The mechanism of seed coat-imposed dormancy revealed by oxygen uptake in Chatham Island forget-me-not Myosotidium hortensia (Decne.) Baill

Chatham Island forget-me-not Myosotidium hortensia (Boraginaceae) is a monotypic genus endemic to the Chatham Islands of New Zealand. Myosotidium hortensia is threatened in its natural environment by introduced grazing animals and weeds. Further to this, the conservation and reintroduction efforts of M. hortensia are hindered by their dormant seeds. The dormancy is imposed by the seed coat but the underlying dormancy mechanisms are not well understood. Understanding the dormancy mechanisms in this species will help in revegetation efforts. This work aims to elucidate mechanisms by which the seed coat imposes dormancy in M. hortensia by determining the germination after manipulation of the seed coat and measuring changes in oxygen uptake in response to this manipulation. The structure of the seed coat was assessed using scanning electron microscopy and the presence or absence of lignin in the seed coat determined. As with other Boraginaceae, the seed coat of M. hortensia does not restrict water penetration into the seed. Oxygen uptake was 4.5 fold higher in decoated than in intact seed. There was no significant increase in oxygen uptake for the seeds when their seed coat had been pierced or pierced and resealed with vaseline. However, the germination rate, as measured by radicle emergence, was faster in these seeds. These findings, in addition to the structural analysis of the seed coat which revealed that the seeds have secondary thickening but no lignin, confirmed that mechanical constraint of embryo growth was preventing germination.