The fine structure of septal pore apparatus in the lamellae of Pholiota terrestris

The lamellae of Pholiota terrestris, when viewed in thin sections cut perpendicular to the hymenial surface, consist of a hymenial layer of basidia and scattered cystidia, an interwoven subhymenium, and a trama. The inner trama is composed of a zone of relatively large, vacuolated hyphal elements, whereas the outer trama consists of smaller hyphal elements with relatively dense cytoplasmic contents. The septal pore apparatus throughout the lamellae are similar to those described in most other Homobasidiomycetes and saprobic Heterobasidiomycetes. In the center of the septal pore there is a narrow electron-dense zone that intersects the pore canal. In some septal pores similar electron-dense zones occur near one or both orifices. The septal cap consists of three membranes, of which the two defining membranes appear clearly tripartite in cross section. The pores in the septal cap are arranged hexagonally and are 70–105 nm in diameter. The proximal septal caps of the subbasidial septa and those in the subhymenium develop an electron-dense, granular outer cap that is usually delimited externally by endoplasmic reticulum or, less often, by the tonoplast of an adjacent vacuole. The septal pores of the subbasidial septa become plugged by the expanded septal swelling following basidiospore discharge. The septal pore apparatus in the trama are not associated with outer caps; however, many septal pores in the trama become occluded with electron-dense plugs near both orifices. The observations of the septal pore apparatus in the lamellae of P. terrestris are compared with studies of other Homobasidiomycetes and saprobic Heterobasidiomycetes.