Photomorphogenic and Chlorophyll Studies in the Bryophyte Marchantia polymorpha

The action of daily far-red (FR)-irradiations at the end of photoperiods of white fluorescent light was studied on orientation and chlorophyll content of green thalli of Marchantia polymorpha L. By the end of the night following the first FR-exposure, the chlorophyll content of the tips was already significantly lower than that of the controls, and there was a beginning of upward growth; by the end of the next 8-hour photoperiod and still before the second FR-irradiation, both the change in orientation and the pigment drop had become much more pronounced. After one week, a terminal 5 min FR treatment had resulted in 20 to 30% less chlorophyll for the tips after 8-hour days, and in ±10% less after 16-hour days; the morphogenic effects were also stronger after 8-hour than after 16-hour days. After three weeks under 8-hour photoperiods, the tips of the FR-treated thalli contained ±? less chlorophyll than the tips of the controls; for the basal parts of the thalli the drop was smaller. However, after 1-hour photoperiods, FR depressed the level of the basal parts much more than that of the tips: after one week 1 min FR caused a diminution of 20 to 30 per cent; a daily irradiation of 5 min caused a drastic bleaching, with 60 to 70 per cent less chlorophyll α than in the controls. The various FR-effects were always fully reversed by 2½ min R light. The results are interpreted in terms of the R, FR phytochrome-mediated system. The FR-induced change in orientation is thought to be linked to active growth. The FR-induced chlorophyll decrease can be explained by an effect on the regeneration of protochlorophyll as proposed for etiolated seedlings by several authors, but some of our data indicate the possibility of a greater chlorophyll catabolism in FR-treated than in control thalli.