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.     

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.     

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.     

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.     

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.     

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).     

RECIPROCAL TRANSFER OF MATERIALS BETWEEN ALGAL CELLS AND MYXOMYCETE PLASMODIA IN INTIMATE ASSOCIATION

Zabka , George G. (U. Iowa, Iowa City), and Waldo R. Lazo . Reciprocal transfer of materials between algal cells and myxomycete plasmodia in intimate association. Amer. Jour. Bot. 49 (2) : 146–148. Illus. 1962.—Pure cultures of Fuligo cinerea, a myxomycete, and Chlorella xanthella, a green alga, were separately permitted to accumulate sodium radiophosphate from an agar medium and come into full association with non-radioactive cultures of the other organism. Manipulation of such mixed cultures indicates that a Plasmodium of Fuligo cinerea and vegetative cells of Chlorella xanthella are both able to absorb radiophosphorus from a nutrient medium and transfer it to each other. It is suggested that these phenomena support the possibility of a symbiotic relationship between the alga and myxomycete in association.     

SOMATIC CELL INCOMPATIBILITY IN DIDYMIUM IRIDIS: LOCUS IDENTIFICATION AND FUNCTION

Somatic incompatibility in two strains of the myxomycete Didymium iridis is controlled by at least 13 loci: seven fusion loci and six clear-zone loci. Details on correlating loci of the Hon 1 strain with Pan 1 loci are given and a unified nomenclature, applicable to both strains, has been developed from data presented in this paper. Although fusion loci generally prevent fusion between different plasmodial incompatibility phenotypes, studies on individual loci have shown that a limited transient fusion may occasionally take place. Thus, the differences between the fusion and clear-zone loci are not as distinct as once thought. However, the 13 somatic incompatibility loci are still easily designated as either fusion or clear-zone loci, and no locus has thus far been found with true intermediate function. Studies on individual locus function are also discussed.     

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.     

NUCLEAR DNA CONTENT IN POPULATIONS OF PINUS RIGIDA

Five populations of Pinus rigida growing in contrasting ecological situations ranging from North Carolina (35°53'N latitude) to Quebec (45°06'N latitude) showed no significant variation in amounts of nuclear DNA with respect to germinating seedlings. Nuclear volume of dormant nuclei also showed no significant variation between and within populations, a finding that is consistent with the concept that the basic 2C DNA value of Pinus rigida is uniform under all habitats. This finding is in contrast to numerous reports for other coniferous species.     

膀胱肿瘤DNA含量、核形态学特点与AgNORs计数的研究

应用图像分析技术对４３例膀胱肿瘤细胞ＤＮＡ含量和核形态参数进行了定量测定,同时进行核仁组成区（ＡｇＮＯＲｓ）计数研究,结果表明：肿瘤细胞的ＤＮＡ含量及干系水平与组织学分级基本一致,ＤＮＡ含量及干系水平越高,则恶性程度越高,ＤＮＡ含量与核面积及核最短直径的变化里正相关性,与ＡｇＮＯＲｓ的计数无明显相关性。这三项检测方法对肿瘤生物学行为判断均有重要的参考价值。     

FLOW-CYTOMETRIC ANALYSES OF NUCLEAR DNA CONTENT IN FOUR FAMILIES OF NEOTROPICAL BATS

Flow-cytometric analyses of 29 species of microchiropteran bats representing four families and 20 genera revealed that bats possess only 79% (5.43 pg) of the DNA content of a “typical” mammal (e.g., Mus musculus strain C57BL; 7 pg). Chiroptera, the second largest order of mammals, is thus an exception to the prevailing view that mammals possess a minimum nuclear DNA content of 7 pg. Limitations on cell size resulting from a high metabolic rate may have constrained evolution of DNA content and could explain why the extensive heterochromatic additions that are common in some groups of mammals are absent in bats. Chromosomes of bats have been well studied; detailed chromosomal banding data are available for nearly all the species used in this investigation. However, no significant correlations were found between DNA content and karyotypic characteristics such as 2n, fundamental number, and rate or pattern of chromosomal evolution.     

RELATIONSHIPS BETWEEN CELL CYCLE DURATION, S-PERIOD AND NUCLEAR DNA CONTENT IN ERYTHROBLASTS OF FOUR VERTEBRATE SPECIES

Erythroblasts of four vertebrate species (Triturus cristatus, Rana esculenta, Lacerta viridis and Gallus domesticus) differing markedly in their nuclear diploid DNA content, are used to study a possible relationship between cell cycle duration and DNA content. DNA is determined cytophotometrically and fluorometrically. The cell cycle is analysed by evaluating labelled mitoses after an injection of tritiated thymidine and also by double labelling with ¹⁴C- and ³H-thymidine. A direct but non-linear relationship is demonstrated between DNA content of erythroblast nuclei and the duration of DNA-synthesis.     

DROUGHT STRESS RESPONSES OF MICROSERIS SPECIES DIFFERING IN NUCLEAR DNA CONTENT

Anatomical and physiological responses to drought stress were compared in two Microseris species differing in DNA content and originating from contrasting habitats relative to water availability (M. bigelovii, DNA = 2.6 pg nucleus^–1, more xeric; M. laciniata, DNA = 6.8 pg nucleus^–1, mesic). Leaf mesophyll cell volume was positively correlated with DNA content and negatively correlated with tissue elasticity, i.e., low ϵ̄ and thin cell walls. Drought stress increased leaf tissue elasticity (lower ϵ̄, thinner cell walls). Cell volume, cell wall thickness, cell number, and leaf area were decreased most by drought stress in M. laciniata. Osmotic adjustment with a 20% increase in total solutes (mostly amino acids) after stress was observed in both species, but their estimated contribution to the change in osmotic potential was larger in M. bigelovii. These findings indicate that the Microseris species studied respond to low water availability by maintaining turgor with 1) small cell volumes, 2) elastic tissues (low ϵ̄, thin cell walls), and 3) osmotic adjustment. Both enhanced tissue elasticity and small cell volume appear to be inherent characteristics in M. bigelovii and drought-induced responses in M. laciniata. These data are compatible with the hypothesis that natural selection may influence DNA content through differential sensitivity of cell growth to environmental stress.     

VARIATION OF NUCLEAR DNA CONTENT IN HELIANTHUS ANNUUS (ASTERACEAE)

Nuclear 2C DNA content was determined by laser flow cytometry for 13 diploid (2n = 34) lines (cultivated varieties and inbred lines) of Helianthus annuus. Mean DNA amount of second leaf nuclei varied from 6.01 to 7.95 pg (32%) among lines. Mean DNA content varied up to 19% within lines. Variability in mean DNA content exceeding 27% and 48% was detected among leaves from different nodes of plants of the open-pollinated variety, Californicus, and the inbred line, RHA 299, respectively. The root tip and shoot tip nuclei of H. annuus have been reported to consist of a mixture of aneuploid (17 to 33 chromosomes) and diploid (34 chromosomes) cells, a condition called aneusomaty. Chromosome counts of root tips and an analysis of the distribution of DNA content of large numbers of nuclei from leaves indicate that aneusomaty either does not occur, or is not common, among the lines investigated. The intraspecific, intraline, and intraplant variation in DNA content in H. annuus support the concept that a sizable portion of a plant genome is unstable and subject to rapid changes in DNA amount.     

DURATION OF MITOSIS AND SEPARATE MITOTIC PHASES COMPARED TO NUCLEAR DNA CONTENT IN ERYTHROBLASTS OF FOUR VERTEBRATES

The passage of a wave of tritiated. thymidine-labelled cells through each of the phases of mitosis is analysed in erythroblasts of four vertebrates species, selected because of their widely differing diploid DNA content. Mitotic time (t_m) and relative durations of separate mitotic phases as well as that of the G₂ period are thus accurately determined. Mean duration of t_m appears to vary according to the species specific DNA amount. This relation is approximately the same as for S, for G₁ and for the generation time, which have been previously determined.     

THE NUCLEAR DNA CONTENT OF DEVELOPING BARLEY ALEURONE CELLS

The nuclear DNA content of developing barley aleurone cells was examined by Feulgen cytophotometry using the Cytophotometric Data Conversion (CYDAC) system. At no time in their development did aleurone cells exhibit a single peak corresponding to the triploid (3N) amount of DNA. Although considerable heterogeneity was observed at every stage of development, the mean nuclear DNA content approximately doubled from the earliest to the most mature stage.     

SOME OBSERVATIONS ON DNA CONTENT AND CELL AND NUCLEAR VOLUME GROWTH IN THE DEVELOPING XYLEM CELLS OF CERTAIN HIGHER PLANTS

List , Albert , Jr . (Douglass Coll., Rutgers U., New Brunswick, N. J.) Some observations on DNA content and cell and nuclear volume growth in the developing xylem cells of certain higher plants. Amer. Jour. Bot. 50(4): 320–329. Illus. 1963.—The developing metaxylem cells of Acorus calamus roots undergo an over-all growth in cell and nuclear volume that may be expressed roughly as a constant ratio of relative growth rates. Within this over-all growth picture, however, there is a periodicity of both nuclear and cell volume growth. Other plants such as Peltandra, Eleocharis, and Dennstaedtia undergo a similar volume growth. Marsilea tracheary elements have an increase in nuclear number per cell by simultaneous divisions. Arisaema metaxylem nuclei go through a series of DNA doublings correlated with nuclear volume doubling and cell volume increase, at least up to the 16- or 32-ploid level. The cells display some tendency to fall into size classes, expressing a pulsation in growth. A fluctuating alternation or stepwise growth of cell and nucleus appears to describe the data more suitably than the allometric growth equation. In Zea, the cell and nuclear volumes for metaxylem cells fit a fluctuating envelope better than the straight line, and there is again the probability that cell volumes fall into size classes related to nuclear volume class. The DNA content of the nuclei was determined to fall into a frequency distribution having peaks at the 4-, 8-, 16-, and 32-ploid equivalent, agreeing with an earlier report for diploid maize. DNA content was highly correlated with nuclear volume in the over-all growth of the metaxylem cells.