Protonemal Morphogenesis of the Moss Tetraphis pellucida Hedw. in Culture and in the Wild

In axenic culture, the protonemal filaments of Tetraphis pellucidaderived from either spores and gemmae, or excised stems andleaves, share a mixture of attributes of chloronemata and caulonemata.Indirect immunofluorescence reveals that the tip cells containcortical and endoplasmic arrays of microtubules at interphase,and phragmoplasts associated with cell plate formation, butpre-prophase bands are absent. Protonemal plates originate fromthe same sites as filamentous protonemal side branches or directlyfrom young gemmae or excised stem fragments. These plates havea cylindrical base, the latter producing a single gametophorebud, and a unistratose lamina. The gametophores produce gemmacups in culture with the vegetative life cycle taking approximately28 d. Gibberellic acid (GA₃) has no visible effect on protonemal morphogenesiswhereas the auxin naphthalene acetic acid (NAA) suppresses plateand side branch formation. In the presence of kinetin the platesare callus-like and produce supernumerary buds. Abscisic acid(ABA) induces malformed plates and filaments with swollen cells,similar to those found in ageing cultures. Rhizoids are produced in abundance from gametophores and protonemalplates in nature but were never seen in culture. In the wild,rhizoids produce numerous protonemal plates and occasional gametophorebuds. The former are the main source of new shoots. The filamentousprotonemal phase in nature mainly comprises upright filamentscontaining one or more abscission cells. The protonemal plates in Tetraphis are homologous with thosein the allied genus Tetrodontium but are very different fromthose in Diphyscium and Sphagnum. Differences between cultureand nature are attributed to lower nutrient levels and irradiancesin the wild. Tetraphis pellucida, protonema, moss, morphogenesis, immunocytochemistry, gemmae, tip growth, vegetative reproduction