1985 - Mycological Society of America

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26 and seasonal study (450 soil samples), Dictvostelium sohaerocephalum showed a positive response to pasturing when adjacent woods or old field are used for comparis011. A similar but less pronounced response was noted for 2. mucoroides. Polysphondilium violaceum had an opposite response. Polysphondilium pallidurn was found more frequently in the survey from pastures and old fields than from tilled fields, hay fields or woods. Both Dictvostelium discoideun and 2. polyceph- - alum were restricted to the undisturbed forest sites, while D. aureo-stipes and D. puroureum showed little or no response to agricultural treatment. Forest soil had the greatest diversity of dictyostelid species, followed by old fields, pastures, tilled fields and hay fields. The seasonal study indicated that fluctuations in total dictyostelid density closely follow fluctuations in the soil moisture through time and were most pronounced in soils of the woods and old field. The results demonstrate a possible role for the cellular slime molds as indicators of soil conditions which may be relevant for enhancing soil biological input into agricultural systems. T. M. HAMMILL, S. W. BEATTIE, and R. A. GRASSUCCI. SUNY-Oswego Laboratory for Ultrastructural Studies, SUNY College of Arts and Science, Oswego, NY 13126. Scanning electron microscopy of zyqosporogenesis in Mucor mucedo . -- Mated cultures of Mucor mucedo L. :Fr., NRRL 3634 (-) X NRRL 3635 (+), w - r m 10 C with a photoperiod of 12 h light alternatinq with 12 h darkness. Primary fixation for SEF! was done for 3 h in an unbuffered mixture of 2% ql utaraldehyde and 2% formal dehyde. Postfixation was in unbuffered 1% 0s04. Dehydration in ethanol was followed by transition to acetone and critical point drying in a Sorvall CPD System. The position of gametangial septa, formed after fusion of progametangial tips, was determined easily in SEM images. Suspensors, delimited as a result of gametangial septation, contained unequal amounts of protoplasmic contents, sugqesting that gametangia contribute disproportionately to zygospores. Branched micronyphae were observed commonly over the surface of developing zygospores. The outer wall of gametangia became ruptured and torn as the warty projections, characteristic of mature zygospores, developed from the underside, initially at the position of the fusion septum. Enlargement of zygospore initials was radial in the plane of the fusion septum. Then, zygospores enlarged toward gametangial septa. As a result , developing zygospores changed shape from oblong-ell iptical to spherical. Warty projections on zyqospores were conical with lonqi tudinal ridges. They commonly had remnants of ruptured wall material on their tips. T. M. HAMMILL, S. W. BEATTIE, R. A. GRASSUCCI, D. A. USSMAN, and C. T. WARE. SUNY-Oswego Laboratory for Ultrastructural Studies. SUNY Colleae of Arts and Science, Oswego, NY 13126. - ~ransmission electron microscopy of zygosporogenesis in Mucor mucedo. I. Early stages. Mated cultures of M. mucedo were grown as described above. Fixation fTr m s according to procedures published elsewhere by the senior author. Gametangia1 septa, which divided programetangia into gametangia and suspensors, contained numerous plasmodesmata connecting suspensors and gametangia. Gametangial septa developed an electron-opaque layer on the suspensor side. They also showed a variety of swellings. At the margins of gametangial septa, conspicuously thick- ened areas were formed, suggestive of a support function. The conical "warts," which ornament mature zygospores, were electron-opaque. They initiated as e- lectron-opaque thickenings in the developing zygospore wall,. "Mart" initials appeared on fusion septa, and it appears that fusion septa may only partially dissolve and then evaginate rather than dissolve completely. More work should clarify this. Zygospore wal! layers are deposited beneath qametangial wall layers which rupture as a zygospore inflates. "Wart" initials become confluent at their bases. Protoplasmic projections into regions between developing "warts" contained numerous vesicles, consistent with developmental models for wall deposition. Karyogamy appears to occur shortly after plasmogamy. Nuclei in prozygospores often were seen to have variable shapes and to contain microtubules. Zygospores developed numerous lipid qlobules. There is no evidence to date which supports a zygospore/zygosporangium dichotomy. Hammons, T. H., see Ellzey, (1. T., et. al. Harding, K., ,ee Pommerville, J., et. al. S. D. HARRIS and D. A. COTTER, Department of Biology, University of Windsor, Windsor, Ontario, Canada N9B 3P4. Characterization of Saccharmyces cerevisiae mutants unable to grow in trehalose containing media. Haploid vegetative cells of the yeast Saccharomyces cerevisiae contain two trehalase activities. The activity located in the cytoplasm has a neutral pH optimum and is responsible for the breakdown of endogenously synthesized trehalose. The activity located in the vacuole is active at an acidic pH value and has not been assigned a cellular function. We have found that growth of vegetative cells on exogenous trehalose induces the trehalase activity which functions at the acidic pH value. Cells grown on maltose, as well as stationary phase glucose grown cells also express this activity. We have isolated a mutant that does not grow on trehalose or maltose, and fails to express this enzyme activity. The mutant grows well on glucose and sucrose, but enters the stationary phase earlier than wildtype cells. Preliminary evidence indicates that the mutant is not impaired in trehalose transport. Arrested mutant cells appear to accumulate carbohydrate material in the vacuole. These results suggest that this vacuolar trehalase activity has a degradative function in glucose depleted cells, while being specifically induced by growth on trehalose or maltose. Harrison, J. A,, see Jaworski, A. J. Haskins, E. F., see McGuinness, M. D. E. F. HASKINS and M. D. McGUINNESS. Department o f Botany, University of Washington, Seattle, WA 98195. Light and electron microscopical studies on Semimorula liquescens. Semimorula 1 iquescens is a protoplasmodial slime mold which produces sessile fruiting bodies. We have recently discovered the occurrence of synaptonemal complexes during sporulation in this species. The possible taxonomic affinity of this organism with the Myxomycetes and Protostelia will be discussed. Heath, M. C., see Meyer, S. L. F.
W. M. HESS. Department of Botany and Range Science, Brigham Young University, Provo, UT 84602. Invaginations in plasmalemmas of grass smut teliospores (Ustilaqo bullata) viewed by stereo projection. Invaginations in plasmalemmas of U, bullata teliospores were studied by freeze-fracture procedures. More variation was evident in PF and EF surfaces when spores were wet for 13 hr than when spores were only wet for 6 min before freezing for f reeze-f racture. Plasma membranes of germinated spores which were not fixed prior to freezing had fewer disruptions than plasma membranes of spores which were germinated and fixed. If spores were germinated then desiccated before freezing for freeze-fracture, membrane disruptions were less severe than when spores were germinated then fixed before freezefracturing. The only treatment which made it possible to get consistent images of both PF and EF plasma membrane surfaces was desiccation followed by wetting spores only 6 min before freezing for freeze-fracturing. Hinton, D. M., see Racon, C. W. WILLIAM E. HINTZ, JAMES B. ANDERSON, PAUL A. HORGEN Dept. Botany, Univ. Toronto, Erindale Campus, Mississauga, Ont. L5L 1C6. Mitochondria1 inheritance in Agaricus bitorquis. We have used polymorphisms in mitochondrial (mt) DNA restriction patterns as phy:ical markers to examine organelle inheritance in crosses between sexually compatible strains of Agaricus bitorquis. When two sexually compatible monkaryotic strains are paired, a fluffy zone of mycelium appears at the confluence of the two cultures. The cells in the fluffy zone are predominately dikaryotic. Usually the zone of dikaryotic hyphae remains at the line where the cultures meet; nuclear migration generally does not occur in Agaricus. However, a variant strain (Ag 8-11 donates nuclei that migrate in the mycelium of some compatible mates following hyphal anastomosis. In a series of crosses between Ag 8-1 and compatible mates the mitochondrial types of the compatible mates predominated in the dikaryon formed after nuclear migration from Ag 8-1 had occurred. A dikaryon (Ag 471, resulting from crossing the variant Ag 8-1 with a recipient strain Ag 34-2, carries the same mtDNA and mitochondrial plasmids as strain Ag 34-2 as determined by mtDNA restriction analysis, however the copy number of the three Ag 34-2 mitochondrial plasmids is greatly increased in the dikaryon (Ag 47). This suggests that in strains isogenic for mtDNAs plasmid copy number is influenced either by the nuclear genotype or by the nuclear status (monokaryotic vs dikaryotic) of the strain. H. H. HO. Department of Biology, State University of New York, NY 12561. The validity of Phytophthora melonis and P. sinensis. -- Phytophthora melonis was erected by Katsura (1968) as the causal agent of foot rot of cucumber in Japan. It was characterized by semi-papillate, non-proliferating sporangia and chlamydospores. Since then, a similar disease known as dieback, root rot, crown rot or blight was reported on various cucurbits in Egypt, Iran, Taiwan and the 2 7 mainland of China, but the pathogen was identified as p. drechsleri, p. melonis or p. sinensis sp. nov. 9 comparative study of these isolates with the type or authentic cultures of p. drechsleri, g. melonis and p. sinensis was conducted and they were found to be similar in cultural, morphological and pathological characteristics. The original description of p. melonis was inaccurate and misleading, because upon re-examination, the type culture produced distinctly non-papillate and internally proliferating sporangia in water and chlamydospores could not be found. Since P. sinensis was erected solely based on comparison with Katsura's erroneous description, the new epithet is not warranted. When studied under similar cultural conditions, neither -- P. melonis nor p. sinensis was specifically distinct from p. ,drechsleri. Thus, to avoid further nomenclatural confusion, both p. melonis and p. sinensis should be treated as synonyms of p. drechsleri which has priority. Hocking, A. D., see Pitt, J. I., et. al. Horgen, P. A., see Hintz, W. E., et. al. Horgen, P. A., see Horton, J. S. Horgen, P. A., see rleyer, R. J., et. al. P.A. HORGEN. Mushroom Research Group, Univ. of Toronto, Erindale Campus, Mississauga, Ont. L5L 1C6 Biotechnological Approaches to Mushroom Strain Improvement, Are They Possible? Three unique plasmid-like DNA components were isolated from a strain of Agaricus bitorquis. The DNA moieties were linear, possessing regions of terminal inverted repeated sequences. Plasmid-like DNAs have been observed in a number of wild Agaricus isolates; no plasmid-like DNAs have been found in cultivated strains of A. bisporus. No homology was detected between the plasmids and the nuclear or mitochondrial genomes of either wild or cultivated Agaricus. The three plasmids are distinctly different and appear to independently replicate. Restriction fragments of the mushroom plasmids have been cloned. Inorgennello transcription and translation of Agaricus mitochondria will determine if the plasmid DNA sequences carry any expressed genetic information. Transformation strategies using antibiotic resistance genes and mushroom plasmid origins of replication will be discussed. Heterologous hybridization approaches have been used to isolate specific gene sequences for both nuclear and mitochondr ial genes for Agaricus. These sequences will provide a preliminary gene bank for Agaricus. Mitochondria1 DNA studies indicate that considerable restriction pattern heterogeneity exists in the wild Agaricus while none exists in the cultivated Agaricus. The genome size of A. bitorquis is twice that of A. bisporus. Preliminary evidence suggests that mitochondrial genome type and mushroom plasmid copy number may be under nuclear control. The feasibility of using recombinant DNA approaches to genetically alter the commercial mushroom will be discussed. J.S. HORTON and P.A. HORGEN. Department of Botany, Erindale Campus, Univ. of Toronto, Mississauga, Ont. L5L 1C6. The steroidal regulation of gene products in Achlya. The addition of antheridiol to undifferentiated cultures of Achlya elicits several changes in macromolecular syntheses during the ontogeny of antheridiol branch initials. There is an enhancement of
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1985 - Mycological Society of America

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