SPORE WALL DEVELOPMENT IN THE LIVERWORT FOSSOMBRONIA WONDRACZEKII (CORDA) DUM.

Abstract

  Spore wall development in Fossombronia wondraczekii (Corda) Dum. is centripetal, beginning with the deposition of a distinctly patterned spore special wall around the young spores of the tetrad. This special wall appears to function as a primexine in which the pattern of the mature outer layer of exine is established during the early tetrad stage. Neither the common sporocyte wall or the special wall stained for callose. Next, an inner layer of exine is initiated by the production of tripartite lamellae (TPL) at the surface of the plasma membrane. The TPL form separate shallow discs of several layers which closely invest cytoplasmic lobes. Both the TPL discs and the underlying plasma membrane stain intensely with phosphotungstic acid-chromic acid. The discs of the TPL accumulate and compress into one or two continuous multilaminar bands. Sporopollenin impregnates the outer homogenous sculptured exine and the multilaminar bands of inner exine. The innermost layer of fibrillar intine is the last wall layer to be initiated. Developmentally, the Fossombronia spore wall represents a distinct type within the Metzgeriales and has no clear homology to other hepatic spores studied. The primexine-like spore special wall of Fossombronia differs from the preprophasic wall precursors in Pallavacinia, Haplomitrium and Apotreubia in that it is deposited in the tetrad stage and is non-callosic in nature. On the basis of spore wall ontogeny, the Metzgeriales appears to be a heterogenous assemblage.