Chromosome Clumping Research Articles

CYTOTAXONOMIC STUDIES IN CHRYSOTHAMNUS (ASTEREAE, COMPOSITAE)

The basic chromosome number for Chrysothamnus is x = 9 as determined by 234 original counts representing all species. Polyploidy is frequent only in C. viscidiflorus where diploids, tetraploids, and hexaploids are found. Pollen size in the genus is basically correlated with style length rather than ploidy level. Most aspects of meiosis appear normal except for the tendency for nucleolar fragmentation. To reduce chromosome clumping during meiosis, an ice‐water pretreatment was utilized. Karyotypes in Chrysothamnus reflect similar trends of specialization noted in chromosome structure for other Compositae. The taxa are predominantly self‐fertilized; however, one instance of interspecific hybridization is noted. Taxonomic significance of the chromosome numbers, karyotypes, and breeding system in Chrysothamnus is discussed.

Electron microscopic studies on rabbit ova: II. The penetrated tubal ovum

The nuclear and cytoplasmic changes that occur in the rabbit tubal ovum after penetration by the spermatozoon have been considered. At the completion of the second meiotic division, the nuclear changes begin with the reconstitution of a double envelope around individual chromosomes. This is followed by migration of the chromosomes toward the center of the cell, chromosome clumping, and formation of a female pronucleus. The cytoplasmic changes are characterized by reorganization of the ergastoplasmic reticulum, development of a hypertrophic Golgi apparatus, and the appearance of annulate lamellae. The significance of these morphological changes is considered and discussed.

Studies on Spontaneous and Induced Mutations

1. In spite of the many and varied reports on spontaneous mutations the factors responsible for their widespread occurrence in nature have not so far been clearly understood. Investigations carried out in the present study showed that decaying organic substances like compost, cowdung and oil cakes when present in high concentrations in the soil are capable of inducing mutations of different magnitudes. Chromosome changes induced by these substances and their possible role in the production of mutations in nature are discussed in this paper.2. High concentrations of compost, cowdung and oil cake in sand exert a distinctly harmful effect as regards germination and growth. Very high concentrations of bassia oil cake (1 oil cake: 5 sand) inhibited germination. Though germination was observed in fresh cowdung the plants did not survive. No such inhibition in germination was observed in compost unmixed with sand. Lower concentrations of these substances have been found to be beneficial.3. Cytological changes induced by compost, cowdung and oil cakes were almost similar. Breakage of chromosomes followed by reunion resutling in repatterning of chromosomes (translocation and inversion), chromosome doubling leading to polyploidy and spindle abnormalities resulting in the formation of aneuploid cells were commonly observed. Chromosome clumping, cytomixis, asynapsis, erosion of chromosomes etc. were some of the other abnormalities observed.4. Quantitative analysis of the data showing the frequencies of the different abnormalities in the different treatments showed that the frequency of abnormalities increases with an increase in the concentration of the substances in the sand.5. There is a gradual decrease in the percentage of aberrations with longer duration in compost, this relation being found in the pollen mother cells also. It is suggested that this decrease may possibly be due to the gradual fall in the content of nitrogen or other substances in compost causing these aberrations.6. Cytological changes induced by a few fertilizers like ammonium sulphate, ammonium nitrate, ammonium phosphate and potassium chloride were studied with a view to comparing their effects with those of the organic manures used for the study. Abnormalities in cell division induced in the root tip cells of onion following treatment with these chemical fertilizers were almost similar to these observed in treatments with organic manures like compost, cowdung and oil cakes. The results of the studies appear to show that nitrogen, phosphorus and potassium can act as mutagenic factors in compost. The differences exhibited by compost, bassia oil cake and cowdung might probably be due to the variation in the relative concentrations of nitrogen, phosphorus and potassium present in them.7. There is striking similarity between the aberrations induced by decaying organic substances like compost, cowdung and oil cakes and those reported as occurring spontaneously. It is suggested that decaying organic matter which is present in plant environment under natural conditions in varying concentrations, and those added as manures in agricultural practices, are responsible for some at least of such spontaneous mutations which play an important part in the evolution of species.

MORPHOLOGICAL AND CYTOLOGICAL EFFECTS OF DICAMBA ON WHEAT AND BARLEY

Dicamba (2-methoxy-3,6-dichlorobenzoic acid) applied to wheat and barley during periods of high meristematic activity disrupted normal growth and induced morphological and cytological aberrations. The intensity and locale of the morphological effects varied with the dosage and time of application. Under field conditions an application of 4 oz per acre before the 4-leaf stage caused gross malformation of the stems and leaves, reduced height, delayed maturity, and interfered with normal seed development in the main culms. Applied during the 4-leaf to 6-leaf stages this dosage interfered with tiller development and markedly reduced seed production in the main culms. Applied during the boot and early headed stages it largely prevented kernel development in both crops. Under lush conditions of the greenhouse, similar effects were induced by half this dosage. Doubling of the rate of application intensified and prolonged these effects to the extent that response differences due to growth stage were largely masked. Root tips of wheat and barley seedlings, germinated in different concentrations of dicamba, showed a sharp reduction in the numbers of dividing cells, viz., 133, 109, 97, 66, and 21 in concentrations of nil, 1, 5, 10, and 100 p.p.m., respectively. However, once initiated, mitosis appeared to proceed in a normal manner. At 10 p.p.m. and upwards, there was much evidence of chromosome clumping and the formation of multinucleate cells. Cell development and arrangement in the florets of treated plants was grossly disturbed.The response pattern of both crops resembled that induced by 2,4-D but the dosage of dicamba required was significantly less.

Delayed 'primary' effects in Chara vulgaris L. subjected to x-rays.

‘PRIMARY’ or ‘non-localized’ effects in the form of clumping of metaphase chromosomes or the sticking together of sister chromatids in cells that complete mitosis shortly after irradiation during the period when mitotic frequency is decreasing have already been described by numerous investigators.

The role of ribonucleoproteins in the production of mitotic abnormalities.

Immersion of growing roots of onion and lily in aerated solutions of ribonuclease affected their pattern of growth and altered the structure and mitotic distribution of the chromosomes. Action of the enzyme on meristematic cells caused enlargement of nucleoli, excessive contraction, stickiness, adhesion, and clumping of chromosomes, and production of aneuploid and polyploid chromosome complexes, tripolar and multipolar spindles, binucleate and multinucleate cells. Very few cases of chromosome fragmentation were observed.

Cytological conditions in root tip meristem after gross antagonism of phenylmercuric poisoning

1. 1. The dividing cells of onion root tips were protected by yeast extract, glutathione and cysteine in excess against PMOH 3.4 × 10 −5 M which alone caused clumping of chromosomes in an hour's exposure. Spindle inhibition was not eliminated, but in concentrations of PMOH and of PMN near 10 −5 M it was delayed or more rapidly overcome. The effect was similar to an 80 to 95 per cent reduction in the concentration of the mercurials. 2. 2. A day after antagonism of PMOH 3.4 × 10 −5 M with cysteine 8 × 10 −4 M for an hour, a majority of dividing cells showed mitotic abnormalities characteristic of narcotic concentrations of PMOH. A few showed arrest of metaphase chromosomes on the equator as produced by cysteine alone. 3. 3. Successful antagonism of lethal concentrations of PMN in prolonged exposure was accompanied by accumulation of blocked metaphases. Spindle formation was renewed after return to tap water. 4. 4. In all experiments, even when gross effects were practically eliminated by antagonism with thiols, radiomimetic effects (chromosome fragments and chromatin bridges) appeared in dividing cells after exposure. 5. 5. Effective concentrations of all antagonists by themselves caused mitotic and chromosomal abnormalities.

Cytohistology of the Reaction of Maize Seedlings to Colchicine

1. Seedlings of maize were treated with colchicine. Morphological abnormalities consisted of stunting of the seedling and swelling of the coleoptile node and of the root tip. 2. Sections of the root tip and plumule exhibit parallel mitotic aberrations-for example, multipolar spindles, clumping of chromosomes, multinucleate cells, and giant polyploid nuclei having varying degrees of lobing. These responses are especially prominent in the marginal meristems of leaf primordia, the epidermis and mesophyll of young leaves, and in both the plerome and periblem of root tips. 3. The massive promeristem of the plumule is relatively unresponsive; cell expansion in the calyptrogen appears to be inhibited.