Abstract: YHem1 was a Saceharomyces cerevisiae Hem1 gene，controlled by an Athaliana HemA1 promoter（a light responsive promoter）. When YHem1 was transformed into tomato plants，the leaf endogenous ALA content，the capacities for ALA biosynthesis and catabolism，the chlorophyll content and the antioxidant enzyme activities were all improved，while the superoxide anion（）production rate and the malondialdehyde（MDA）content were depressed significantly. Treatment by 200 mmol · L^-1 NaCl solution dramatically decreased the ALA biosynthetic and catabolic capacities，and the chlorophyll content in the wild type of tomato plants. It also induced increase of the production rate and the H₂O₂ and MDA content，but inhibited the activities of superoxide dismutase（SOD），catalase（CAT），peroxidase （POD）and ascorbic peroxidase（APX）. In the transgenic plants，the ALA metabolic capacities，the chlorophyll content and the antioxidant enzyme activities were also affected by salt stress，but the impacted seriousness was much lower than that in the wild type. Ten days after salt treatment，the transgenic plants kept higher biomass with less salt-induced inhibition，compared with the wild type，which suggested that the YHem1 transformation into tomato might improve its salt tolerance. Additionally，the H₂O₂ content was generally  higher in transgenic plants than in the WT，either under salt stress or not，which implied that H₂O₂ might be a molecular signal involved in cellular regulation.

Key words: tomato, 5-aminolevulinic acid（ALA), antioxidant enzyme, salt tolerance, YHem1