Plant Growth Regulatory Activity of Secondary Metabolites Produced by the Invasive Xanthium spinosum’s Endophytic Dematiopleospora sp.

Alien invasive species harbor specific endophytes that are not only rich resources of eco-friendly bioactive secondary metabolites but also might help explain their invasion success. In this study, 5 mycotoxins, i.e., tyrosol (1), sterigmatocystin (2), 1-hydroxy-3-methylxanthone (3), carpesterol (4), and mellein (5), were isolated from the endophytic fungus Dematiopleospora sp. of the invasive plant Xanthium spinosum. In general, all isolated compounds exhibited significant promotive activity on 4 receiver species in a dose-dependent manner when applied concentrations ranged between 5 ~ 100 µg/mL, whereas suppressive effect occurred when applied concentration reached 500 µg/mL. Among the tested species, Medicago sativa was the most sensitive plant, whose root length was twofold of the control when treated by 5 at 5 µg/mL, and promoted by 93.20% by 4 at 5 µg/mL, indicating that 5 possessed the most potent stimulatory activity; 1 and 2 showed similar moderate activity, whereas 3 and 4 exhibited equivalent potent activity. Further study revealed that 2 affected the phytohormone levels as well as the anti-oxidant system of M. sativa seedlings, including reducing the content of IAA, ABA, and MDA but increasing the content of CTK and the activities of SOD, POD, and CAT. Our work is the first report on the growth regulatory activity of 3 and 4, as well as elucidation on the mechanism of 2.