Lauritz W. Olson

The synaptonemal complex and the spindle plaque during meiosis in yeast

Meiosis in Saccharomyces cerevisiae proceeds principally in the same manner as in other Ascomycetes. Leptotene is characterized by unpaired lateral components and pachytene by the presence of extensive synaptonemal complexes. The synaptonemal complex has the same dimensions and is similar in structure to those described for other organisms. Chromosome counts can now be made by reconstructing the synaptonemal complexes. Diplotene nuclei consistently contain a single polycomplex. The behaviour, doubling and the fine structure of the spindle plaque provide additional markers for the different stages of meiosis.

The meiospore ofAllomyces

SummaryThe arrangement of cellular organelles within the meiospore ofAllomyces macrogynus was found to be similar to the zoospore of this species, with the exception that the meiospore contains membrane enclosed electron dense reserve material which has the appearance of the gamma bodies observed in the zoospores ofBlastocladiella. The three dimensional structure of the side body complex is analyzed with serial sections and compared to homologous organelles in other members of theChytridiomycetes.

Polyploidy and its control in Allomyces macrogynus

The sporophyte of Allomyces macrogynus is an autotetraploid, which after meiosis produces a diploid gametophyte. After growth of the sporophyte for more than 6 months at 35°, or after growth on a substrate containing para-fluorophenylalanine (100 mg/1) at 35°, strains can be isolated which show a halving of the chromosome number, nuclear volume and DNA content/spore. The zoospores and meiospores also show an increased sensitivity to u.v. irradiation and these strains were shown to be diploid. If tetraploid resting sporangia are germinated in a solution of colchicine, meiosis is blocked so that no nuclear divisions take place and gametophytic thalli develop. When these gametophytic thalli are selfed, sporophytic colonies are produced with an increased ploidy, and these colchicine-induced polyploids are usually unstable.

Evidence for a male-produced pheromone inAllomyces macrogynus

Abstract A pheromone produced by the male gametes of Allomyces macrogynus has been partially characterized and given the name parisin. In chemotactic bioassays, parisin stimulated the attraction of female gametes but not male gametes or zoospores. Through several chemical treatments, it was found that parisin, an ether-soluble compound, is quite in that only acid/base hydrolysis inactivated the molecule (i.e., destroyed attraction). In these limited tests parisin showed the same characteristics as sirenin, the well-characterized pheromone produced by the female gametes.

Paternal inheritance of the mitochondrial dna in interspecific crosses of the aquatic fungus allomyces

SummaryWe have demonstrated by gel analysis of restricted DNA paternal inheritance of mitochondrial DNA in interspecific crosses between A. macrogynus and A. arbuscula.

The zoospore ofOlpidium brassicae

SummaryThe ultrastructure of the zoospore ofOlpidium brassicae is described and compared with observations made of other zoospores of the uniflagellatePhycomycetes. The zoospore ofO. brassicae is characterized by an extensive, cone-shaped rhizoplast and a lack of a nuclear cap, as well as a side-body complex or a rumposome. Vacuoles which contain osmiophilic material are termed gamma-like particles. Three-dimensional reconstructions based on serial sectioning were made of the organelles in the region of the nucleus, showing that the zoospore ofO. brassicae contains one or at most two elaborately branched mitochondria. Microbodies have a high degree of interconnection and are in intimate association with the mitochondrion, lipid drops, and the nuclear envelope.

A glass bead treatment facilitating the fixation and infiltration of yeast and other refractory cells for electron microscopy.

SummaryPhysical removal of the cell wall of yeast and other fungal cells, by rapid mixing of the cells with glass beads after preliminary fixation in glutaraldehyde or formalin, removes the cell wall barrier to fixation and/or infiltration of the cells for electron microscopy. The technique has been used on a variety of fungal cells which have been “difficult” to fix for electron microscopy, and appears to have wide applicability.

The zoospore ofPhlyctochytrium aestuarii

SummaryAn ultrastructural study of the zoospore ofPhlyctochytrium aestuarii Ulken is presented. It is shown to be almost identical to the zoospore ofP. sp., isolate 71-1-E, described byKazama (1972 a and 1972 b), the only significant difference in the ultrastructure of the zoospores being a less well developed “eyespot”-like complex in the isolate studied here, which correlates with an observed lack of phototactic response.In the description of the zoospore ofP. aestuarii emphasis is placed on the structure of the functional and vestigial kinetosome and on the position and composition of the “eyespot”-like complex. The latter is compared with related structures described from other posteriorly uniflagellate zoospores (belonging to the ordersChytridiales, Blastocladiales, Monoblepharidales andHarpochytriales) focusing on both the significant differences and on possible phylogenetic relationships.

The meiospore ofPhysoderma maydis. The causal agent ofPhysoderma disease of maize

SummaryThe meiospore ofPhysoderma maydis (Phycomycetes, Chytridiales, Physodermataceae) has a nuclear cap enclosing the cellular ribosomes within a double membrane, and double membranes traversing the nuclear cap. Aggregates of ribosomes not incorporated into the nuclear cap are also enclosed by double membranes. A vesicular network is observed in the anterior portion of the spore in direct connection with the nuclear cap membrane and with a stacked parallel array of membranes, which itself is connected with the nuclear cap membrane.The meiospore ofP. maydis contains a side body complex of the type observed in spores of theBlastocladiales. Vesicles enclose the side body complex and these vesicles are connected to the nuclear cap membrane and the nuclear envelope, and form a network which partially encloses the kinetosomal apparatus.The nuclear cap membrane, stacked array of membranes, and the vesicles which surround the side body complex and the kinetosomal apparatus contain an electron-dense amorphous material. On the basis of their ultrastructural appearance, these membranes are interpreted as part of a highly divided microbody.The ultrastructural organization of the meiospore ofP. maydis is compared to the structural organization observed in spores of theChytridiales, Blastocladiales, Monoblepharidales, andHarpochytriales. It is concluded that the structural organization of the meiospores ofP. maydis is the same as observed for members of theBlastocladiales, and it is suggested that thePhysodermataceae should be transferred from theChytridiales to theBlastocladiales.

Induction of abnormal male gametes and androgenesis in the aquatic PhycomyceteAllomyces

SummaryInduction of cleavage of the cytoplasm in the gametangium of a predominantly male strain of the aquatic PhycomyceteAllomyces under conditions of oxygen starvation, in the presence of dilute lactic acid, or dilute phosphate buffer, pH 7.0, resulted in multinucleate-multi-flagellate gametes. Under certain conditions the frequency for such abnormal gametes approached 70%. Phosphate buffer pH 7.0, at a concentration of 5 × 10−3-1×10−2 M and an incubation time of 90 minutes was found to be most effective in inducing multi-flagellate-multinucleate gametes. Nuclear fusion and multiple nuclear fusions were observed in these abnormal gametes as they developed into sporophytic thalli on dilute nutrient agar (YpSS/10). Multinuclear gamete development and nuclear fusion was analysed by electron microscopy. The reported observations reveal the occurrence of androgenesis from multinuclear male gametes inAllomyces.