Morphogenetic role of kinetin and abscisic acid in the moss Physcomitrium

In the presence of kinetin, a supposedly gametophytic bud inducing substance, the secondary protonema of the moss Physcomitrium pyriforme Brid., as well as producing leafy gametophytes, continued to exhibit its normal tendency of forming sporophytic buds (i.e. buds with apical cells having two cutting faces). Also remarkable was that callus derived from the secondary protonema, when cultured in a kinetin supplemented liquid medium, formed exclusively apogamous sporophytic buds with a virtual exclusion of gametophytes. In the presence of abscisic acid, the elongation of protonemal cells as well as their differentiation was markedly suppressed. This effect was manifest even when abscisic acid was used in conjunction with kinetin. It is suggested that rather than having a morphoregulatory role, kinetin may be responsible merely for enhancing cell proliferation. The determination of an apical cell with two cutting faces (sporophytic) or one with three cutting faces (gametophytic) is under the control of other factors both external, (e.g. sucrose) and internal. It is proposed that abscisic acid can suppress the usual differentiational capacity of the moss tissue, even in a favourable environment.