Overexpression of the Tamarix hispida ThMT3 gene increases copper tolerance and adventitious root induction in Salix matsudana Koidz.

In this work, transgenic Salix matsudana expressing the Tamarix hispida ThMT3 gene, which encodes encoding a type 3 metallothionein, showed increased tolerance to copper (Cu) stress. Exposure to 50 mu MCu completely inhibited rooting of wild-type (WT) plants, but induced numerous adventitious roots in the transgenic plants. The nitric oxide (NO) content in the transgenic plants was higher than that in WT plants. The application of an NO inhibitor, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, decreased superoxide dismutase, catalase and ascorbate peroxidase activities under Cu stress. Auxin application-related genes that are known to improve adventitious roots, such as Auxin response factor 8, auxin resistant1 and pinformed, were highly expressed in transgenic plants under Cu and sodium nitroprusside treatments. These results suggested that the expression of the ThMT3 gene increased Cu tolerance and NO production, and the higher NO release contributed to the induction of adventitious roots under Cu stress.