CYTOPHOTOMETRIC MEASUREMENT OF NUCLEAR DNA IN SEVEN HETEROTHALLIC ISOLATES OF DIDYMIUM IRIDIS,A MYXOMYCETE

Absorption cytophotometry was used to measure nuclear Feulgen-DNA content of myxamoebae and Plasmodia in seven heterothallic isolates of Didymium iridis. Measurements of myxamoebal nuclei from clones of four isolates (Hon 1, Pan 1, Pan 2, and CR 5) gave a mean DNA value of 0.34, whereas the nuclei of Plasmodia which develop from each of the four intraisolate crosses had a mean value of 0.63. These values correspond to the 2C haploid level in myxamoebae and the 4C diploid level in Plasmodia. DNA values in two additional isolates (Pan 3 and CR 2) are much higher than the mean for the other five. Accordingly, it is proposed that these may be polyploid. The question of polyploidy in D. iridis and in other myxomycetes is evaluated. The seventh isolate, Ky 1, is taxonomically very close to D. nigripes and was not included in calculations of mean values for D. iridis.     

COMPARATIVE MEASUREMENTS OF NUCLEAR DNA IN A HETEROTHALLIC AND A SELF-FERTILE ISOLATE OF THE MYXOMYCETE,DIDYMIUM IRIDIS

Comparative measurements were made of the nuclear Feulgen-DNA content of a heterothallic and a self-fertile isolate of the myxomycete Didymium iridis. Plasmodial nuclei of both isolates contain the diploid amount of DNA. The replicated diploid (4C) values for the heterothallic and the self-fertile isolates are 5.66 and 5.95, respectively. Myxamoebae, however, are quite dissimilar in their nuclear DNA content. Those of the heterothallic isolates, Honduran 1–2 (A¹) and Panamanian 2–4 (A⁷), have mean values of 3.81 and 3.69, whereas myxamoebae of the self-fertile Philippine-1 isolate were found to have a mean value of 6.07. Myxamoebae of the Ph-1 isolate are, therefore, at the same ploidy level as the Ph-1 Plasmodium. Mean DNA values for Ph-1 sporangial nuclei were in category 4C. Measurement of the DNA content of mitotic metaphases in sporangia at T = 6 hr confirmed that the mean DNA content of both Ph-1 myxamoebae and plasmodial nuclei is equivalent to 4C. It is concluded that nuclear phase alternance is lacking in the Ph-1 isolate and that the Plasmodium of this isolate develops by apogamy.     

NUCLEAR DNA CONTENT OF MYXAMOEBAE AND PLASMODIA IN SIX NON-HETEROTHALLIC ISOLATES OF A MYXOMYCETE,DIDYMIUM IRIDIS

The nuclear DNA content of six non-heterothallic isolates of the myxomycete Didymium iridis was measured by combining the Feulgen reaction with absorption microspectrophotometry. This allowed us to distinguish between homothallic (sexual) and apogamic (non-sexual) isolates. Four of the isolates studied, Panamanian 4 and 5, California 1, and Missouri 1 are homothallic. Moreover, the average DNA content of the myxamoebal and plasmodial nuclei (0.32 and 0.61 respectively) does not differ significantly from the calculated haploid and diploid values for heterothallic isolates of D. iridis (0.34 and 0.63). Hence, it is concluded that in each of these isolates the myxamoebae are haploid and the plasmodia diploid. In two of the isolates investigated, Georgia 1 and Hawaii 1, the DNA content of the myxamoebal and plasmodial nuclei did not differ significantly. Therefore, in both of these isolates the plasmodia appear to develop apogamically. In addition the mean DNA values recorded for the Ha-1 isolate suggest that it is aneuploid.     

A MORPHOMETRIC ANALYSIS OF CYTOLOGICAL CHANGES DURING SPORE MATURATION IN THE MYXOMYCETE DIDYMIUM IRIDIS

Ultrastructure of spore maturation in the myxomycete Didymium iridis was investigated using morphometric analytical techniques. Changes in actual volume (μm³) and relative volume (Vv) of nuclei, autophagic vacuoles, mitochondria, microbodies, lipid droplets, and spore wall were described for spores in three stages of development. Stage I spores were newly formed, surrounded only by the cell membrane. Stage II spores were approximately 1 hr older than Stage I spores and possessed surface spines, but little if any additional wall material. Stage III spores were 24 hr old and possessed a fully formed, multilayered wall. The results of this study indicate that spore maturation in D. iridis is a multistep process involving a decrease in spore volume and coordinated changes in specific organelle compartments. From Stage I to Stage III, mean spore volume decreased by more than 50%. Percent volume data (Vv) showed that Stage I spores allocated volume equally to all measured organelles except microbodies and the spore wall, the latter of which had not yet begun to develop. By Stage II, only the nucleus and spore wall showed significant changes in Vv values, both increasing. In terms of actual volume, the nucleus, autophagic vacuole and spore wall increased by Stage II. Between Stages II and III the cell wall was the only component to increase in volume, all others decreased in volume. Our data indicate a close relationship between a decrease in organelle volume and an increase in cell wall volume in the Stage III spore. The autophagic vacuole and the cell wall dominated the volume of the Stage III spore while the remaining volume was allocated unequally to the other components.     

QUANTITATIVE MICROSPECTROPHOTOMETRY OF NUCLEAR DNA IN SELFING STRAINS OF THE MYXOMYCETE DIDYMIUM IRIDIS

Genetic and cytochemical investigations of the origin, development, nuclear activity, and ploidy level of Plasmodia obtained from selfed clones S-2 and B₁P-33 of the heterothallic myxomycete, Didymium iridis, are presented. To demonstrate that selfing did not result from contamination of the clones, or mutations at the mating-type locus, crosses were made between F₁ clones and clones of known mating types. The data were inconsistent with these two possibilities. DNA was quantified by Feulgen-DNA microspectrophotometry. All cellular phases studied (logarithmic amoebae, swarmers, and encysted amoebae) appear to be haploid, with the nuclear DNA being in the replicated (2C) state. The plasmodia are in all cases diploid; however, the data indicate that the selfed Plasmodia are in an extended G₁ condition. The nuclear DNA content of these is therefore 2C, whereas that of the cross Plasmodium is 4C. Sporangial nuclei exhibit DNA in diploid replicated (4C) category.     

FURTHER STUDIES IN MULTIPLE ALLELOMORPH HETEROTHALLISM IN THE MYXOMYCETE DIDYMIUM IRIDIS

Analysis of an isolate of Didymium iridis from Costa Rica indicates that it possesses a pair of incompatibility factors. These factors have been shown to be allelic with those of a Honduras and a Panama isolate. Data presented in this paper show that, among them, the 3 isolates possess 6 incompatibility alleles at 1 locus.     

MULTIPLE ALLELES AT THE INCOMPATIBILITY LOCUS IN THE MYXOMYCETE DIDYMIUM IRIDIS

Collins , O'Neil Ray . (Queens Coll., New York City.) Multiple alleles at the incompatibility locus in the Myxomycete Didymium iridis. Amer. Jour. Bot. 50(5): 477–480. 1963.—Working with 2 isolates of Didymium iridis, from Honduras and Panama, respectively, it was shown that each isolate possesses a pair of incompatibility factors. On the basis of results from inter-isolate crosses, one pair was designated A¹ A² and the other A³ A⁴ to indicate that these factors actually constitute a series of multiple alleles at a single locus.     

CYTOPLASMIC INCOMPATIBILITY STUDIES IN THE MYXOMYCETE DIDYMIUM IRIDIS: RECOVERY AND NUCLEAR SURVIVAL IN HETEROKARYONS

At least eleven somatic compatibility loci exist in the myxomycete Didymium iridis. Cell fusion is controlled by at least seven fusion loci (Fus1–Fus7). Cytoplasmic compatibility is controlled by at least four clear-zone loci (Cz1–Cz4). Plasmodia with identical phenotypes at all seven fusion loci, but different phenotypes at the clear-zone loci, will fuse temporarily, but fusion is soon blocked by cytoplasmic reactions which prevent complete mixing. Areas which contain cytoplasm from two incompatible Plasmodia become clearly delineated from healthy cytoplasm. Such areas, termed clear zones, have been isolated and found to recover. If clear zones are sectioned into several small pieces, not all pieces will recover, indicating that toxic cytoplasmic reactions have occurred. Plasmodial fusion studies and F₁ studies of recovered clear zones indicate that the clear-zone loci may also control nuclear survival in heterokaryons.     

CONTROL OF PLASMODIAL FUSION IN A PANAMANIAN ISOLATE OF DIDYMIUM IRIDIS

Plasmodial fusion in a Panamanian isolate (Pan. 1) of Didymium iridis is controlled by at least six fusion loci. Only plasmodia with identical phenotypes for these six loci are capable of fusion. No evidence was obtained in this study to indicate that any one fusion locus more strongly affects the fusion process than any of the other loci. Control of plasmodial fusion in the Pan. 1 strain of D. iridis is similar to that found earlier for a Honduran strain (Hon. 1).     

GENETICS OF SOMATIC CELL FUSION IN TWO ISOLATES OF DIDYMIUM IRIDIS

Analysis of progeny from a cross between a Honduran clone and a Panamanian clone of Didymium iridis has revealed existence of five new plasmodial fusion loci in the Panamanian isolate. These are in addition to six which were previously known.     

HETEROTHALLISM AND HOMOTHALLISM: A STUDY OF 27 ISOLATES OF DIDYMIUM IRIDIS,A TRUE SLIME MOLD

Single pore studies of 27 isolates of Didymium iridis from several geographical locations revealed that 11 are heterothallic, displaying a one-locus, multiple allelic mating system. Collectively, 9 of the 11 possess a total of 12 mating types in one multiple allelic series. Each of the remaining two isolates has a pair of mating types which are either incompatible with the 12 or they have not yet been tested against them. Sixteen isolates proved to be homothallic.     

GENETICAL AND CYTOLOGICAL EVIDENCE FOR CHROMOSOMAL ELIMINATION IN A TRUE SLIME MOLD,DIDYMIUM IRIDIS

In crosses involving a polyploid myxamoebal clone. CR 2-25*, F₁ plasmodia and myxamoebae display a variety of unexpected ploidy levels as indicated by nuclear DNA measurements. Genetic analyses of the F₁ generations reveal either complete elimination of certain genetic markers or greatly skewed segregation ratios. On the basis of these two kinds of evidence, it is assumed that chromosome elimination occurs at some stage (or stages) following karyogamy between parental nuclei. The possible significance of polyploidy in relation to myxomycete speciation and evolution is discussed.     

A NEW,HETEROTHALLIC SPECIES OF SORDARIA

Olive , L. S., and A. A. Fantini . (Columbia U., New York, N. Y.) A new, heterothallic species of Sordaria. Amer. Jour. Bot. 48(2): 124–128. Illus. 1961.—S. brevicollis, sp. nov., was isolated from zebra dung from the New York Zoological Park. It is the only species of the genus that has been found to be heterothallic and to have microconidia. The latter function readily in fertilization. Heterothallism is controlled by a single allelic pair of compatibility factors located about 14.2 crossover units from the centromere. Incomplete mating reactions involving this species, Gelasinospora autosteira, and Neurospora crassa indicate relationships among these 3 genera.     

中国有壳肉足虫(原生动物)五新纪录描述

描述了采自云南、湖北和广东的5种有壳肉足虫,隶属原生动物亚界,肉鞭门,叶足纲,表壳目,均为国内新纪录种:非游巧装表壳虫Arcella artocrtea aplanata Grospietsch,1954;具角肋表壳虫A.costata angulosa (Perty) Playfair,1918;拟普通盘状表壳虫A.discoides pseudovulgaris Deflandre ,1928;光滑弯凸表壳虫A.gibbosa laevis Deflandre ,1928;球形叉口砂壳虫Difflugia gramen globulosa Stěpánek et Jirí,1958.     

TESTATE AMOEBAE FROM THE EARLY JURASSIC OF THE WESTERN TETHYS,NORTH‐EAST ITALY

Abstract: Fossil testate amoebae and their non‐marine finds are rare so their ecological importance through Earth history is poorly understood. The Lower Jurassic shallow water black‐shales of Trento Platform (north‐east Italy) are rich in micro‐organisms and contain a thecamoebian and ostracod assemblage representing the first known record of Early Jurassic oligohaline forms from the European mainland. The thecamoebians are represented by the genera Difflugia, Pontigulasia and Centropyxis. The present discovery of Lower Jurassic thecamoebians in fine carbonate organic‐rich deposits indicates, for the first time, that these sediments can preserve testate amoebae very well. The occurrence of difflugid testate amoebians confirm a transitional marine‐terrestrial habitat, outside large bodies of water, and suggests occasional eutrophication in ephemeral restricted aquatic environment in the Sinemurian–Pliensbachian Trento Platform.     

GROWTH AND DEVELOPMENT OF THE MYXOMYCETE PERICHAENA VERMICULARIS. II. CHROMOSOME NUMBERS AND NUCLEAR CYCLES

Chromosome counts of dividing nuclei of the myxomycete Perichaena vermicularis indicate a number of 25 ± 2 in the amoebae and 50 ± 4 in the Plasmodia, confirming earlier reports that amoebae are haploid and plasmodia diploid. Chromosome numbers obtained from nuclei during sporangial development indicate a fluctuation in the location of meiosis influenced by environmental conditions. The implications of these observations are discussed in reference to past conflicting evidence of the location of meiosis.     

SOME CULTURAL AND GENETIC ASPECTS OF A NEW HETEROTHALLIC SORDARIA

Fields , William G., and James Maniotis . (Wayne State U., Detroit, Mich.) Some cultural and genetic aspects of a new heterothallic Sordaria . Amer. Jour. Bot. 50(1): 80–85. lllus. 1963.— Sordaria heterothallis sp. nov., isolated from rabbit dung collected in Austin, Texas, is characterized as a spermatium-prcducing, hcterothallic Sordaria with carbonous stromatic walls. Spermatia may germinate, but their low frequency of germination suggests their role in asexual reproduction is minor. The fungus was determined to be biotin- and thiamine-deficient. A single pair of factors about 1.9 units from the centromere governs compatibility. Ordered tetrad analyses indicates regular segregation of factors for ascospore germination, the production of aerial mycelium and pigmentation. Intra- and intergeneric reactions stimulating protoperithecial production occurs between Sordaria heterothallis and the related species Sordaria brevicollis and Gelasinospora atilosleira.