Dissection Of Ammonium Toxicity In China Fir-using Arabidopsis Thaliana As A Model System

Nitrogen is one of the necessary elements for plant growth and development,which is absorbed by plant as two main ways:the nitrate nitrogen(NO3-)biased by plant and ammonium nitrogen(NH4+).However,the nitrate nitrogen is easy to leaching loss,and with the industrial development,the nitrogen deposition becomes increasingly serve,resulting in the enrichment of ammonium nitrogen in soil,further leading to root maldevelopment,leaf chlorosis,even plant death,which will cause the yield reduction of forests and meadows and other problems.As a species with high speed growth,China fir(Cunninghamia lanceolata),ranks the first place in south of China according to it's planting area and the proportion of timber volume.Meanwhile,it suffers from a series of effects produced by high ammonium in soil,which damages its ecological and economic values.Up to now,the molecular mechanism of ammonium toxicity to plant is unclear,it only stays at the not widely agreed hypothesis level.Although both of China fir and A.thaliana are sensitive to high ammonium,previous study found that the intermediate substrates from TCA metabolic processing can relieve the ammonium toxicity.Therefore,5 kinds of substrates were added into the media with high ammonium treatment for both China fir and A.thaliana in this study,the result showed that the ammonium toxicity is alleviatived.To clarify the molecular mechanism of China fir ammonium toxicity,we screened the lines are resistant or sensitive to ammonium toxicity which is based on the abundant molecular and genetic information of model plant A.thaliana.One sensitive to high ammonium line was found from 50 thousands seeds(Col-0)induced by EMS under a certain ammonium treatment.Simultaneously,one line and 8 lines displaying resistance and sensitive to high ammonium respectively were acquired from 335 variable lines whose variant information is known.By detecting the relevant physiological indexes including metabolic and assimilative enzymes related to nitrogen and ammonium respectively,our findings indicate that the toxicity mechanism of high ammonium to plant is not closely correlation to metabolic efficiency of nitrogen,it may be related to other genes or pathways.