Chromosome number and karyotypes of the Misima subline of hyperdiploid Ehrlich tumor and three single cell clones derived from that subline were examined. The stemline cells of the Misima subline were characterized by the modal chromosome number of 44 including one A-chromosome (telocentric with secondary constriction), two B-chromosomes (large metacentrics), one Sa-chromosomes (chromosome with short arm) and two or three minutes. One small metacentric chromosome was remarkable, especially as it appeared after the 61 st transplant generation. The three clones had almost the same karyotypes as those of the stemline of the parental cell population. Karyotypes of the Misima subline and clones were compared with those of other authors and the differences between them were discussed.
The morphology and cytology of an accession of Coix collected from Madhya Pradesh has been studied in detail. Morphologically the plants are distinct from all the species so far on record. The plants invariably possess 32 chromosomes, a number new to the tribe, Maydeae. Karyotypic analysis shows a pronounced assymetry with regard to the ratio between the longest and the shortest chromosomes and the proportion of acrocentric chromosomes. The distinctive morphology supported by the different karyotype warrants a specific rank for this form of Coix. The possible mode of origin of this new form has been discussed in detail.
1. Among the progeny of 2n×4n crosses and crosses and selfings with respect to diploid plants of D. g. subsp. lustinica, four plants with conspicuous cytological abnormalities were found. Two of these plants differed morphologically also and they resembled in some respects to D. g. subsp. juncinella. 2. The cytological abnormalities included non-homologous associations of chromosomes, asynapsis, non-synchronization of chromosomal disjunction and cytokinesis, irregular chromosomal disjunction at both the meiotic divisions, formation of PMCs with more than 2n number of chromosomes and polymitosis. 3. These plants could have originated due to break-down of selfincompatibility and an inbreeding depression could be associated with their abnormalities. On inbreeding similar cytological abnormalities have been found in Alopecurus and Secale.
Seedling of Pisum sativum (var. Alaska) were cultured at 10°, 15°, 20°, and 25°C in the dark for several days. During this time length measurements were made on the root and the rate of growth determined. For three successive days samples were removed from each group and the mitotic index determined. The total number of cells in the terminal 2mm segment was estimated at day zero. Previous experiments, performed after the seedlings were maintained at a given temperature for three days, provided information concerning the minimum mitotic cycle time of root meristem cells (Van't Hof and Sparrow 1963b). These three sets of data provided the necessary information for investigating the relationship between the duration of the mitotic cycle, the rate of cell production and the rate of root growth at different temperatures. The analyses showed: 1) that the rate of root growth was primarily dependent on the rate of cell production which, in turn, was dependent on the duration of the mitotic cycle, 2) that the rates of root growth and cell production are functions of temperature differing in sensitivity to temperature change and in the maximum temperature limit, 3) that the rates of growth and cell production are interconvertible when the conversion factor for a given temperature is known and 4) the number of proliferating cells in the meristem can be calculated.
Meiotic behaviour of the chromosomes of a tetraploid has been studied with the following objectives in Artemisia vulgaris; 1. To understand the nature of polyploidy involved and causes of seed sterility. 2. The interrelationship of aberrant chromosome movement, spindle organisation and microsporocyte divisions and their overall relation to the changed meiotic rates. From the observations of abnormal meiotic behaviour source and limits of variability affecting fundamental processes of chromosome movement, reappointment and finally cell division have been studied. The material appears to be an autotetraploid. It has been concluded that it is the autopolyploidy that has contributed to meiotic instability because phenomena like nondisjunction and complement fractionation of chromosomes adding to their meiotic variability have been found. It is probable that the ployploids are untapped reservoirs of variability that can be drawn upon, to increase the meiotic instrability so as to induce variation at higher levels.
The ultrastructure of the chloroplasts in the leaves of Spinacia oleracea was examined. Three different appearances of the structure of the chloroplast were observed. In the first appearance, the grana seemed to be formed by sacs, the membranes of which were about 35Å thick. In the second appearance, the grana seemed to be formed by sacs, the membranes of which were very thin and hardly detectable. On the outside of the membrane small particles were observed. In the third appearance, the grana seemed to be formed by sacs with double membrane. The figures with the second appearance were assumed to be more significant than those with the other two appearances.
Root tip cells of Vicia faba, treated with tritiated 2-aminopurine (2AP), were found to be labeled in the nucleus, nucleolus and cytoplasm, thus indicating incorporation into DNA and RNA. In cells fixed immediately after treatment about two-thirds of the label was observed over the nucleus (including nucleolus), after one cell division this distribution was reversed, and after two cell division cycles the grain count was about the same over nucleus and cytoplasm. The reduction and changing distribution of average grain counts through two cell division cycles can be attributed to: 1) distribution of half the labeled DNA and RNA to each daughter cell, 2) shift of labeled RNA from nucleolus to cytoplasm, and 3) metabolic turnover of labeled cytoplasmic RNA. Characteristics of the range and variability in incorporation of 2AP can be seen in frequency distributions constructed from grain counts. All the curves were positively skewed and covered a wide range, which under these experimental conditions, extended from 0 to 40 counts over the nucleus of cells fixed immediately after 8 hr labeling.
1. Applying improved cytological techniques, the nuclear origin of the karyokinetic spindle and the presence of the spindle membrane are demonstrated in the mitosis of sea urchin eggs. 2. The biological significance of the spindle membrane is discussed free from any preconcieved ideas as described in current cytology text-books.
Cytogenetical studies of Pisum arvense, Lathyrus aphaca, L. sativus, Cyamopsis psoralioides, Glycine hispida, Vigna catjang and Dolichos biflorus was made. Morphology of somatic chromosomes was studied and idiograms were presented for all the species. Satellited pair of chromosomes were recorded in the first four species. Chromosomes with median, sub-median and sub-terminal primary constrictions were reported. The longest chromosome was observed in Lathyrus sativus (7.4μ) and the shortest in Glycine hispida (1.3μ). Meiotic studies in most of the species revealed regular chiasma formation. Chiasma frequency per bivalent was highest in Lathyrus aphaca (1.7) and lowest in Pisum arvense (1.3). Various meiotic anomalies were encountered. These included precocious separation of bivalents, stray bivalents, multivalents, delayed separation of bivalents, laggards and chromatin bridges. Multivalent formation was reported for the first time in Pisum arvense, Lathyrus aphaca, L. sativus, Cyamopsis psoralioides and Vigna catjang. Chromosome numbers already noted in different species were confirmed except in case of Dolichos biflorus. Pollen sterility was determined in all the cases, highest being 40% in Lathyrus sativus and lowest being 2% in Dolichos biflorus.