A Study On The Uptake,Accumulation And Tolerance Of Copper In Apple Rootstocks

Atmospheric emissions,sewage irrigation and excessive application of pesticide and chemical fertilizers induces Cu pollution in orchard more and more serious,which limits apple production sustainability.Copper,an essential micronutrient for plants growth,plays a pivotal role in plants physiological metabolism,however,it is also toxic to plants in high levels.Rootstocks can regulate growth and development of fruit tree and increase the tolerance capability of fruit tree to environment stress.The concentration of Cu in scion is directly affected by the uptake and transport capacity of Cu in rootstocks.Variation of Cu uptake,transport and accumulation existed among plant species or even among cultivars and genotype within species,which provide possibility for screening Cu tolerance apple rootstocks with low Cu accumulation.In the present study,Malus asiatica Nakai.,M.baccata Borkh.,M.hupehensis Rehd.,M.micromalus Makino.,M.prunifolia Borkh.and M.prunifolia Borkh.‘guodongxian‘were used as materials to explore the differences of Cu translocation and tolerance among different apple rootstocks at the physiological and molecular level.The knowledge gained from the present study will provide a scientific basis for screening apple rootstocks with low Cu accumulation and high tolerance.The main results were as follow:These six apple rootstocks exposed to 5?M or 20?M Cu showed high tolerance to Cu stress,and the variation of Cu tolerance existed among them.Lower Cu dose?5?M?imposes less significant toxic effects on all apple rootstocks.However,higher Cu?20?M?lever significantly declined plant biomass,chlorophyll,root configuration parameter and nutrients uptake in most of these apple rootstocks.This decline was more prominent in M.hupehensis and M.prunifolia‘guodongxian‘performed better as compared to other apple rootstocks.In comparison with the other five apple rootstocks,M.prunifolia‘guodongxian‘displayed the highest Cu concentrations,total Cu and BCF in roots,but lowest T_f.however,M.hupehensis is to the opposite.The root system of six apple rootstocks exudates phenolic compounds?catechin,coumaric acid and cinnamic acid?and organic acids?malic acid,oxalic acid,citric acid and succinic acid?,but their contents were different.In addition,in apple rootstocks,it was foud that to immobiliza Cu in cell wall and vacuole and to convert it into pectates-or protein-integrated forms,undissolved Cu phosphate forms or oxalate forms may be the primary strategies to reduce Cu mobility and toxicity.Cu-induced led to greater ROS and MDA accumulation,carbohydrates and antioxidants were in line with the variations of Cu tolerance among six apple rootstocks.In comparison with the other five apple rootstocks,M.prunifolia‘guodongxian‘has lower concentrations of H₂O₂ and MDA in roots,stems and leaves,but higher concentrations of carbohydrate and enhanced antioxidants under 20?M Cu stress.However,M.hupehensis is to the opposite.In comparison with the other five apple rootstocks,The lower transcript levels of genes involved in Cu uptake and transport,sucn as COPT1,COPT2,HMA5 and HMA7,whereas stronger mRNA levels of MT2,YSL2,Cu/Zn-SOD NRAMP3 and HMA2,associated with Cu detoxification were found in M.prunifolia‘guodongxian‘under 20?M Cu stress.However,M.hupehensis is to the opposite.Under the current experiment conditions,M.prunifolia‘guodongxian‘are more tolerant to Cu stress than the other five apple rootstocks,however,M.hupehensis are the most sensitive apple rootstocks.