Promotive effect of 5-aminolevulinic acid on the antioxidant system in Ginkgo biloba leaves

The effect of 5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins, at low levels (10 and 100 mg l-1) on the antioxidant system in Ginkgo biloba leaves were investigated. The results showed that ALA-treatment accelerated hydrogen peroxide accumulation and temporarily increased the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) at day 4 and 8. The activities of glutathione reductase (GR) and dehydroascorbate reductase (DHAR) and the contents of ascorbic acid (AsA) and glutathione (GSH) were all significantly increased by ALA, while dehydroascorbate (DHA) content was decreased and no variety was observed in oxidized glutathione (GSSG) content after ALA treatment. The ALA-treated leaves had higher values of AsA/DHA and GSH/GSSG than those in the control leaves. These results suggested that foliar treatment with a low concentration of ALA might provide a useful means of improving beneficial antioxidant activity in G. biloba leaves.