Ribosomal RNA gene variation in diploid and tetraploid Tolmiea menziesii

Abstract

Evidence from gross morphology, karyology and flavonoid chemistry suggests that Tolmiea menziesii is one of the clearest examples of autopolyploidy in natural populations. To provide additional data regarding the origin of the tetraploid cytotype of Tolmiea, both the 5S and 18S-25S ribosomal RNA genes were studied at the restriction enzyme level. Using restriction enzymes that cut once per repeat, the lengths of the 5S and 18S-25S ribosomal genes were estimated in diploids and tetraploid plants. There appear to be no consistent differences between diploids and tetraploids for the repeat length of the 18S-25S ribosomal genes. Furthermore, there is no significant repeat length heterogeneity within tetraploid plants for these genes. In addition, no differences in repeat length of the 5S genes were observed among the diploid and tetraploid plants analysed. The homogeneity observed among diploid and tetraploid plants for repeat length of the 5S and 18S-25S ribosomal genes is consistent with the hypothesis that the tetraploid cytotype is of autopolyploid origin.