Comparative development of the sporophyte–gametophyte junction in six moss species

Abstract

Developmental anatomy of the sporophyte-gametophyte junction in six moss species is described with special reference to sporophyte penetration into the gametophytic tissue. The sporophyte-gametophyte junction in mosses is classified into two types based on vaginula morphology: in the "true vaginula" type, the junction involves only an epigonium derived from the archegonium, and in the other "shoot vaginula" type, it involves a shoot and an epigonium. In both of the types, the sporophyte penetrates into an epigonial tissue accompanied by degeneration of epigonium cells under the developing sporophyte. In the "shoot vaginula" type, the sporophyte further penetrates into the conducting strand or similar cells that seem to be induced by stimulation of fertilization. It is likely that the difference in growth rate between the epigonium and the capped sporophyte is a mechanical force for sporophyte penetration.

A Physcomitrella PIN protein acts in spermatogenesis and sporophyte retention

“…The haustorium cells of the sporophyte foot are not pressed against the vaginula tissue but surrounded by a placenta-like space, while both tissues are separated by a diffusion barrier (Uzawa & Higuchi, 2010; Regmi et al ., 2017). The foot of the sporophyte is wider than the seta with a small depression between seta and foot, while vital sporophytes are tightly attached to the gametophore.…”

Filial mistletoes: the functional morphology of moss sporophytes

“…1A). Mitotic divisions of this meristem promote elongation of the embryonic axis and thereby facilitate penetration of the foot into gametophytic tissues (Vaizey, 1888;Uzawa and Higuchi, 2010). Downward penetration requires that the sporophyte elongates faster than the epigonium and that gametophytic tissues provide less resistance to expansion in the downward than upward direction.…”

“…The placental space is littered with cellular debris as cell walls disintegrate in advance of the sporophytic foot (Browning and Gunning, 1979a;Frey et al, 2001;Uzawa and Higuchi, 2010). This gross morphology suggests the aftermath of a struggle between the generations.…”

“…Considerable variation exists in the depth to which the sporophytic foot penetrates maternal tissues (Roth, 1969;Ligrone et al, 1993;Uzawa and Higuchi, 2010). The presence or absence of barriers to unfettered flow between maternal and offspring tissues is also variable.…”

“…Apoplastic continuity between gametophytic and sporophytic hydroids is present in Bryum capillare (Ligrone and Gambardella, 1988) and Funaria hygrometrica (Browning and Gunning, 1979c) whereas the two sets of hydroids are separated by a layer of sporophytic transfer cells in Timmiella barbuloides (Ligrone et al, 1982). The foot does not penetrate as far as the maternal vascular strand in other mosses (Uzawa and Higuchi, 2010).…”