic carbon assimilation ability was decreased significantly,and the starch content of photosynthetic product was decreased significantly,and NUt E was decreased.However,the NUp E and total nitrogen content were still at a high level,leading to the accumulation of NH4+.At the same time,proteomics data showed that biology processes related to carbon utilization,nitrogen utilization,chloroplast and stomatal movement were changed,and pathways of nitrogen metabolism,starch and sugar metabolism,were changed.Proteins Q5NE21 and K4CV84,B5M9E4,K4BKF6,K4BBT6,were down-regulated.In addition,proteomics analysis also showed that DEPs related to cell wall was down-regulated and the pathway of phenylpropionic acid metabolism related to cell wall synthesis was changed.The conclusion: The tomato F1 "kui guan hong feng" can grow normally under single ammonium nutrition,10mM is critical point of growth,even if there is nitrate nitrogen.When ammonium concentration in less than 10mM,the plant grown well,the total nitrogen content,absorption and assimilation capacity of nitrogen,the contents of amino acids and proteins,were at high level.The structure of chloroplast was integrity,the quantity of chloroplast was more,the photosynthetic parameters and mineral element contents were well,resulting in the balance between nitrogen metabolism and carbon metabolism in the plant,the growth of roots and leaves were well.At the same time,under the appropriate concentration of ammonium nitrogen,NH4+ triggered the change of As A/GSH circulatory metabolism system and proteins related to chloroplast metalloproteinase,and participated in the change of ROS signal metabolism,improving the antioxidant capacity of plants.When the concentration of ammonium nitrogen was higher than 10mM.Proteins Q5NE21,and K4CV84,B5M9E4,K4BKF6,K4BBT6 were down-expression,and the damage of chloroplast structure and the loss of mineral elements,and so on,which resulted in the decrease of photosynthetic carbon assimilation capacity,the lack of carbon source for ammonium assimilation and the imbalance of C and N metabolism,so,the growth of plants was inhibited.In addition,the inhibition may be related to the lignification of cell wall caused by the change of phenylpropanoid metabolic pathway.