Formation of Pollen Exine Bacules and Microchannels on a Glycocalyx

Abstract

In Epilobium and Chamaenerion a glycocalyx, containing mucopolysaccharides, is present between the plasma membrane and outer surface of the tectum during the microspore period. The glycocalyx is built up by rod-shaped units. The orientation of these rods is roughly perpendicular to the cell surface although their traces are vermiculate. The early accumulation of exine material occurs between the rod-shaped regions containing mucopolysaccharide material. Eventual encirclement of the rods with exine material results in the formation of cylindrical channels, of extremely uniform size, common to most Onagraceous pollen exines. Although use of the terms primexine matrix or template exine is avoided in this report, they are unquestionably useful and can be applied in the absence of the histochemical data necessary for defining a glycocalyx. They delimit an ontogenetic period and a space, however, whereas a glycocalyx might be expected to be present throughout development and across the entire sporoderm, including the primexine matrix, oncus of apertural regions and intine. The term glycocalyx has the further advantage of carrying with it an association of a number of functions suggested by an extensive literature, e.g., recognition mechanisms, immunological reactions, cellular differentiation, intercellular attachment, formation of cuticular layers, and ion exchange. Glycocalyces are specializations of the plasma membrane, the importance of which may be found to lie in the mediation of genetic control over exine form.