Effect Of Different Nitrogen Levels And Forms On The Growth And Metabolism In Isodon Rubescens

Nitrogen is an essential macronutrient element for plants,and also a component of important organic compounds such as amino acids,proteins,nucleic acids,pigments,etc.Nitrogen promotes the growth of plants and delays leaf senescence,which is essential for plant growth and material metabolism.The stems and leaves of Isodon are mainly used as medicine,which means nitrogen plays an important role in the formation of its yield and quality.In this experiment,Isodon was used as the experimental material,and the nutrient solution culture method was used to carry out different nitrogen levels（CK、1m M、3.75m M、7.5m M、15m M）and different nitrogen forms（CK;NO₃^-;NH₄⁺;NO₃^--NH₄⁺（50:50）;Urea;Gly;Glu）and different nitrogen ratios experiment[NO₃^--NH₄⁺（100:0;75:25;50:50;25:75;0:100）;NO₃^-:Gly（75:25）;NO₃^-:Glu（75:25）],from the aspects of growth and development,nitrogen metabolism,photosynthetic performance,physiological and biochemical indicators,active substance metabolism,combined with transcriptomics analysis,we systematically explored the absorption、the rules of transportation and the influence of different nitrogen forms on its yield and quality.The main experimental results are as follows:1.With nitrate nitrogen as the nitrogen supply in the nutrient solution,the experimental results of different nitrogen levels showed that in the range of 0-15 m M,the plant height,leaf area,photosynthetic performance and biomass of Isodon were positively correlated with the nitrogen level.There was no significant difference between 7.5m M and 15m M nitrogen levels.The nitrogen level of 3.75-7.5m M was more suitable for the synthesis of oridonin and rosmarinic acid.The concentration of oridonin was higher at the nitrogen level of 3.75m M,and the synthesis accumulation was the highest when the nitrogen concentration is 7.5m M;The concentration of rosmarinic acid and synthetic accumulation was the highest in the 7.5m M nitrogen level.Therefore,nutrient solution culture with 7.5 m M nitrogen supply is the most suitable for the growth of oridonin and the synthesis of oridonin and rosmarinic acid.2.The experimental results of different forms of nitrogen showed that nitrate nitrogen promoted the absorption of Ca,Mg,Fe,Cu and Mn ions by the roots,and improved the transport of K and Mg ions to the upper part of the ground,especially the leaves.And nitrate was conducive to plant growth,plant height,leaf area,net photosynthetic rate,chlorophyll SPAD,root development biomass,promoting the synthesis of oridonin,and also to the highest accumulation of oridonin,while the accumulation of rosmarinic acid was sutiable with the ammonium nitrate.Therefore,nitrate nitrogen is the most suitable for the growth of oridonin in nutrient solution culture,and ammonium nitrate is more conducive to the synthesis of rosmarinic acid.3.The experimental results of different nitrogen ratios showed that 100%NO₃^-and 75%NO₃^-+25%NH₄⁺were more conducive to the absorption of nitrogen and phosphorus and the transport to the aerial part of Isodon,especially the transport and distribution to the leaves,100%NO₃^-was most conducive to the absorption and distribution of potassium to the stem;NR and GS had the strongest activity under75%NO₃^-+25%NH₄⁺,while GDH under the conditions of 50%NO₃^-+50%NH₄⁺;100%NO₃^-and 75%NO₃^-+25%NH₄⁺treatments had the largest plant height,leaf area,photosynthetic performance,and biomass of Isodon;75%NO₃^-+25%NH₄⁺treatment promoted the synthesis of oridonin,but had the medium concentration;the supply of 100%NO₃^-was not conducive to the synthesis of rosmarinic acid,and the combined application of ammonium nitrogen and nitrate nitrogen was more conducive to the synthesis of rosmarinic acid,and the best effect is the ratio of50-75%NH₄⁺.In short,100%NO₃^-and 75%NO₃^-+25%NH₄⁺are more conducive to the growth of Isodon chinensis and the synthesis of oridonin,while the supply of100%NO₃^-is not conducive to the synthesis of rosmarinic acid,and 50-75%NH₄⁺is used in combination of nitrate nitrogen for the synthesis of rosmarinic acid.4.Transcriptome sequencing of the leaves and roots of Isodon vulgaris leaves and roots with 100%NO₃^-,100%NH₄⁺,75%NO₃^-+25%NH₄⁺,and the differentially expressed genes of leaves under the treatment of three different forms of nitrogen is1596,the pathways with genes are transporter activity,translation regulator activity,terpenoid metabolism,and nitrogen metabolism;the differential gene expression in the oridonin synthesis pathway was the most up-regulated in the total ammonium treatment group,75%NO₃^-+25%NH₄⁺The genes with larger ammonium up-regulation are DXS,IDI,CPS and KSL;the key genes of rosmarinic acid metabolism pathway 4CL5,HPPR,PAL,TAT are up-regulated by total ammonium treatment,and RAS,HPPR3,4CL are up-regulated by 75%NO₃^-+25%NH₄⁺has a larger up-regulation fold;nitrogen metabolism key enzyme GS has a larger fold of75%NO₃^-+25%NH₄⁺up-regulation;GDHA and GDH2 have a larger fold of up-regulation with total ammonium;there are 1803 significantly different gene expressions in the roots,which are enriched to nitrogen metabolism pathway;root nitrogen metabolism enzymes GS,GS1,GDHA,GDHB,GDH2 are up-regulated in total ammonium treatment,GS and GS1 remain unchanged under 75%NO₃^-+25%NH₄⁺treatment,and other genes are up-regulated trend.The results of this study provide a basis for revealing the law of nitrogen nutrition of Isodon Rubescens,and also lead a theoretical base and experimental foundation for the standardized cultivation and management of Isodon Rubescens.