In the past, the activity of the promoter of a metallothionein gene expressed in actinorhizal nodules of Casuarina glauca, CgMT1, has been analysed in Casaurinaceae and in tobacco, Arabidopsis and rice. In all these plants, the promoter showed high activity in the root cortex and –epidermis, making it a useful tool for the expression of transgenes. Therefore, its activity was now analysed in transgenic root systems of Datisca glomerata, an actinorhizal plant from a different phylogenetic group than C. glauca, using the same CgMT1::GUS fusion as in previous studies. However, in contrast with all other plant species examined previously, the CgMT1::GUS construct showed no activity at all in D. glomerata hairy roots, while the expression pattern in nodules resembled that found in C. glauca nodules. This is probably due to the changed hormone balance in hairy roots since experiments on the CgMT1::GUS construct in transgenic Arabidopsis showed that CgMT1 promoter activity was repressed by auxin or cytokinin, respectively. Yet, in hairy roots of the model legume Lotus japonicus induced by the same Agrobacterium rhizogenes strain, the CgMT1 promoter was active in roots and not in nodules, indicating that while pRi T-DNA genes lead to a changed hormone balance, the changes do not abolish the differences in phytorhomone levels/-sensitivity between plant species.