Study On Salt Tolerance Mechnism Of Tomato By Transformation Of Yhem1Gene

Tomato (Lycopersicon esculentum Mill.) is a juicy berries herb in Solanaceae family (Solanaceae), which is one of the main vegetables with the great economic benefits widely cultivated in open fields or protected facilities. However, in recent years, the continuous agricultural cultivation, unreasonable irrigation and facility application have aggravated the degree of soil secondary salinization, which is a seriously adverse factor for tomato growth and profit. Therefore, how to improve tomato salt tolerance is the key problem to solve the tomato industry.5-Aminolevulinic acid (ALA) has been suggested to be able to improve plant salt tolerance. In animal and yeast, ALA-S is a rate-limiting enzyme for ALA synthesis pathway. In Arabidopsis, GluTR is encoded by HemAl that is regulated by light. Recently, Zhang (2010) transformed YHeml gene, which was a divalent carrier comprised of Athaliana hemAl promoter (a light responsive promoter) and Saceharomyces cerevisiae Heml, encoding5-aminolevulinic acid (ALA) synthase in yeast into tomato, and the obtained transgenic plants was demonstrated possesssing greater photosynthetic capacity than the wild type, but it is yet unclear that YHeml gene transformation could enhance salt tolerance of tomato plants or not. In this work, the transgenic tomato was used as materials to explore the effects of200mmol·L-1NaCl stress on ALA metabolism, reactive oxygen metabolism, photosynthetic characteristics and related gene expression, the results obtained revealed that YHeml gene transformation could improve salt tolerance of tomato plants.1. After plants were treated by200mmol-L’1NaCl solution, the endogenous ALA levels, ALA synthetic, catabolic capacities, the relative expression of gene related with ALA synthase and ALA dehydratase and the chlorophyll content in leaves declined more in wild type (WT) than the transgenic plants. Moreover, salt stress increased the relative expression quantity of HemAl (coding GluTR gene in higher plant) and GSA (coding GSA-AM gene in higher plant) more in WT than that of transgenic plants, suggesting that YHeml transformation would depress C5route ALA biosynthesis in tomato plants.2. When tomato plants were treated by200mmol·L-1NaCl, the net photosynthetic rate, the fluorescence yield and the biomass were significantly decreased. However, the transgenic tomato remained higher leaf photosynthetic performance index (PIABS and PICS) and probability of a trapped exciton moves an electron into the electron transport chain beyond QA(Ψo)and electron transport(ETo/CS and ETo/RC)than the wild type. Meanwhile, the heat dissipation (DIo/CS and DIo/RC, amplitude of the K step (Wk) and approximate initial slope of the fluorescence transient (Mo) were lower in transgenic plants than that in the wild type. The transgenic plants also had higher relative expression quantity of the coding gene related with photosynthetic enzymes (RCA and Rubisco small subunit). This suggested that Yheml transformation might increase both light and dark reaction of photosynthesis in tomato leaves under salt stress.3. When tomato plants were treated by200mmol·L-1NaCl solution, the O2’production rate and malondialdehyde (MDA) content increased while the activities of superoxide dismutase (SOD),catalase (CAT),peroxidase (POD) and ascorbic peroxidase (APX) increased firstly and then decreased in both WT and transgenic plants, but higher enzyme activity was found in transgenic plants than that in the wild type. Meanwhile, most of the genes which encode the antioxidant enzymes were expressed more in the transgenic plants than that of WT. Therefore, transgenic plants possessed higher antioxidant capacity under salt stress than the wild type. Moreover, the H2O2content was generally higher in transgenic plants than in the WT, although it was kept at the high level in both genotypes under salt stress, which suggested that H2O2might be a molecular signal involved in cellular regulation.