Development of the Zygospore Wall in Rhizopus sexualis (Smith) Callen

Abstract

SUMMARYAs the zygospore of Rhizopus sexualis enlarges it develops a thick wall. Studies with the transmission and stereoscan electron microscopes show that this wall is formed in the following manner. (I) The gametangial septa increase in thickness by the deposition of new material, which is laid down more rapidly on the inner or zygospore side than on the suspensor side. These septa form the 'end walls' of the zygospore. Fine plasmodesmatal tubules remain at intervals in the wall and are in direct connexion with the tubules of a dense zone of endoplasmic reticulum situated on either side of the septa. It is considered likely that the plasmodesmata allow the passage of nutrients from the parent hyphae into the developing zygospore. (2) The 'side wall' of the zygospore is formed by the development of new patches within the original wall of the fused gametangia. At first these 'patches' are shaped like inverted saucers and are separate from each other, except that there is a more continuous zone adjacent to the end walls of the spore. Then, the 'patches' become larger, by the deposition of new material at the rim, finally becoming shaped like inverted flower pots and coalescing at the rims to give a continuous warted layer. Until this stage the zygospore wall is permeable to water and dissolved substances. Meanwhile the original wall h s t becomes gelatinous, then membranous, and finally tears and is sloughed off exposing the newly-formed sculptured wall. (3) Finally a new inner wall, impermeable to water and dissolved substances, is laid down within the ornamented wall.

Further Investigations of Actinomycetes by Scanning Electron Microscopy

“…The technique has now been successfully applied to a variety of microbes. Studies include an ever-increasing number on fungi (Barnes & Neve, 1968;Greenhalgh & Evans, 1968;Hawker, 1968;Hawker & Gooday, 1968;Jones, 1968;Old & Robertson, 1969). Bacillus endospores have been examined by Murphy & Campbell (1969), bacteria in soil by Gray (1967) and Hagen, Hawrylewicz, Anderson, Tolkacz & Cephus (1968), blue-green algae by Echlin ( I 968), and protozoa by Small & Marszalek (1969).…”

Azygosporogenesis in Mucor azygosporus

“…(Hawker and Gooday 1968) and Rhizopus sexualis (Hawker and Beckett 1371) suggest that this layer may consist of several closely adpressed layers. These observations need to be confirmed by transmission electron microscopy.…”

“…The gametangial septum of Mucor azygosporus is similar in genesis and structure to that produced by other mucoraceous fungi during normal sexual reproduction (Hawker and Gooday 1968 ;Hawker and Beckett 197 1 ;O'Donnell et al 1976aO'Donnell et al , 1977 in that it (1) develops rapidly by the centripetal coalescence of prealigned vesicles and (2) is perforated by plasmodesmata. As in R. sexualis (Hawker and Beckett 1971 ;Beckett et al 1974) and G. persicaria (O'Donnell et al 1977), secondary thickening of the gametangial septum in M. azygosporus is asymmetric towards the gametangial side.…”

An unusual specimen of the enigmatic fungal reproductive unit Windipila spinifera from the Lower Devonian Rhynie cherts of Scotland

“…II, fig. 20;Hawker and Gooday 1968;Hawker and Backett 1971;O'Donnell et al 1978). Rather, the interior sphere is somehow reminiscent of the single oil globules that are visible in the zygospores of, for instance, certain representatives of the mucoralean genera Radiomyces (Radiomycetaceae; e.g., Embree 1959: figs 12, 13;Benny and Benjamin 1991: figs 8, 16, 18, 29h, i) and Dichotomocladium (Lichtheimiaceae; e.g., Benny and Benjamin 1993: fig.…”