Lead and cadmium tolerance and accumulation of proanthocyanidin-deficient mutants of the fern Athyrium yokoscense

The fern Athyrium yokoscense often flourishes around mine sites in Japan and can tolerate and accumulate heavy metals such as lead (Pb) and cadmium (Cd). In this work, we examined whether proanthocyanidins, also called condensed tannins, were involved in the mechanisms of Pb and Cd tolerance and accumulation of A. yokoscense because proanthocyanidins are known to alleviate metal stress in several plant species and are present at high levels in A. yokoscense. For this purpose, we used mutant gametophytes deficient in proanthocyanidins, in which the relative proanthocyanidin contents were 20% of those of the wild-type gametophytes. Although the proanthocyanidin contents of the mutant were quite low, the growth of the mutant was very similar to that of the wild-type gametophytes even in the presence of 80 mg/kg Pb or 48 mg/kg Cd. Under the same conditions, the mutant gametophytes also accumulated Pb and Cd as much as the wild-type gametophytes did. These results indicate that the proanthocyanidins in A. yokoscense are not important for the Pb and Cd tolerance and accumulation properties.