The Response Of XTHs And Expansins To Different Aluminum Concentration In Roots Of Tea Plant (Camellia Sinensis (L.) O.Kuntze)

Aluminum?Al?toxicity is the main limiting factor for plant growth in acid soils,very low concentration of aluminum inhibits root growth in most plants.Tea plant?Camellia sinensis?is a typical Al-accumulating and Al resistance plant,which not only is not toxic to the growth of tea plants,but also can promote the growth and development of root system of tea plants.However,it is not clear how a certain concentration of aluminum can promote the growth of tea roots.The root growth of tea plants depends on the expansion and recombination of root cell walls,and XTHs and Expansins proteins are the most important proteins in this process.Are there differences in Expansins and XTHs protein activity and gene expression in tea root system under different aluminum concentrations?Will it affect the growth of tea root system?There are few reports of this kind of research.Therefore,in this study,the activity of XET and Expansins protein and the expression of corresponding coding genes in tea roots were determined under different aluminum concentrations,and the phenotype of root growth in tea plants were analyzed.To explore the response mechanism of XTHs and Expansins proteins and related genes expression to aluminum in tea root system,and to provide theoretical basis on clarifying the promoting mechanism of aluminum to tea root system growth.The main research results are as follows:1.The results of solution culture experiments of Longjing 43 and Baiye 1 tea plants showed that the response of tea plants to different aluminum concentrations were obviously different.The aluminum tolerance of XET enzyme in the roots of tea plants is much higher than that of Arabidopsis and other aluminum resistant plants.The root phenotype and root parameter of tea plants treated with aluminum addition not more than 1.0 mmol?L^-1 showed the phenomenon of promoting growth,especially that of 0.4 and 1.0 mmol?L^-1 aluminum treatment induced the root system expansion?elongation and division to promote root growth significantly.With the increase of aluminum concentration(>1.0 mmol?L^-1),this effect gradually weakened,indicating that aluminum promoting root growth of tea plants has physiological threshold.Aluminum below 1.0 mmol?L^-1could induce the up-regulation of CsXTH14?CsXTH23?CsEXPB14 and CsEXLA8 genes at some aluminum treatment time points and increased Expansins activity in the roots of tea plants.There were a positive correlation between root growth and the gene expression of XTHs and Expansins and their corresponding protein activity,which indicated that the treatment with certain concentration of aluminum(?1 mmol?L^-1)could induce the roots of Longjing43 CsXTH14 and CsXTH23 gene at 6h,24h,28d and 42d,the CsXTH14 and CsXTH23 of Baiye1at 6 h,7d and 28 d,the CsEXPB14 of Longjing 43 at 6 h and 7 d,and the CsEXPB14 of Baiye 1 at 6 h,24 h,7 d,28 d and 42 d,the CsEXLA8of Longjing43 at 6h,24h,7d and 28d,the CsEXLA8 of Baiye 1at24h,28dand42d,gene expression up-regulated,respectively;and increased Expansins activity in the roots of tea plants.It can promote the growth of tea root system by promoting the expansion,elongation and adventitious root formation of tea roots.The response of root system growth to aluminum in different tea varieties were different.The biomass increase of Baiye1 roots were significantly higher than Longjing 43,when the concentration of aluminum were less than 1.0 mmol?L^-1.Compared with the control without aluminum,the activitiy of XET,which were related to root growth,were significantly increased in Longjing 43 for 28 days and Baiye1 for 42 days treated with 0.4 mmol?L^-1 Al concentration,but were inhibited with 4.0 mmol?L^-11 Al treatment.2.The short-term effect of aluminum on the gene expression of XTHs and Expansins in tea root tips showed that the tea root tips,whether in vitro or not,were cultured under 0.4 mmol?L^-11 aluminum treatment,except that CsXTH14 gene expression were up-regulated at 18h time point and it were up-regulated at other time in vitro.The response of CsXTH14,CsXTH23,CsEXPB14 and to time gradient were continually up-regulated or continually up-regulated after a brief down-regulation,and when the culture time reached 21h,genes expression showed down-regulation.Especially,in vitro tea root tip,it showed obvious consistent change pattern.It indicated that the gene expression of XTHs and Expansins were very rapid in the short-term treatment of aluminum.This may play a key role in promoting root elongation and meristem growth of tea plants significantly.