1. The present paper deals with the cytotaxonomical investigations of a terrestrial species of Oedogonium viz. O. pakistanense Islam and Sarma. 2. The detailed morphological characters of this material is very closely allied to O. pakistanense as reported by Islam and Sarma (1963) from Dacca and so this species has been reported for the first time from India. 3. The sequence of nuclear division in O. pakistanense follows the usual Oedogonialean pattern. 4. Original mitotic chromosomes count of n=17 is obtained for the first time in a terristrial species of Oedogonium viz. O. pakistanense Islam and Sarma. 5. Godward's (1948) iron-alum acetocarmine technique has been employed through out the present investigation for cytological studies.
Mesophyll protoplasts of Skimmia japonica leaves were isolated and cultured in a liquid medium. Changes occurring in the chloroplasts during isolation and culture of the protoplasts were followed by electron microscopy using the thin section and freeze-etching technique. During isolation protein crystals appeared in the chloroplasts. In cultured protoplasts a decrease in the number of thylakoids and an increase in the volume of the chloroplast stroma was detected. Upon longer incubation the number of the chloroplasts became reduced. In numerous chloroplasts lipid droplets accumulated and concentric thylakoid structures were formed. The most striking result was the appearance of some peculiar aggregates of membranes at the periphery of the chloroplasts. It is supposed that these structures constitute profiles of aggregated tubules of smooth endoplasmic reticulum. Frequently there exists a close proximity between these tubules and rough endoplasmic reticulum profiles which are in contact with the plasmalemma. The rough endoplasmic reticulum seems to be a chain between the tubules and the plasmalemma. Possible functional relationships between the described organelles and explanation of membrane proliferation at the periphery of the chloroplasts are discussed.
Degenerating changes after long durations of denervation have been studied in frog motor end-plate. During the 2nd month of denervation, the Schwann cell undergoes fissuration and the post-synaptic membrane displays the presence of furrows. The extent of the furrows in the post-synaptic membrane and fissuration of Schwann cell increases with increasing periods of denervation. The formation of furrows seem to be correlated with fissure formation in the Schwann cell cytoplasm. During the 4th month of denervation, at places, sequestration of postsynaptic fold from parent muscle occurs. The furrows in the postsynaptic membrane are eventually responsible for the sequestration of folds. In spite of the remarkable morphological changes at certain end-plates after long periods of denervation, the percentage of end-plates displaying spontaneous activity remains the same during this period (3-4 months) as after short periods of denervation (I2 months). This permits us to conclude that only at certain end-plate regions is the Schwann cell capable of producing acetylcholine responsible for miniature endplate potentials (min. e.p.p.s.) and this capacity is maintained until very long periods.
The mechanism of re-innervation depends on the period of denervation. After 2 1/2 months, when post-synaptic folds are intact but for the furrows, the reinner vation takes place at the former synaptic sites. The Schwann cell which is present in contact with the post-synaptic membrane till that time is withdrawn at the moment of reinnervation and the terminal bouton establishes contact with it. After 4 months of denervation, the post-synaptic sites are not always intact; at places there is sequestration and hence flattening of the folds. Thus, the reinnervation takes place, firstly, at old synaptic gutters where the synaptic sites are intact and secondly, by the formation of new neuromuscular junctions. The latter is marked by the specialisation of the parts of muscular membrane before the nerve is in contact with it. The process of reinnervation is gradual after short durations and is rapid after long durations. Similarly, the reappearance of the electric activity is gradual after short and abrupt after long durations. The miniature end-plate potentials (min. e.p.p.s.) in recently innervated muscle in both cases are characterised by their slow time course but normal in their frequency and distribution of the amplitudes. In case of some fibres, the min. e.p.p.s. had Gaussian as well as skewed amplitude distribution. This could be due to the unequal receptivity of the ACh or to the liberation of cholinesterases in variable amounts. The newly formed end-plates are capable of functionning before acquiring their normal morphological characters.
Karyotypes of 11 species and varieties of Salvia were studied. Chromosomes show certain remarkable peculiarities. Karyotypes are characterized by chromosomes of relatively small and uniform sizes. In the species S. farinacea (2n=18), chromosomes are the longest among all the species studied. Here two pairs of the longest chromosomes have secondary constrictions. Another pair of chromosomes are also long but without any secondary constriction. The remaining chromosomes are more or less of same size. The karyotype is strictly asymmetrical. The species S. grahamii (2n=22) has a relatively symmetrical karyotype. The longest chromosome pair has the secondary constriction. Three varieties of S. coccinea, all having 2n=22 chromosomes were studied. The karyotypes are symmetrical with only the longest pairs possessing the secondary constrictions. The species S. tiliifolia (2n=22) and S. leucantha (2n=22) also have a symmetrical karyotype with one pair of longest chromosomes having secondary constrictions. The species S. nemorosa (2n=14), S. horminum (2n=16) and S. reflexa (2n=20) show symmetrical karyotypes with median primary constrictions. In all the species, only the longest chromosome pairs have secondary constrictions. In the species S. officinalis (2n=14) an asymmetrical karyotype was found. One pair of chromosomes has secondary constrictions, but this is not the longest pair as noted in all other species. In a few species with very small chromosomes, only chromosome morphology was studied. It was not possible to locate the primary as well as the secondary constrictions. In the species S. splendens (2n=44), chromosomes are very small and are of equal sizes. In S. verbenacea (2n=54) 10 chromosomes are comparatively longer than the rests. Of the 10 chromosomes, 8 showed secondary constrictions. Here the karyotype is an asymmetrical one. In S. aegyptica (2n=26), all the chromosomes are more or less of same length with median primary constrictions. In S. pratensis (2n=16), chromosomes are more or less rod shaped. In the species S. hispanica (2n=12), lowest number of chromosomes was noted. Here also the chromosomes are rod like. In S. aethiopis (2n=22), 4 chromosomes are long and the rests are very short. Interrelationships among the species on the basis of chromosome morphology as well as evolution in karyotypes have been discussed in detail.
Longitudinal sections of testis tubules has been used to study the sequence of the prophase I in the male meiosis of grasshoppers of the genera Chortippus and Oedipoda. The sequence was determined and the presence of a diffuse stage found. An estimation of the duration of each phase in relation to the total duration of the prophase I has been made, namely synizesis 12.7%; zygotene, 16.7%; pachytene, 39.9%; diffuse stage, 8.2%; diplotene, 19.3%; and diakinesis 3.1%.
The karyotypes of seven Tilapia species were determined from fin biopsies. Five species (T. congica, T. guineensis, T. macrochir, T. galiaea and T. andersonii) have 2n=44 comprising two double-length stt pairs and 40 smaller chromosomes, mostly stt. T. mariae has 2n=42 and T. sparrmanii 2n=40 with respectively 1 and 2 double-length in pairs. Differences in arm ratio in the group of smaller chromosomes were also noted between most species.
A detailed cytological investigation of the endosperm in Datura fastuosa Linn. has revealed that the endosperm is basically triploid (3n=36) eventhough it becomes mixoploid by the appearance of higher ploid cells and some aneuploid cells in course of development. Endopolyploidy is brought about by endoreduplication, dispersion endomitosis, C-mitosis like division and also nuclear fusions. This is correlated with the vigorous growth of the endosperm and the fruit in general and hence may be considered as a positive adaptation.
Detailed morphological and karyological studies have been carried out on eight genera of Amaryllidaceae viz., Haemanthus multiflorus, Curculigo crassfolic, Zephyranthes tubispatha, Hippeastrum reticulatum Cyrtanthus mackenii, Crinum moorei, Alstroemeria japonica and Pancratium longjorum. Of these Haemanthus multiflorus, Curculigo crassifolia and Hippeastrum reticulatum were investigated meiotically also. Critical analysis shows, the karyotypes of Alstroemeria and Curculigo are distinctly different from one another and also from others and hence they need separation from others. There is gross homogenity in the karyotype among the other members especially in the nature of the nucleolus organising chromosomes. The bearing of morphological and cytological evidence in assessing the systematic position of these genera is discussed.
Morphology of the chromosome complements of the two N W Himalayan species is at variance with those from other places particularly in respect of centromeric position and the size and number of nucleolar organising regions. Whereas past work on F. roylei put the number of NOR's at two and eight per diploid set, present work has revealed occurrence of ten such regions. Again in F. imperialis present observations indicate the presence of four NOR's against two suggested by earliar workers. Support for the authenticity of present counts has been drawn from the number of nucleoli organized per nucleus. Structural variability in chromosomes particularly the ones bearing secondary constriction, appears to be the major source of evolution within the genus.
Nuclear area (NA), dry mass per unit area (DM/A), and nuclear dry mass (NDM) all declined considerably and comparably with fixation by FAA, 4% formaldehyde, 10% glacial acetic acid, or 50% ethanol. This suggests that nuclear dry mass measurements of fixed tissues may have meaning in a relative sense but not in an absolute sense. It also suggests a rapid degradation of nuclear dry mass with dying, since values obtained with fixation were similar to values obtained with fungal parasitism. The absolute values of DNA as determined by microphotometry following fixation and staining are therefore also suspected of being considerably lower than in the live condition.
Chromosome numbers and the reproductive biology of all the Canadian taxa of this tribe have been studied and their distribution maps are given. The chromosome number (n=7) for Isanthus brachiatus has been determined for the first time.
The development of plastids in tumor cells of Nicotiana-hybrids induced by the tobacco tumor virus (TTV) was studied by means of transmission electron microscopy and compared to uninfected controls. Proplastids and young chloroplasts in tumor cells contain intrathylakoidal inclusions. In contrast to controls the plastid development is delayed in young chloroplast stages. These are characterized by a poorly developed grana system and the formation of large starch aggregations. The ultrastructural changes in the intrathylakoidal inclusions were studied at the different stages of plastid development. Their possible functional role during plastid ontogeny is discussed.
Excised embryos (mature and immature) of five varieties of rice (Oryza sativa L.) were exposed to different levels of X-rays to assess the relative radiosensitivity response in vitro. The results indicated that: 1) germination was not affected in any of the varieties irrespective of X-ray doses and ages of the embryo, 2) the injurious effect of X-rays on germinating seedlings became visible from sixth day and seedling lethality could be noticed only from the seventh day onwards, 3) the LD50 value differed in different varieties, 4) early duration varieties were more sensitive to radiation than late, so also varieties with smaller embryos over those with larger ones, 5) the ‘day-neutral’ varieties were more resistant than ‘short-day’ types, 6) immature embryos were more sensitive to X-rays than matured ones, 7) a differential response to X-irradiation was noticed between varieties in vitro.
The effects of the herbicides monochloroacetic (MCA) and trichloroacetic (TCA) acids were studied on the meiosis and pollen viability of Vicia faba plants. The plants were sprayed at the seedling and flowering stages. The used concentration was 0.05mg/ml for the two agents. Both MCA and TCA affected a significant percentage of abnormal PMC's/plant. The most dominant types of abnormalities were: Lagging chromosomes, stickiness and fragmentation of the chromosomes, pentads at TII were observed after the treatments with TCA. Both agents showed a slight effect on pollen viability.
The action of MHQD on a meristematic root cell population of Allium sativum L. has been studied in order to investigate the possibility of using MHQD as a morphological labeller and to specify the advantages and disadvantages of the method. After a brief treatment, MHQD causes the immediate appearance of binucleate cells. These cells have normal kinetic parameters and there is no significant loss of synchronism between their two nuclei. This sample of labelled cell population goes synchronously throughout the cell cycle. Unlike caffeine, MHQD does not modify the mitosis duration nor the DNA synthesis ratio. Therefore, MHQD seems suitable as a morphological labeller, useful for the study of the action of various cell cycle inhibitors. Two examples of application of this method are given in order to outline its interest.
The khat extract showed a mitodepressive effect on the rate of cell division in Allium cepa root tips. This effect increased as the time of exposure increased, till it reached a maximum of complete inhibition of cell division after exposure. In the short treatment time of khat extract, the root tips showed a slight increase in the mitotic index after a period of recovery in water. The increase was greater with a more extended time of recovery. But after long treatment time (24 hours), 4 hours recovery was not enough to bring back the cell division. The longer the exposure, the longer the recovery time needed. The harmful effect of khat on the rate of cell division of Allium cepa root tips caused an imbalance in the frequencies of mitotic phases.
The mechanism of sex expression in D. deltoidea Wall. has been reported for the first time. The male has been shown to possess a pair of homomorphic sex chromosomes (ZZ) while the female have heteromorphic sex chromosomes (ZW). These results, in the light of earlier findings on the mechanisms of sex expression in the genus Dioscorea, suggest that different mechanisms may be operative in different species. The sex chromosomes in D. deltoidea Wall. are morphologically distinct from rest of the chromosomes and could be readily identified by an extended centromere which was submedian.
Extreme meiotic abnormalities in chromosome number and behaviour were found in three species of Salvia, e.g. S. farinacea, S. glutinosa and S. taraxacifolia. There were variation in the number of bivalent formation, and in anaphase separations, almost all types of abnormalities were recorded which were found to be associated with pollen grain sterility. The maximum number of chromosomal aberrations were found in S. farinacea which was directly correlated with the maximum percentage of pollen grain sterility. In the two other species, S. glutinosa and S. taraxacifolia, where chromosomal aberrations were low, pollen sterility was also low. Various causes assumed to be associated with these chromosomal abnormalities have been discussed in detail.
Chromosomes of the Indian spiny mouse (Mus platythrix) were observed by conventional, G-, C and Ag-NOR-staining methods. This species was characterized by 12 acrocentric autosome pairs in addition to acrocentric X and Y chromosomes. The comparison of G-banded chromosomes and chromosome length between the spiny mouse and the house mouse (M. musculus) had led the assumption that 8 autosome pairs (nos. 1 to 8) of the former species had been derived from the tandem fusion of two acrocentric pairs of the latter species. Pair nos. 9 to 12 and X and Y in the spiny mouse seemed to correspond in some autosome pairs and X and Y of of the house mouse. In this procedure, about 13 percent of the total chromosome length of the house mouse seemed to be lost to produce the new composites.
B chromosomes have been recorded in some plants of Petunia hybrida Vilm.. A single B chromosome was observed in the pollen mother cells and two in the seeds set by these plants. In all these plants during the male meiosis chromosomes formed multivalents indicating thereby that these are translocation heterozygotes also. Details of somatic and meiotic chromosomes in these plants are described.
The present investigation was carried out to study the cytological effects of adriamycin on root tip cells of Allium cepa. The roots of selected onion bulbs were placed in 3 different concentrations 0.1%, 1% and 10% of adriamycin solution for different durations, ranging from 3 hours to 24 hours. The treatments were so timed as to study the effects of the drug at specific stages in the mitotic cycle. The most important effect of the drug was the drastic lowering of the mitotic index. Interphasic cell death, nuclear lesions, nuclear dissolution, nuclear polymorphism and somatic reduction of chromosomes were also observed. Important abnormalities encountered at metaphase were C-metaphase, clumping, abnormal equatorial plate and delayed metakinesis. Chromatid bridges, sticky bridges, chromosome fragments, unequal distribution of chromosomes with paired chromatids, acute fragmentation leading to chromatin globules etc. were frequent in treated cells. Failure of cytokinesis resulting in multinucleate cells was also noticed. The present results suggest that adriamycin inhibits not only DNA synthesis but also protein synthesis, either directly or indirectly by its binding with DNA resulting in the prevention of its unwinding for transcription of spindle protein messengers. To arrest cell division, the best time of application appears to be the G1, just before the onset of DNA synthesis.
Electron microscopic observations were made on Cyanidium caldarium which is a thermophilic, acidophilic and unicellular alga. The organism, whose taxonomic position has been undetermined, contained a well defined nucleus and a large photosynthetic apparatus composed of a single envelope, single thylakoids closely resembling those of red algae, phycobilisomes and matrix, etc. The algal cell is enveloped by a thick cell wall made from at least three dense sublayers. Only one dumbbell shaped mitochondrion was located between nucleus and chloroplast. Other organelles, golgi bodies and microbodies etc. seen in eucaryotic cells were not observed in the algal cell in this study. However, the cytoplasm was occupied by a large number of dense ribosomes. From the standpoint of cell ultrastructure, C. caldarium may be a primitive rhodophyte, although from the characteristics of chloroplast fine structure, the alga shows a transitional form from blue green algae to red algae. From these observations, the taxonomic position of the present alga and the evolution of photosynthetic apparatus are discussed.
Chromosome number in Phaseolus vulgaris and Ph. coccineus is 2n=22. In F1 hybrids pairing is predominantly bivalent, the formation of occasional multiple figures indicating some structural differentiation. Multivalent formation is observed in the derived amphidiploid; frequency declines from C1-C5 with corresponding improvement in seed fertility and pollen stainability. Factors favouring homologous pairing are evidently selected. Meiosis and seed fertility in F2 and most F1 backcrosses are more or less normal except for the BC1 F1 (Ph. vulgaris×Ph. coccineus)×Ph. coccineus which had very low fertility. Introgression is possible reciprocally between the two species because the F1 interspecific hybrid, initially made on Ph. vulgaris can be backcrossed as pollen parent to both original parents used as seed parent. It is however very difficult to transfer two characters ‘cotyledon’ and ‘stigma’ positions between species which may be related to chromosomes structural differences. The fertility of the amphidiploid may be raised to the diploid level by recurrent selection.
Polyloidy was induced in the ornamental plant, Tagetus erecta (n=12) using 0.15 and 0.20 percent colchicine solution. Cytomorphological analysis of the colchiploids and diploid controls was made. It is seen that colchiploidy has effected significant enhancement of size of the capitulum and reduction in height of the plant. Both these characters add to the ornamental value of the plant.
The mode of meiosis in PMCs was studied in two members of Chionographis. C. japonica was found to have n=12 chromosomes, and C. japonica var. hisauchiana n=21 chromosomes. No localized kinetochore was observed in the chromosomes at various stages of meiosis. The bivalents at mid diakinesis showed various characteristic configurations, due to the presence of chiasma or chiasmata. Each bivalent at prometaphase I and metaphase I consisted of 2 homologous chromosomes connected end to end. Somewhat rectangular bivalents (in side view) were oriented axially with regard to the spindle at metaphase I. This mode of orientation of bivalents (axial orientation) differs from the one reported in some species of Luzula and some other organisms with holocentric chromosomes. Each pollen tetrad cell developed into a single mature pollen grain.