Introduction of Yeast Metallothionein Gene (CUP1) into Plant and Evaluation of Heavy Metal Tolerance of Transgenic Plant at the Callus Stage

For phytoremediation, it is necessary to use plants with a large biomass and ability to absorb and accumulate heavy metals. Attempts were made to produce heavy metal-tolerant plants by introducing a metallothionein gene, CUP 1, into plants with a large biomass. In the present study, we evaluated the heavy metal tolerance of sunflower plants at the callus stage in terms of 2,3,5-triphenyl-tetrazolium chloride (TTC)-reducing activity, measured the mRNA expression level of the introduced gene, and selected tolerant clones. The transgenic calli of several strains showed a high TTC-reducing activity even after treatment with Cd 200 μM for 10 d. In the transgenic calli of a few strains, which showed a low TTC-reducing activity, the amount of metallothionein was lower than that in the other transgenic strains. Conversely, some transgenic calli with a high TTC-reducing activity expressed a much higher amount of mRNA of the introduced gene.