Karyotypic studies based on squash preparations of regenerating contourfeathers have been made in two species of birds. Euodice cantans has a diploid chromosome number of 76±2 and Emberiza flaviventris one of 82±. The Z-chromosome of E. cantans is metacentric and ranges as number four. The W-chromosomes could not be identified.
Growing roots of onion were treated with solutions of ISDA a new compound of plant origin for 1-4 hours and frequencies of different stages of mitosis were determined immediately. A sudden reduction of mitotic index was noted even after 1 hour's treatment with 0.005 %, while 0.02 % fully inhibited the cell division after 4 hours of treatment. A prophase to anaphase ratio showed that there is an appre-ciable amount of prophase inhibition and inhibition of the spindle which results in the polyploid nuclei. Cytological studies revealed abnormalities like bridges with or without fragments and a considerable number of polyploid cells. In second experiment the growing roots were treated with 0.02% ISDA for three hours and allowed to recover for different durations upto 120 hours. It was seen that the inhibition on frequency of division lessened as the period of recovery increased. A number of cytological aberrations were encountered. These included bridges, micronuclei, pycnotic masses, fragments and laggards. Stickiness of chromosomes was pronounced throughout the treatment. However, following a recovery period of 120 hours it was seen that most of the abnormalities disappeared and frequency of normal cells increased correspondingly.
To understand the mechanism of variation of chromosome numbers in the progeny of triploid guava, the cytological and other aspects were investigated. Due to autotriploid nature of the seedless guava, the association of chromosomes at met. I varied considerably, which in turn had profound influence on anaphase I separation. The separation pattern at ana. I with 14-19 chromosomes was highest (24%), and lowest in 8-25 separation (2%). The frequency of all the chromosomes going to one pole was 6 percent. Although the stainability of pollen grains were 44 percent in triploid, they were ineffective in fertilization. The progeny raised from open pollinated seeds were, therefore, the result of pollination from diploid plants. From the frequency of observed and expected progeny, the gametic selection was inferred. The gametes with very high and low chromosome numbers appeared to be eliminated, as no plant beyond 34 somatic chromosome numbers were observed in the progeny. The frequency of occurrence of more plants with 22 and 24 somatic chromosomes clearly supported the theory of gamete selection.
Cytological observations on anomalous salivary chromosomes of D. parasaltans showed some features presented to discuss their filamentous structure. The abnomally large size plus the loose structure of such chromosomes allowed us to base our observations on pictures taken through the optical microscope.
Fine structural aspects of interphasic parotid gland cell nuclei treated with pilocarpine or atropine were the subject of observation. Pilocarpine caused an increase of the amount of interchromatin and perichromatin granules and a slight electrondensity of the interchromatinic substance. Atropine, on the other hand, caused a decrease or disappearance of perichromatin granules, an increase of the amount of interchromatin granules and electrondensity of the clumps of chromatin and interchromatinic substance, and the folding of the nuclear membrane. The authors described for the first time the occurrence of the so-called interchromatin canaliculi in the atropinized nuclei.
Intraplant variation in chromosome numbers have been reported in the somatic cells of S. officinarum, pollen grains of S. spontaneum and microsporocytes of S. officinarum×S. spontaneum hybrids. The origin of the chromosome mosaics has been traced to the spindle abnormalities caused by genetic factors in the case of S. officinarum, unequal numerical distribution or elimination of univalents during meiosis in S. spontaneum and disturbances in the pre-meiotic mitosis in the interspecific hybrids. It is concluded that the alteration in chromosome numbers in the cells of individual plants followed by vegetative propagation and the functioning of pollen grains with varying chromosome numbers might have played a significant role in the evolution of the extensive euploid-aneuploid series reported in S. spontaneum.
The kinetics of postnatal cerebellar neurogenesis in chicks was studied by 3HTdR autoradiography. Results suggest that DNA synthesis occurs mainly in the external granular layer. After a premigratory period of 2 to 3 days in the external granular layer, cells begin to migrate and give rise to nuerones of the molecular and internal granular layers and to glial cells of the white matter. During the premigratory period most cells from the external granular layer are dividing; however 10 to 15% of cells seem to be able to migrate without any previous division. In the chick, a precocious species, postnatal cerebellar neurogenesis seem to pro-ceed at a slower rate than in altricial species such as mice and rats.
1. Chromosome numbers for 33 collections belonging to 28 species and 25 genera from ten different tribes are reported. 2. Results of cytological study in 13 species were discussed in detail, since these were either studied for the first time or gave new counts or else showed other features of cytological interest. 3. Dysploidy was found to be common feature at the intraspecific level. 4. Polyploidy, as well as ascending and descending dysploidy seemed to have played an important role in evolution of the taxa discussed.
G1 cells in primary roots of Hordeum vulgare were gamma-irradiated with a dose of 198 R and centrifuged for 4 min at 1500×g at various time after irradiation. Post-irradiation centrifugation increased the frequency of anaphase fragments. The significant increase in frequency was found to be possible only before the progression of the irradiated cells from G1 into S. The best hypothesis to account for the obtained results seems to be that the G1 cell in the first mitotic cycle after seed germination does not contain the factor(s), probably enzyme(s), necessary to accomplish repair of radiation-induced lesions and also chromosome duplication.
Seeds and seedlings of Glycine max variety Biloxi and C. max variety UPI have been treated with aqueous solution of colchicine. Seedling treatments have been found to yield tetraploid plants in both the varieties. In the tetraploids, deformed, thick and dark green leaves, stunted growth, delayed flowering, changes in size and frequency of stomata and pollen grains and reduced fertility have been observed and discussed with reference to previous observations. More than three leaf-lets have been observed in the tetraploids and the size of the leaf-lets has increased. C1 generation has also been studied. Meiotic studies in the tetraploid revealed different combinations of uni-, bi-, tri- and quadri-valents with tetraploid number of chromosomes. Exact doubling of chromosomes was observed in comparatively few cells. PMCs with complete set of chromosomes involving quadrivalent formation have not been observed. Occurrence of high frequency of bivalents has been discussed. Maximum number of quadrivalents has been found to be six.
Protomyces macrosporus Unger pathogenic on Coriandrum sativum L. becomes systemic in the host stem much before or during the pre-flowering period, inducing organogenic changes in the flowers and fruits due to hypertrophy and hyperplasy. Micro- and megasporogeneses are inhibited and generative cells destroyed by the pathogenic diffusate. Partial fruit development due to part infection occurs variously and the chlamydospores in the pericarp are carried to the soil with the seed as a fresh inoculum.
The cytogenetic behavior of colchicine-induced reciprocal translocations in Collinsia heterophylla (Soriano 1957) is known to be different from those of radiation-induced ones (Garber and Dhillon 1962). This paper presents cytogenetic data on thirteen radiation-induced translocations in the same species in two (X2 and X3) generations. All translocations studied had two nonhomologous chromosome pairs involved. Most of the translocation heterozygotes showed directed orientation of the interchange complexes at metaphase I in both the X2 and X3 generations. RT-M showed random orientation and RT-N and RT-P displayed reversal from directed to random orientation or vice versa in these generations. These data combined with metaphase I chromosomal configurations observed for the various translocations indicated that RT-M resulted from breaks in the terminal or sub-terminal chiasma-forming regions of the two chromosome pairs involved (behavior similar to that of colchicine-induced translocations of Soriano). The rest of the translocations had breaks in the internal non-chiasma forming regions. While the breaks in RT-Q and RT-R2 may have been just proximal to the chiasma-forming regions, the breaks in the remaining translocations appear to be nearer the centromere than the chiasma forming segments. Thus two types of translocation behavior reported earlier for two different mutagens were observed in the present study involving gamma irradiation alone and the results in general support the underlying mechanical hypothesis for the random versus the directed types of orientation proposed earlier by Garber and Dhillon for C. heterophylla. However, genetic factors may also influence the orientation of the interchange complexes at metaphase I.
Analysis of metaphases for satellite associations from women taking oral contraceptives and control women showed a significantly higher incidence of these associations in the former subjects. There was also a significantly higher frequency of D-D associations in those women taking the “pill” compared to their controls. These abnormalities were not transmitted to the progeny.
Cytoenzymological reactions for SDH, LDH, Iso-CDH, G-6-PDH and cytochrome oxidase activity were tested on unfixed cultures of chick-embryo fibroblasts. The cultures were not passaged and the basic medium was unchanged throughout the experiment. The authors found that the enzymatic activity in the cells changes and increases with ageing of the culture within the fourth and sixth day. On the sixth day the activity disappears because of regressive changes in the cells. The observed individual differences in intensity of the enzymatic reactions in individual cells of the same kind and within the same culture result from various metabolic states of these cells.
With a view to finding out the inter-relationships between different 30 chromosome species of the genus Linum, 14 interspecific hybrids involving 8 species were obtained and studied morphologically and cytologically. The interspecific hybrids were studied for salient morphological characters of agronomic importance such as tillering, height, number of secondary branches, seed size besides hybrid vigour and seed fertility. They were also studied for their chromosome pairing and chiasma frequency in the pollen mother cells. The hybrids showed varying degrees of pollen sterility inspite of their chromosomes pairing and separating regularly. This indicated that the divergence of these species has progressed on either genic differentiation or cryptic structural differences. The species L. floccosum and L. palliscence differed from the rest in forming a single quadrivalent. This shows that these species differ from one another by a single reciprocal translocation. Based on chiasma frequency all the hybrids can be grouped into two categories, those forming more or less equal number of chiasmata as the parental species and those forming less than the parents. Suitable interpretations are advanced to explain the reduction in chiasma frequency in some hybrids under study. Probable cytogenetical mechanisms underlying species differeniation in the genus Linum are discussed.
Karyotype analysis in fifteen varieties of Lens culinaris was carried out. The varieties differ from each other in chromosome morphology and in total chromatin length. For much detailed studies D2 statistics was applied. According to D2 values the varieties were placed at nine different clusters. From the analysis of chromosome morphology and D2 values, it was revealed that variety formation in Lens culinaris has taken place due to structural changes in the chromosomes. It has also been accompanied by change in total chromatin length in different varieties. The SAT-chromosomes appear to have undergone changes as regard the position of secondary constriction, (NP varieties). In Russian and EC varieties they have not been recorded at all.
In M1, the PMC showed abnormalities, which appeared to have increased with dose, and they persisted through out the development of the shoot. In M2 the PMC with aberrations were far fewer than in M1, but their presence in M2 shows that they have been perpetuated through the male and female gametes of M1 generation. The types of aberrations recorded were translocations, bridges, micronuclei, pairing difficulties and pollen abnormalities. The low fertility following high doses in M1 plants, may be attributed to the phenomenon of chromosomal aberrations and change in the nature of the gene, thereby, creating pairing difficulties. The persistence of abnormalities in M2 generation indicates, that they may either take considerable time to be eliminated or they might have become a permanent feature of the plants.
Barley root meristematic cells were treated with three antibiotics known as the inhibitors of protein synthesis, i.e., chloramphenicol (CAP), cycloheximide (CH) and puromycin (PU), at each stage of the interphase in first cell cycle. The results indicated that both CAP and CH induced the chromosome fragments of dot type after the treatment in early S, late S or early G2 cells, but PU produced no chromosomal aberrations. These chromosome fragments seemed to be produced by a 1-hit event. On the other hand, S cells treated with CAP or CH markedly reduced the number of chromosomes in a cell. The chromosome reduction is likely due to the nondisjunction of chromosomes. Moreover, CH inhibited the protein synthesis as revealed by the incorporation of 3H-lysine, but CAP did not depress at the concentrations used. It was discussed that chromosome fragments are attributable to the chromosome nondisjunction.
The ultrastructural changes of the nuclear envelope from nuclei in the root cortex of Lepidium sativum L. during mitosis was analysed by means of freeze etching techniques and by series of ultrathin sections. It could be shown with the electron microscope that in contrast to the well known light microscopic fact of the “break-down” of nuclear envelope during late prophase nuclear double membranes are split into pieces. These, however, don't loose their structural characteristics (e.g. nuclear pores) during meta- and anaphase. The diameter of nuclear pores and their number per square micron of nuclear envelope is changed during single phases. It seems likely that the relative pore area per nuclear surface is constant (cf. Wunderlich 1969). The nuclear envelope of telophase nuclei consists of pore containing remnants of the parental nucleus and pore-free parts of the new incorporated ER membranes. This miscellaneous character of the nuclear envelope is lost during further stages of telophase. These results are discussed in respect to some autonomy of the nuclear envelope and under the aspect of the possible role of nuclear membrane as controlling the rate of DNA synthesis (Alfert and Das 1969).
Thirty-five smooth bromegrass clones from naturalized populations were analyzed for structural chromosomal aberrations which included unoriented chromosomes at M-1, laggards at AT-1 and AT-2 and micronuclei at dyad and quartet stages. Other chromosomal aberrations encountered, were translocation configurations, inversion bridges and physiological disturbances of chromosomes. The primary objective of this investigation was to examine the nature of chromo-somal aberrations and to determine their influence on fertility levels in naturalized populations, and to compare with the results reported for artificially grown populations, of Bromus inermis. Results indicated that structural chromosomal aberrations such as unoriented chromosomes, laggards and micronuclei occur in naturalized populations at much lower frequencies than those reported for artificially grown populations. The frequency of micronuclei at the quartet stage could be used as an index of structural chromosomal aberrations during earlier stages. A significant negative correlation between quartet micronuclei frequency and stainable pollen indicated that fertility levels in naturalized polyploid populations of smooth bromegrass are appreciably lowered by structural chromosomal aberrations. Physiological disturbances included prophase pycnosis, stickiness at M-1, split metaphase plates, interchromosomal adnations in dyads, asynchronous divisions, heteropycnotic nodules on quartet nuclei and pentad or hexad formation at quartet stages. These chromosomal anomalies as well as fragments, translocation configurations and bridges were present at such low frequencies that the data was not amenable to a statistical treatment. The preponderance of bivalent formation at diakinesis supports the contention that the species has undergone considerable diploidization from the auto-allooctoploid stage of evolution.
Pit connections, biconvex, equatorially constricted discs (0.3-0.7μ in diameter), develop between newly formed cortical and segment cells of Ceramium diaphanum. Biconvex, constricted forms represent early developmental stages of pit connections. Similar forms have been found in apices of Callithamnion roseum and Polysiphonia sp. As pit connections mature they increase mainly in width. Equatorial furrows become less pronounced. Flat, wide, lens-shaped forms consist of a granular material of high electron density. Current information on these structures suggests that their classification by Jungers is incorrect. Pit connections of red algae consist of a single body whose morphology varies with development.