| Cadmium(Cd)is a major pollutant of heavy metals in soil and it is also one of the major heavy metal pollutants in vegetables.Cadmium can easily stay in vegetables,other foods,the human body and other organisms through the food chain,causing harm to animals and plants and the ecological environment.Tomato(Lycopersicon esculentum Mill.)is an annual or perennial herb assigned to family Solanaceae,and is also one of the important crops in China.Lycopersicon esculentum showed different performances after toxicity treatment by heavy metals: leaf necrosis,new leaves chlorosis,and purple-red on the back of leaf petioles and leaves.2,4-Exogenous epibrassinolide(2,4-EBL),as the sixth largest plant hormone,plays an important role in plant growth and development.Nowadays there are many studies on plant growth and development of 2,4-EBL,but few reports on the effects of 2,4-EBL on tomato seedlings under heavy metal Cd stress.Therefore,conventional cultivars of tomato are chosen as the experimental material.In the present study,tomato seedlings after spraying Cd stress with 2,4-EBL and soaking with 2,4-EBL were carried out.The work aimed at investigating the morphological characteristics,growth status,physiological responses of tomato under stress of 2,4-EBL and the expression levels of 2,4-EBL signal transduction genes,metal transporter genes and enzyme activity-related genes.It is found that 2,4-EBL regulate the physiological mechanism of tomato responses to Cd stress.The results show that:(1)Growth status: the length of the main roots of tomato plants treated with 2,4-EBL after Cd stress was significantly increased,and the plant height was significantly higher than that of the single Cd control group.Seedlings soaked with tomato seedlings were treated with Cd and compared with the single Cd treatment group.After soaking treatment,Cd solution(Td)was poured and the plant height,root length,and fresh weight increased to varying degrees.Compared with spray treatment,plant height,root length,fresh weight,and dry weight after soaking treatment were higher in the treatment group with spray treatment 2,4-EBL than those during the same growth time.(2)Physiological response: In this work,the activity of 4 antioxidant enzymes(SOD,POD,APX,and GR)of tomato seedling leaves and roots under 2,4-EBL treatment with Cd stress was investigated,showing that the antioxidant enzyme activities of 2,4-EBL+Cd treatment group increased to varying degrees;the proline and MDA contents of tomato after Cd stress treatment with 2,4-EBL decreased compared to those of single Cd control group,and the leaves and roots decreased.They are all significantly different from the third day.Antioxidant enzyme activity of Cd(Td group)solution after soaking in leaves and roots of tomato seedlings was slightly higher than that of single water control group(Ta group),but it was significantly lower than that of single Cd treatment group.It showed that the increase of active oxygen by Cd stress after soaking was not significant,and no excessive peroxidase was used by plant to remove active oxygen.Oxidative damages of plants,the changes of antioxidant enzyme activity,fluctuations of proline and MDA content indicated that the damage degree of plants under heavy metal Cd stress reduced.(3)Gene expression: Compared with 2,4-EBL+Cd group,BAK1 gene,BRI1 gene and BES1 gene were increased at 3h,6h,and 12 h respectively in a single Cd treatment group,and APX1 gene expression levels in leaves from 6h.The expression of APX1 gene in the root(3h~12h)was also higher than that in the single Cd treatment group.The expression of IRT1 gene in tomato leaves ascended when spraying tomato seedlings treated with 2,4-EBL and Cd stress after soaking treatment,while in roots descended only with the soaking treatment.(4)Cloning and bioinformatics analysis of the full-length coding region of tomato BAK1 gene: In this work,Lycopersicon esculentum was used as material,and the full-length cDNA sequence of a brassinosteroid signal transduction gene was obtained by homologous cloning.The sequencing result showed 99% homology with the reference sequence in GenBank.The gene sequence was 1671 bp in length and encodes 218 amino acids.The results showed that the secondary structure of the protein was mainly composed of 42.20% ?-helix,11.01% ?-sheet and 28.44% random coil,and there was also a small amount of extended chain(18.35%).Tomato and fluffy tobacco,tobacco,potato,Polina,tomato mutual support,the support rate was only 50%.(5)Cloning and bioinformatics analysis of the full-length sequence of the coding region of tomato BES1 gene: tomato gene was cloned by homologous cloning method,and the full-length cDNA sequence of BES1,an EBL signal transduction gene,was cloned and sequenced.The length was 1218 bp which encoding 325 amino acids.Secondary structure prediction of tomato BES1 protein showed that the secondary structure of the protein was mainly composed of 18.15% alpha helices,8.92% beta-sheets,and 60.62% random coils with a small amount of extended chains(12.31%).In addition,It is found that Tomato and Plinin tomato had a high homology with potato. |
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