Effects Of Drought Stress On Water Physiology And AQPs Expression In Two Apple Rootstocks

Based on the bioinformatics method,the phylogenesis,gene structure,amino acid physicochemical properties and the conserved motifs of apple aquaporin gene family(AQPs)were analyzed.AQPs of apple were comprehensively understood.Malus baccata Borkh.and M26(Malus pumila Mill.)were used as materials.The mild drought stress(D1;60-65% of field water holding capacity),moderate drought stress(D2;45-50% of field water holding capacity),severe drought stress(D3;25-35% of field water holding capacity)and control(CK;70-80% of field water holding capacity)were set up.The changes of water physiology were measured to understand the effect of drought stress on water physiology of M.Baccata and M26,and the rehydration was carried out after drought stress in order to detect the drought recovery for three days.On the basis of the above experiments,the relative expression levels of AQPs in apple under drought stresses were determined by fluorescence quantitative analysis.The main conclusions are as follows:1.Apple aquaporin genes family has a certain family characteristics.Thirty AQPs of apple can be divided into three subfamilies.Gene structure of AQPs contains2 to 7 exons,which were located on 15 chromosomes of apple,while there w no AQPs on chromosome 2 and 4.Amino acid sequence of AQPs containing NPA characteristic sequences and conserved motifs(TGINPARSI/FGAAI/VI,SGXHXNPAVT and GGGANXXXXGY).Similar to other plant AQPs,apple AQPs presents a certain family characteristics and conservation.2.Drought stress could significantly affect the changes of water physiology of M.baccata and M26.When the stress was severe,the leaf water potential,leaf water content,free water content,root water content and stem water content in M.baccata was decreased by 66.3%,32.16%,59.13%,30.47% and 20.73%,respectively.Simultaneously,the leaf water potential,leaf water content,free water content,root and stem water content in M26 was decreased by 60.72%,27.51%,50.30%,42.50%and 38.06%,respectively.After drought stress was relieved,rehydration could gradually restore water physiology.The water content of matrix was positively correlated with leaf water potential,tissue water content,root and stem water content.3.There was a significant difference in the expression levels of apple AQPs in the leaves and roots of the M.baccata and M26.This difference was mainly manifested in two aspects.First,there were significant differences in the expression ofthe same gene in the leaves and roots of the two varieties.The relative expression levels of Md NIP1;2,Md NIP4;2,Md NIP4;1,Md NIP5;1,Md NIP6;1,Md?-TIP and Md?-TIP were higher in the leaves of M.Baccata,while Md TIP1;3,Md TIP2;2,Md?-TIP and Md?-TIP were higher in its roots.In addition,the relative expression levels of Md PIP1;4,Md PIP2;4,Md NIP1;2,Md NIP4;1 and Md NIP5;1 were higher in leaves of M26,whereas Md TIP2;2,Md TIP1;3,Md TIP5;1,Md?-TIP,Md?-TIP,Md NIP5;1,Md NIP6;1 and Md NIP4;1 were higher in its roots.Second,the specific expression of individual APQs in leaf or root.Md PP1;4 was expressed only in the roots of M.baccata,but not in its leaves.Md TIP1;3 and Md TIP2;2 were expressed in the leaves of M26 with mild or moderate stress.Simultaneously,drought stress could significantly affect the expression levels of AQPs in apple.