| Apple(Malus × domestica Borkh)is one of the main cultivated fruit tree species in China,its area and yield rank first in the world.However,some apple producing areas frequently encounters drought and salt stress,which seriously affects the yield and quality of apples and limits the development of apple industry.The resistance of apple rootstocks mainly depends on the rootstocks.Therefore,understanding the adaptive mechanism of apple rootstocks to drought and salt stress and tapping related genes are of great significance to improve the drought resistance and salt tolerance of apple.In this study,we investigated the role of ABA in regulating drought and salt tolerance of apple rootstocks(M.hupenensis Rehd.and M.toringoides Hughes)using physiology,biochemistry and transcriptome analysis.The aim is to provide a theoretical basis for the biological function and stress resistance improvement of apple.The main results are as follows:1.The growth of two apple rootstocks was inhibited under drought stress.Continued stress caused the leaves wilted and even the whole plant died.The two apple rootstocks withered on the 8th and 9th day of drought treatment respectively,and died on the 11th day.Net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)were also affected to varying degrees.Under drought stress,Pn,Gs and Tr of two apple rootstocks decreased by 63.34%-93.54%,41.80%-86.74%and 59.04%-83.22%compared with the control.However,drought stress had no significant effect on leaf conductivity and relative water content.Drought stress significantly increased the content of endogenous ABA in apple rootstocks.The content of endogenous ABA in two apple rootstocks under drought stress was 6.03%～44.92%higher than that of the control.Exogenous ABA could alleviate the adverse effects of drought on apple seedlings,mainly by increasing Pn and Gs.Compared with the drought treatment,Pn of M hupenensis Rehd was increased 35.57%～155.69%by exogenous application of ABA,Gs and ABA of M.toringoides Hughes was increased 37.79%～115.21%and 60.71%～98.19%respectively.2.Salt stress inhibited the growth of apple rootstock seedlings and decreased Pn,Gs and Tr.At the same time,the electrical conductivity of leaves and leaf relative water content were increased,and the content of endogenous ABA in plants was significantly increased.Under salt stress,the plant growth of M.hupenensis Rehd.seedlings decreased by 68.70%compared with the control.Under salt stress,the Pn,Gs and Tr of two apple rootstocks decreased by 36.16%～75.76%,13.91%～73.83%and 43.68%～67.73%respectively.The electrical conductivity and leaf relative water content increased by 13.53%～110.79%,8.99%～10.78%,and ABA content of M.toringoides Hughes was more than 81.77%.Under salt stress,the Pn,Gs and Tr of exogenous ABA treatment increased by 25.69%～69.09%,30.77%～74.74%and 17.26%～70.37%respectively,and the conductivity decreased by 23.24%～60.36%,while the content of endogenous ABA increased by 39.47%～135.45%.The results showed that ABA could alleviated the inhibition of salt stress on the growth of apple rootstocks,increased Pn,Gs and Tr,and improve the salt tolerance of apple rootstocks.3.Under drought and salt stress,the number of clean bases obtained from M.hupenensis Rehd.samples was 166.35 Gb,the clean data of each sample was above 6.63 Gb,and the percentage of Q30 base was not less than 94.08%.GO enrichment analysis of differentially expressed genes revealed that many genes were up-regulated or down-regulated in metabolic process,cellular process and catalytic activity.The number of differentially expressed genes involved in ABA under drought and salt stress was 55 and 15,respectively.KEGG metabolic pathway analysis of differentially expressed genes showed that these genes were up-regulated or down-regulated.Significant enrichment processes include:Biosynthesis of amino acids,nitrogen metabolism,arginine and proline metabolism,flavonoid biosynthesis phenylalanine,tyrosine and tryptophan biosynthesis,plant hormone signal transduction,starch and sucrose metabolism. |
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