Nuclear membranous whorls

Summary Membranous whorls have been seen in the nuclei of peritoneal and testicular cells which had been subjected to various experimental manoeuvres. It seems likely that this is an early manifestation of cell degeneration which is demonstrated readily only by glutaraldehyde fixation, and to that extent can be regarded as a glutaraldehyde artifact. Acknowledgements. This work was supported by grants from the Medical Research Council, and the University of Sheffield Tuberculosis Research Fund, and by a grant to the Department from Unilever Ltd.I am grateful to Professor R. Barer for his advice and criticism, to Dr. G. A. Meek for guidance on electron microscopy, to Dr. E. J. Clegg for permission to use material from joint experiments. Technical and photographic assistance was provided by Messrs. P. GarLick and L. Murgatroyd and by Miss M. Tune.     

Division of the primary nucleus ofAcetabularia

Summary The division of the primary nucleus ofAcetabularia mediterranea, andAcetabularia cliftonii was studied by light microscopical observation of living cells. Nuclear and nucleolar volumes are reduced when the caps of the cells have reached their maximum diameter. When the nucleus has reached a size of about 30–50 m in diameter, condensed chromosomes are formed which are separated by an intranuclear spindle.     

Ultrastructural features of the life cycle ofAcetabularia mediterranea

Summary The portion of the life cycle ofAcetabularia mediterranea from cyst formation to gamete release is described. During maturation, the cyst nucleus undergoes a series of mitoses in which the nuclear membrane remains intact, and the spindle microtubules are confined to the intranuclear space. There is a dark requirement for the completion of cyst maturation at the end of which the nuclei are in groups and centrioles are present. The final migration of the nuclei, cleavage of the cytoplasm into gametes, and the development of flagella is cxtremely rapid, taking six to twelve hours. Cysts which fail to germinate are blocked at a late stage in the maturation process, either before or after the final nuclear division.The observations are related to mitosis in other green algae (Chlorophyceae) and to gametogenesis inBryopsis hypnoides. Changes in the amount and distribution of heterochromatin in the nuclei are discussed in relation to the life cycle ofA. mediterranea.The substance of this paper was first presented orally at the Symposium onAcetabularia held at the Max-Planck-Institut für Zellbiologie, Wilhelmshaven, Federal Republic of Germany, July 12–15th, 1972.Supported in part by Grant GM 06637 from the U.S. Public Health Service.     

The role of the cell-apex in elongation ofAcetabularia

Summary Exposure of only the apical portion of anAcetabularia cell to light causes the cell to elongate as much as cells which are totally illuminated. No elongation takes place if only the apical portion of the cell is kept in the dark.In totally illuminated cells, preferential exposure to DCMU of the apical region only also inhibits cell elongation.Local-photosynthesis in the apical region might be essential for elongation. The participation of other photomorphogenetic reactions in the apical region are not excluded.     

The flagellar root system in the gamete ofAcetabularia mediterranea

Summary Ultrastructural investigation of the flagellar root system ofAcetabularia gametes reveals one type of organization for both male and female gametes. There is a modified cruciate system with four microtubular bands X-2-X-2, with X=4. A prominent distal striated fiber and a small proximal striated fiber connect the flagellar bases. A striated root fiber type I underlies the microtubular root type II, and a short striated root fiber type I underlies the microtubular root type I (terminology ofMelkonian 1980 b). This specific root system has some details in common with theChlamydomonas type, and others with theUlvaphyceae and the siphonalean algaeDerbesia andBryopsis. This might indicate the phylogenetic relationships.     

Multinuclear stages of the life cycle ofAcetabularia mediterranea

Summary The reproductive stages of the life cycle ofAcetabularia mediterranea have been studied in Feulgen-stained material. Light-microscopical photographs of secondary nuclei, cyst formation, gamete formation, gamete release, zygote formation and early development of the germlings are presented. The time course of cytological events during gamete formation is described. Mitoses are found between 16 and 24 hours after the induction of cyst germination.The author is indebted to Mrs. S.Artelt who helped with the prepration of the specimens and the photographs.     

Subclassification of spiral monocentric whorls

Despite all the papers on the classification of dermatoglyphic features, there is no definitive in sight yet. With this work we intend to contribute to adapt the subclassification of spiral monocentric whorls to their biologic nature. The results in this work show that clockwise whorls on the right hand match counter-clockwise ones on the left, and counter-clockwise spirals on the right are joined together with clockwise on the left. We propose the building of two new subclasses of spiral monocentric whorls to replace the traditional ones in order to conserve the bilateral identification of these pattern types.     

Morphology of the nucleo-cytoplasmic interactions during the development ofAcetabularia cells

Protoplasma - An electron microscopic survey of nuclear events and changes in the perinuclear cytoplasm during the generative phase ofAcetabularia is presented with details on late stages in the...     

Current-voltage relationships of potassium channels in the plasmalemma ofAcetabularia

Summary The outer membrane of mechanically prepared protoplasmic droplets fromAcetabularia mediterranea has been investigated by patch-clamp techniques. These membranes are shown to consist of physiologically intact plasmalemma. With the Cl^– pump inhibited, microscopic currents through K⁺-selective channels were studied. These currents compare well with macroscopic K⁺ currents as previously determined by standard microelectrode techniques and tracer flux measurements. There is about one K⁺ channel per m² in the plasmalemma. The current-voltage relationship (I–V curve) of the main open channel (channel A) is sigmoid over a voltage range between about –100 and +100 mV with saturation currents of about ±10 pA. A second species (or different state of channel A) of K⁺-selective channels (channel B) differs from channel A by smaller saturation currents (about ±7 pA) and a much smaller open probability. The open probability of channel A increases from almost zero at large negative voltages to about 1/2 at large positive voltages. Taking the closed times into account, the mean steady-stateI–V curve of channel A displays outward rectification about the equilibrium voltage for K⁺ and negative slope conductance at larger negative voltages. The open channelI–V curve of the open channels A and B, the changes of theI–V curve of the open channel A upon variation of the external K⁺ concentration, as well as the mean steady-stateI–V curves of channel A are described by simple reaction kinetic models, the parameters of which are determined to fit the experimental data. The results are discussed with respect to data from other K⁺ channels in plants and with respect to regulation of the cytoplasmic K⁺ concentration inAcetabularia.     

Ridge course of the whorls: Classification and methods

In dermatoglyphic methodology the system of gross classification of digital pattern types needs modifications. More attention should be focussed on the study of minute morphological variations among pattern types in order to understand fully the genetic mechanisms involved in pattern variations. A systematic classification to record many of the morphological peculiarities is lacking. This paper proposes a classification and methods of identification of the direction of the course of the ridges inside the pattern area of true whorls. In all, nine ridge course types are identified, named and described. Data analysed on the basis of the above methods and classification reveal significant bilateral differences for clockwise and counter-clockwise types of ridge directions. Mode of inheritance, bisexual differences, etc., of the polymorphic course of these ridges should be studied. Its usefulness in the field of personal identification, population genetics and medicine should also be evaluated.     

SEPALLATA gene diversification: brave new whorls

SEPALLATA (SEP) genes form an integral part of models that outline the molecular basis of floral organ determination and are hypothesized to act as co-factors with ABCD floral homeotic genes in specifying different floral whorls. The four SEP genes in Arabidopsis function redundantly, but the extent to which SEP genes in other flowering plants function similarly is unknown. Using a recent 113-gene SEP phylogeny as a framework, we find surprising heterogeneity among SEP gene C-terminal motifs, mRNA expression patterns, protein-protein interactions and inferred function. Although some SEP genes appear to function redundantly, others have novel roles in fruit maturation, floral organ specification and plant architecture, and have played a major role in floral evolution of diverse plants.     

RNA Synthesis in isolated living and fixed nuclei ofAcetabularia

Summary Isolated, gently fixed nuclei ofAcetabularia mediterranea are capable of incorporating nucleotides into RNA. This has been demonstrated by (a) sensitivity of the synthesized products to RNase, (b) inhibition of RNA synthesis by actinomycin D and (c) incubation of nuclei without CTP and GTP. Experiments with -amanitin show that at least two RNA polymerases are active in isolated fixed nuclei. Also isolated, living nuclei incorporate nucleotides into RNA. RNA synthesis was located autoradiographically and quantified by a TV-analysator.     

Rhoptry secretion of membranous whorls by Plasmodium berghei sporozoites

Electron microscopy of sporozoites of the rodent malaria parasite, Plasmodium berghei, reveals electron-dense multilaminate membranous whorls within components of the rhoptry-microneme complex after fixation with tannic acid in conjunction with glutaraldehyde. This multilaminate material, which has a dark line to dark line periodicity of approximately 5 nm, appears to be secreted from the sporozoite since it is also found adhering to the sporozoite's external surface. The material may function in sporozoite gliding motility and in invasion of host cells.