No abstract

Mitosis and the phylogeny of Taphrina. Can. J. Bot. 60: 1696-1725.Details of mitosis are described by serial-section electron microscopy of synchronized yeast-phase cultures of five species of Taphrina. Based primarily on the morphology and behaviour of the nucleus-associated organelles (NAOs) and modes of spindle formation we conclude that three species are typical ascomycetes which have some significant differences in their mitotic systems. Each of two cultures of a fourth species, T. deformans, was apparently a mixed culture. An ascomycete type of mitosis was shared by cells of both cultures, but one culture also had cells with another ascomycete mitotic system characterized by elaborate and unique NAOs, whereas other cells of the second culture contained a basidiomycete mitotic apparatus. The fifth species contained a typical basidiomycetous mitotic system, which indicates that it is misidentified. The detailed differences among the mitotic systems of the true Taphrina species suggest that the genus as a whole is polyphyletic but undoubtedly ascomycetous. However, a previously unreported pattern of spindle formation found in three species is only otherwise known in a red alga, which may support a common ancestry for the red algae and the ascomycetes. New observations pertinent to the mechanisms of mitosis include, in various species, ( a ) evidence for splitting of NAOs, and their attendant spindle microtubule arrays, during prophase, (b) spindle microtubule polymerization adjacent to the nuclear envelope prior to NAO insertion into the envelope, and ( c ) presence of only two to four nonkinetochore microtubules during anaphase-telophase.

Sporulation in four species belonging to three different families of the Hemiascomycetes is described from serial sections. The results show that in each species the formation of the ascospore wall is initiated at a specialized spindle pole body. Spore delimitation proceeds concurrently with the last nuclear division in the ascus. The findings support the taxonomic position that these species belong to a group that includes the yeasts but that is distinct from the Euascomycetes.

The hermaphrodite snail Helisoma duryi reproduces preferentially by cross-fertilization. Virgin and castrated snails lay an insignificant number of egg masses. The fine structure of its endocrine dorsal bodies (DB), which regulate reproduction, has been studied in reproductively inactive virgin and castrated snails and in reproductively active mated snails, using tannic acid staining and autoradiography after injection of L3Hlleucine. The DB cells of the mated snails appear synthetically active, containing scattered rough endoplasmic reticulum (RER) and probably smooth endoplasmic reticulum (SER), many Golgi complexes, and putative DB hormone-containing granules. On the other hand, the DB cells of the virgin and castrated snails appear synthetically inactive, containing RER in circular stacks, few Golgi complexes, many lipid droplets, and scattered glycogen. Mitochondria appear slender in mated snails, whereas those in virgin and castrated snails appear large and spherical. With tannic acid treatment, the processes of the DB cells of mated snails exhibited more released granules than those of virgin and castrated snails. Many silver grains were seen on RER, Golgi complexes, and mitochondria in the autoradiographs of the DB cells of mated snails. It is suggested that the DB cells of the reproductively active snails are synthetically more active than those in virgin and castrated snails and that the DB cells may produce peptide hormone as well as a steroid hormone.

The morphology and the organization of the endocrine dorsal bodies (DB) of non-reproducing virgin and castrated, and reproducing mated Helisoma duryi have been examined using serial sectioning. The DB cells occur in two masses on the mid-dorsal side of the cerebral commissure, each of which has a cortical zone containing the cell bodies and a medulla where cell processes terminate. The cell bodies measure 10-15 μm in diameter, and are arranged in lobules of 6-12 cells. The complex cell processes are winding and terminate at various distances from their cell bodies in both reproducing and non-reproducing snails. Few 70-90-nm membrane-bound granules are found in the cell bodies and many are seen in the cell processes, which seem to penetrate the perineurium of the cerebral ganglia and make close contacts with neurosecretory cells. In reproducing snails the DB cells display a significantly larger amount of plasma membrane sproutings in the form of loops and circles compared to that in reproductively inactive virgin or castrated snails. Images of thin-sections and freeze-fracture replicas of these membranes suggest that they are gap junctions, which join the DB cells with each other. It is likely that gap junction-mediated cell to cell communication is involved in the activation of the DB cells for their role(s) in reproduction.