CONSEQUENCES OF ULTRAVIOLET RADIATION ON THE DIFFERENTIATION AND GROWTH OF FERN GAMETOPHYTES

Summary The effects of ultraviolet light (u.v.), principally at 2537 Å, on the differentiation and growth of gametophytes in Pteris vittata, Osmunda japonica and Dryopteris varia were investigated. It was ascertained that a single cell may be isolated by u.v.‐irradiation and that a normal gametophyte can be regenerated from such a cell. When gametophytes grown under low intensity (150 lux) white light before u.v.‐irradiation were irradiated with a high dose, an apico‐basal gradient of ability to survive was clearly shown. The survival of each of the cells composing a protonema seems to be related to two different factors; a marked ability for cell division or rapid recovery from the damage of u.v. at the apical region and a high resistance to u.v. at the basal region. Under both culture conditions, cells of a definite length alone survive. General effects induced by the u.v.‐irradiation include reversal of the polarity in a protonema and modification of the developmental axis. In addition, swelling of the rhizoid and protonema cells, and occurrence of ‘rhizoidal protonema’ were also described.