EFFECTS OF DARK OR OF RED, BLUE OR WHITE LIGHT ON GERMINATION OF SUBTERRANEAN CLOVER SEEDS

Abstract

Dry or imbibed seeds of the negatively photoblastic burr burying subterranean clover cv. ‘Seaton Park’ were treated with dark or with
red, blue or white light to evaluate the effects of light on seed germination. Dry seeds treated with constant white light, red light or blue
light during 8 days and subsequently incubated in dark had final germination and duration of germination reduced, and the distribution of
germination changed from highly asymmetric to symmetric respectively. Imbibing seeds incubated under constant blue or white light had
final germination strongly reduced seven days after sowing (7.3% and 50.1% of the germination under dark) with significant differences
between them. After transferral to dark, true complete recovery of germination of seeds treated with white light was observed 19 days
after sowing, but only partial recovery in seeds treated with blue light. Results of dry and imbibed seeds are consistent with no activity of
phytochromes, as expected in negatively photoblastic seeds. Results of dry seeds are seemingly contradictory because total germination
data imply the inactivity of red and blue light photoreceptors, the opposite being implied by duration and shape of germination. A tentative
hypothetical solution for the contradiction is presented. Results of imbibed seeds are fully consistent with cryptochromes but not with
phototropins mediation of responses to light of seed germination in ‘Seaton Park’. The ecological and adaptive significance of such
responses are discussed in the framework of light attenuation in soil and the requirement and ability of subterranean clover ‘Seaton Park’
to bury seeds.