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Melanin produced by a dark septate endophyte, Exophiala pisciphila, was isolated and purified. The solubility properties, Ultraviolet-visible and Fourier transform infrared spectra of the purified E. pisciphila melanin were similar to those of typical melanin. Inhibition of melanin production was observed when colonies exposed to tricyclazole (1,8-dihydroxynaphthalene (DHN) melanin inhibitor), but not to kojic acid (3,4-dihydroxyphenylalanine melanin inhibitor). Thus the E. pisciphila melanin was a member of DHN melanin family. In addition, the antioxidant activities of E. pisciphila melanin were evaluated in vitro by 1,1-diphenyl-2-picryl-hydrazyl radical-scavenging assay. E. pisciphila melanin exhibited a strong antioxidant activity. Addition of 50-350 mg L -1 Cd(II) to the medium increased the melanin production in E. pisciphila.

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Dark septate endophytes (DSE) are widely distributed in plant roots grown in stressful habitats, especially in heavy metal-polluted soils. But little is known about the physiological interactions between DSE and plants under heavy metal stress. In the present study, the growth, Cd content, and physiological response of Zea mays L. to a root-colonized DSE, Exophiala pisciphila, were analyzed under Cd stress (0, 5, 10, 20, and 40 mg/kg) in a sand culture experiment. Under high Cd (10, 20, and 40 mg/kg) stress, the DSE colonization in roots increased the maize growth, kept more Cd in roots, and decreased Cd content in shoots. The DSE colonization improved the photosynthesis and induced notable changes on phytohormones but had no significant effect on the antioxidant capability in the maize leaves. Moreover, there were significant positive correlations between the gibberellic acid (GA) content and transpiration rate, zeatin riboside (ZR) content, and photosynthetic rate in maize leaves. These results indicated that the DSE's ability to promote plant growth was related to a decrease on Cd content and the regulation on phytohormone balance and photosynthetic activities in maize leaves.

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