Ultrastructure of plasmodesmata and cross walls inCephaleuros, PhycopeltisandTrentepohlia(Chroolepidaceae; Chlorophyta)

Abstract

Cross walls in Cephaleuros, Phycopeltis and Trentepohlia contain simple plasmodesmata approximately 40–50 nm in diameter. In all three genera, the plasmodesmata generally occur in only the central portion of the cross wall, thus forming a “central pit”. In the cross walls between vegetative cells of Phycopeltis, a ring of lightly stained material within a thickened border encircles the central pit. The cross walls between vegetative cells in Cephaleuros and Trentepohlia specimens examined thus far clearly lack the distinct arrangement characteristic of Phycopeltis; however, the cross walls between the zoosporangium and pedicel (i.e. the zoosporangium-pedicel septa) in Cephaleuros, Phycopeltis and Trentepohlia contain an inner ring of wall material which encircles the central pit. Despite some similarity between such septa and the cross walls of Phycopeltis vegetative cells, the latter are morphologically distinct. Ultrastructural observations clearly indicate that the central pits of the Chroolepidaceae are unlike the pit connections of some Rhodophyta and any intercellular connections which may occur in the Cyanophyta.