| Drought is one of the most serious abiotic stresses suffered by plants.However,plant grafting plays an important role in enhancing the process of adapting to adversity stress by changing the material and information exchange of plant roots and shoots.For this reason,this study used drought-tolerant tomato '606'(T)and drought-sensitive tomato '112'(S)as test materials to study the growth status,nutrient absorption,light energy utilization,active oxygen balance and other physiological metabolic of seedlings grafted with each other under drought stress.Then through transcriptome analysis,the drought-tolerant genes were screened in order to clarify the mechanism of the interaction between rootstock and scion that affects the drought tolerance of grafted tomato seedlings.The main findings are as follows:1.There are significant differences in the growth,water use efficiency,and photosynthetic rate of tomato grafted seedlings with different rootstock and scion under drought stress.The WUE,Pn,Fv/Fm and ?PSII of tomato grafted seedlings with drought-tolerant rootstocks were significantly higher than those of drought-sensitive rootstocks grafted seedlings.For example,the Pn of S/T increased by 10.97% compared with S/S at 5 d of drought stress.When drought stress was treated for 15 d,the dry weight,root length,root surface area and plant growth rate of grafted tomatoes on drought-tolerant rootstock were significantly higher than those of grafted tomato seedlings on water-sensitive rootstock.For example,the growth rate of S/T in 15 d of drought treatment was 21.05%higher than that of S/S.2.Under drought stress,the content of mineral elements,carbohydrates(sucrose,fructose,glucose,total carbohydrates)and organic acids(oxalic acid,succinic acid,citric acid,malic acid,tartaric acid,proline)and other osmotic adjustment substances in tomato seedlings grafted with drought-tolerant rootstocks were significantly higher than those grafted with drought-sensitive rootstocks.For example,compared with S/S,the contents of K and Mg in the leaves of S/T treatment increased by 10.64% and 11.14%,respectively,and the total carbohydrate and proline of leaves increased by 53.12% and 20.83,respectively.Not only that,the grafted tomato seedlings with drought-tolerant rootstocks had strong root vigor under drought conditions,and the leaves had large stomata openings,which was conducive to maintaining high water potential and water-air exchange on the leaves.For example,root vigor in T/T and S/T treatments was increased by 12.15% and 10.28% compared with S/S treatment,respectively.3.Drought stress significantly increased the accumulation of H2O2,O2·-and MDA in leaves and roots of tomato plants,but the ROS level and MDA content of grafted seedlings with drought-tolerant rootstocks were significantly lower than those of grafted seedlings with drought-sensitive rootstocks.For example,when drought stress was treated for 15 days,the MDA content in the leaves of T/T and S/T treatments was 42.21% and 31.37% lower than that of S/S treatment,respectively.Under drought stress,the activities of key enzymes such as SOD,POD,CAT,APX,AAO,GR,etc.and the content of antioxidants such as ASA,DHA,GSH,GSSG,etc.of the antioxidant system of tomato leaves and roots for each treatment increased significantly.And the antioxidant enzyme activity of grafted tomato seedlings with drought-tolerant rootstocks increased greatly,and the ratio of ASA/DHA and GSH/GSSG was increased.For example,when drought stress was treated for 15 days,the SOD activity and ASA/DHA ratio in leaves of S/T treatment were increased by 76.36% and 7.74% respectively compared with S/S treatment.It showed that grafted tomato seedlings of drought-tolerant rootstocks were beneficial to reduce the accumulation of ROS caused by drought stress,thereby reducing the oxidative damage caused by drought.4.Through transcriptome sequencing of the leaves and roots of S/T and S/S grafted tomato seedlings treated with drought stress for 10 d,a total of 509 differentially expressed genes were screened from the leaves and 3946 differentially expressed genes were screened from the roots.KEGG pathway analysis showed that the differential genes in the leaves of different grafted seedlings were mainly enriched in flavonoid biosynthesis,ascorbic acid and alditol metabolism,plant circadian rhythm,phenylalanine metabolism and phenylpropane biosynthesis pathways;differential genes in roots mainly enriched in galactose metabolism,starch and sucrose metabolism,ribosomal biogenesis in eukaryotes,glycolysis/gluconeogenesis,and phenylpropane biosynthesis pathways.5.We further analyzed the transcriptome data to screen the key differential genes for drought tolerance.Compared with S/S grafted seedlings,S/T grafted seedlings have more genes related to plant hormone signal transduction in roots than leaves,and most genes are up-regulated in S/T.Especially the differential genes involved in ABA biosynthesis and ABA signal transduction had changed significantly,but compared with ABA biosynthesis,there are more differential genes related to ABA signal transduction.6.According to the transcriptome data,the related differential genes GOLS1 and NIP2;1of the galactose metabolism pathway and the aquaporin family were selected for gene cloning and functional verification.The coding sequence of GOLS1 is 957 bp,which encodes 318 amino acids,and the coding sequence of NIP2;1 is 852 bp,which encodes 283 amino acids.GOLS1 and NIP2;1 in tomato plants are similar to homologous genes in potato.Drought stress induced the expression of GOLS1 and NIP2;1,the higher the expression level,the stronger the drought tolerance of grafted tomato seedlings. |
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