The cytoplasmic granules of Hydrodictyon reticulatum were studied by electron microscope. Four kinds of granules were distinguished. Large dense granules (0.5-0.75μ in diameter) and small dense granules (0.1-0.25μ in diameter) were regarded as the so-called spherosomes and prespherosomes respectively. But these two types of granules are not thought to be organellae with a specific roles in the cell because no definite internal structure could be distinguished. Besides these granules, small dense particles which have similar dimensions to Palade granules and rod-shaped mitochondria which have microvilli were seen. The present results are consistent with those obtained in our previous work.
1. Tetraploidy was induced in Rauvolfia serpentina (2n=22)-a plant of considerable medicinal importance. 2. Aqueous colchicine solution of two different concentrations viz. 0.25 and 0.5 per cent were applied on cotton wad around stem tip at seedling stage. Both the concentrations responded well to seedling treatment but 9 hrs. treatment with 0.5 per cent gave maximum tetraploids. 3. Colchicine affected shoots were mostly sectorial chimeras, but some were more or less complete tetraploid for all practical purposes. 4. Immediate effects of colchicine on the treated shoots were arrested stem elongation, leading to the enlargement of the treated regions. Tetraploid branches were slow growing and somewhat shorter but sturdier. 5. Leaves were shorter in length but wider, thicker and darker green. The increased thickness was shared both by the palisade and spongy tissues. Stomata were larger and fewer per unit area. 6. Flowering was delayed in the tetraploid plants. Number of flowers per inflorescence was less in the tetraploids and this criterion was quite significant in Rauvolfia serpentina. 7. The flowers and floral parts showed a marked tendency towards decrease in length, but increase in diameter or width. 8. Change in pollen sterility was found to be invariably associated with induction of tetraploidy. Pollen grains were larger in size with remarkable change in their morphology. Number of apertures varied with the shape. Tetraploid pollen grains were mostly quadrangular or pentangular in shape. 9. Number of fruits and seeds in tetraploid Rauvolfia plants was significantly reduced. 10. The mean frequency of quadrivalents per cell was 4.8. Irregular distribution, precocious movements, lagging chromosomes and supernumerary spored quartets were seen in Rauvolfia. 11. Though most of the parts of Rauvolfia exhibited gigas habit the utility of the tetraploids is yet to be determined by growing the progeny of the tetraploids and estimating the alkaloid contents of the roots of mature plants.
The pollen and seed fertility status of 75 clones of Vetiveria zizanioides (Linn.) Nash collected from different parts of India was assessed as an essential prerequisite for the formulation of a rational programme of improvement. In view of the surprisingly high pollen sterility in some of the clones, a preliminary cytological study of microsporogenesis in four clones of differing fertility was undertaken. It appeared that univalent formation at diakinesis and metaphase and lagging at anaphase resulting in the elimination of chromatin material was closely correlated with the observed sterility.
The morphology and contents of each type of blood cell present in Pseudentys scripta elegans as seen in the electron microscope have been described, compard and illustrated. Each granulocyte is a distinct cell type and no transitional forms are seen. The adult turtle red cell, unlike its mammalian counterpart, contains the basic cytoplasmic and nuclear components of any cell.
1. The development of chloroplasts in normal and in chlorophyll-deficient yellow lethal (y11y11) specimens of the soybean (Glycine max (L.) Merril) was studied with the electron microscope. 2. The steps in the differentiation of normal soybean chloroplasts are similar to those found in other seed plants, ferns and mosses, namely: (1) the formation of vesicles from the inner of the two membranes of the proplastids, (2) the construction of primary lamellae by the fusion of the vesicles, (3) the building up of discs and the aggregation of the discs to form grana, (4) the increase in the number of grana and their interconnection by stromatic lamellae. 3. In the development of the chlorophyll-deficient chloroplasts of the mutant, vesicle formation and fusion of vesicles to form primary lamellae appear to proceed normally in the proplastids; sometimes grana are formed. But either the arrangement of the lamellae in the later stages of development is abnormal, or the lamellae break down and vacuolization of the chloroplast ensues.
The chromosomes of O. australiensis were made up partly of heterochromatin whereas those of O. sativa were almost of euchromatin. In the F1 hybrid of O. sativa×O. australiensis, there was differential condensation in these two morphologically different types of chromosomes. The ones with partly heterochromatin and partly euchromatin condensed early starting off presumably from pachynema on till diakinesis. Whereas the ones with only euchromatin seemingly started their condensation later but condensed more complete at first metaphase. Thus before diakinesis the australiensis chromosomes were darker in staining and were 2-4 times the size of the sativa chromosomes at MI-AI. At either diakinesis or MI-AI, about two bivalents could be found per PMC. These bivalents could be separated into two types at MI-AI by size, or by difference in taken up the stain at diakinesis: 1. autosyndetic 2. allosyndetic (multivalents were also found only very rarely) All these bivalents were proved to be authentically true bivalents. The evidences were: 1. There were loosely paired chromosomal segment observed repeatedly in many PMC's at pachynema. 2. At diplonema, allosyndetically paired bivalents were found to have one chiasma mostly, or two or more chiasmata in some PMC's. 3. At diakinesis, these allosyndetically paired bivalents were found to be ring-shaped as well as the end-to-end ones. 4. Closed allosyndetic bivalents with two chiasmata were frequently observed at MI-AI. Pairing of the homologous segments in these allosyndetic pairs was assumed to be carried out at the euchromatic regions of the two chromosomes concerned. Presumably, these euchromatic regions of the chromosomes from two different species might have same rate of condensation at various stages of meiosis.
Cytological observations on intercrosses between stocks of maize interchanges involving the same chromosomes with different break points showed that at pachytene homologous terminal segments usually were paired whether the configurations were “pairs” or associations of four chromosomes. The intercalary segments showed extensive non-homologous association or asynapsis. In the crosses studied in which the break points were in opposite arms in both chromosomes, “pairs” in which the homologous intercalary segments including the centromeres were paired were never found. Hence, pairing usually began at the ends of the chromosomes, although it started, or occurred at the same time occasionally at other points along them. The intercalary segments were at a great disadvantage in pairing. The centromere played no apparent significant role in initiating pairing. In certain intercrosses the frequent failure of pairing in the short terminal segment translocated to another chromosome was correlated with complete pairing in the adjacent region, indicating the importance of regions near but not at the end in controlling the pairing behavior. Association initiated between two homologous regions continues to proceed along the chromosomes in a zipper-like manner, often bringing about an association of non-homologous parts, until it is prevented by a counter association from the opposite direction. The results of limited genetic linkage tests and spore quartet analyses of crossing-over frequencies showed that regions in which there was usually non-homologous association or asynapsis were characterized by reduced or no detectable crossing-over, whereas in a region that usually was paired, crossing over was essentially normal.
1) In der vorliegenden Arbeit wurden die Chromosomen der Mitose von Isoetes asiatica untersucht. Der Karyotypus dieser Art läßt sich als K=11 (n)=2V (H1 H2)+4V+4J+j feststellen. 2) Die negative Heteropyknose des Heterochromatins wurde zuerst bei den Pteridophyten in den metaphasischen H1- und H2- Chromosomen dieser Art wahrgenommen. 3) Der Karyotypus von Isoetes asiatica müsse wohl aus solch einem Karyotypus 6 (n)=3V+3J, - wie z. B. Anthoceros, der einer sekundäre Grundkaryotypus von Bryophyten zu betrachten ist, dadurch herrühren, daß der 3V+3J-Satz sich zuerst gerade verdoppelte und dann davon das eine Chromosom zwischen den verdoppelten beiden kleinsten J-Chromosomen ausgeschieden wurde. Nachschrift. Die vor kurzem erschienene Mitteilung von Á. Löve (Cytotaxonomy of the Isoetes echinospora Complex. Amer. Fern. J. Vol. 52, No. 1, 1962) konnte hier leider nicht berücksichtigt werden.
1. Detailed cytological analysis at diakinesis and metaphase I in Zebrina pendula Schnizl., (n=12) showed that about 47.65% of the cells examined contain higher associations of rings and chains of 6 and 4 and chains of 3 chromosomes. More than two such higher associations per cell or more than 6 chromosomes per association were not observed. The rest of the chromosomes formed into bivalents and univalents. 2. The differences in the sizes of the chromosomes in the higher associations, pachytene configurations with cross-shaped figures and formation of associations of 6's in a plant showing only a tetraploid chromosome number confirm that these higher associations are formed as a result of reciprocal translocations between nonhomologous bivalents. 3. Univalents formed as a result of failure of chiasma formation or nondisjunction of higher associations at anaphase I either divided or undivided reach the poles or lag behind and organize into micronuclei which were usually met with from dyad stage to pollen grains. 4. Bridges with or without fragments were found in a low percentage of cells at anaphase I and II and telophase I and II. Pollen sterility is very high. 5. The divergent cytological behaviour of Z. pendula investigated by various workers is believed to be due to geographical variations under the influence of which the plants of this species are undergoing chromosome evolution with differential rapidity by spontaneous structural rearrangements in the somatic chromosomes. 6. Colchicine induced tetraploid Z. pendula (n=24) formed mostly bivalents and this prevalent bivalent pairing was explained in terms of preferential pairing between the exactly identical partners of chromosomes furnished by the duplicate genome. This suggests that all the chromosomes in the diploid are structurally dissimilar to some extent or other and in the absence of completely homologous partners the unlike chromosomes resort to pairing in the diploid.
1. The chromosome number and karyotype of distinct North American Polygonatum species, i.e., P. pubescens and P. commutatum, were studied cytologically on Wisconsin material. 2. All P. pubescens plants proved to be diploid with 2n=20 chromosomes, with their karyotype referable to the latifolium-type previously described by Therman (1950). 3. Two different clones of P. commutatum were examined, viz., one each of the “typical” and “giganteum” type. Both were tetraploid with 2n=40 chromosomes, with the nearly identical karyotypes characterized by three pairs of chromosomes (Nos. 3, 4 and 8) with a secondary constriction. 4. On the basis of chromosome morphology, the tetraploid P. commutatum is nearly identical to a double P. pubescens (i.e. the latifolium-type) except that the characteristic chromosome pair 4 of P. pubescens is only once represented in the tetraploid karyotype (pair 8), its mate (pair 7) lacking the secondary constriction. 5. The basic karyotype of the Wisconsin tetraploid plants of P. commutatum is not clearly referrable to the latifolium-type, as one would expect on the basis of simple doubling, although it was reported as such by Therman. 6. The possibility need not be excluded that P. commutatum has a different basic karyotype.
An electron microscopic study on the localization of ATP-splitting enzyme in the rat thigh muscle was undertaken with the application of the section freeze substitution technique of Chang and Hori. Enzyme activity was localized as electron-opaque, lead phosphate precipitates, by means of the modified Wachstein and Meisel method. Reaction product was found within the A band, excluding the H band, as well as in vesicular and tubular elements, including trials, of the sarcoplasmic reticulum (SR). Its localization was also demonstrated in mitochondrial membranes.