The effect of water extract of Ammi magus on the mitosis of Vicia faba was studied in direct and recovery experiments. The results revealed that the extract caused a delay in the completion of the mitotic cycle. The interphase stages G1, S and G2 were not affected. The phophase and metaphase were the most influenced by the extract. The dominant abnormalities were: Stickiness, irregular prophase, bridges and with low frequcncy lagging, prophasemetaphase and despiralization.
A completely male sterile clone was identified in the germplasm and detailed meiosis showed it to be asynaptic. At pachytene all the chromosomes remained as univalents without any semblance to pairing. MI aslo showed 36 univalents in 97% of pollen mother cells. The bivalent like association in MI was as low as 0.03 per cell but the absence of pairing at pachytene and the lack of well defined x'mata suggested that they were only univalents lying closely together due to factors other than true pairing. The later stages were not well defined and univalents were noticed to divide. The scattering of chromosomes and irregular groupings resulted in polyads consequently all the pollen were sterile. The type of asynapsis noticed was ‘complete’. The presence of pollen sterility in all the plants of Ce-258 throughout the season ruled out environmental factors and suggested it was of genic nature.
The effect of gamma irradiation on chlorophyll metabolism was studied in leaves of Dolichos, Vigna and Phaseolus species, The dry seeds were exposed to 1.25KR, 2.5KR, 5.0KR, 10.0KR and 15.0KR doses of gamma irradiation and leaves from plants recovered from them as well as from control plants were tested for Chi. a, Chi. b and total chlorophyll contents. A comparison was made between chlorophyll contents of leaves from irradiated and non-irradiated populations. Chlorophyll content decreased at lower doses and incerased at higher doses in Dolichos lablab L., Vigna unguiculata L. and Phaseolus vulgaris L. But in D. biflorus and P. lunatus L. var. PI irradiation increased the chlorophyll content at all dose levels. In contrast the variety EC of P. lunatus L. recorded a decrease in chlorophyll content at all dose levels. The amount of chlorophyll b was more than that of chlorophyll a in all the plants investigated.
This paper deals with some morphological aspects of the nuclear apparatus in myolbasts and adult striated muscle cells if insects. The morphology of this nuclear cord-like apparatus is briefly described. The name of “polykaryonema” or “linear karyonema” is proposed to designate it.
The present communication deals with male meiosis and karyotypic analysis in five species of the two genera, Alisma and Sagittaria. The course of meiosis was investigated with great difficulty because of stickiness of chromosomes. Alisma plantago-aquatica and A. gramineum posssess n=7 chromosomes with 5 chromosome pairs belonging to median-submedian category and 2 pairs to terminal category, while A. lanceolatum is at the tetraploid level with n=13. Both the species of Sagittaria sagittifolia and S. guayanensis possess a haploid number of n=11 chromosomes of which only 1 chromosome is of the median category whereas the other 10 belong to subterminal category. Karyotype evolution in the different taxa is discussed.
The present communcation gives cytological data of four taxa covering the families Butomaceae and Hydrocharitaceae. Two cytotypes were noticed in Butomus umbellatus (2n=26, 39). While the basic karyotype in these two taxa was unaltered, there was distinct difference in the size of chromosomes. Polymorphism in respect of chromosome size was noticed in Hydrilla verticillata and Hydrocharis dubia in the populations inhabiting different lakes.
Three varieties of Malus Pumila, namely, Rikhal Saharanpuri, Kharoo and Acc. 1877 have 2n=51 and are therefore, triploids. Although not as good as diploids, triploids are certainly superior to tetraploids, in the quality of fruit. Data on chromosome pairing in triploid PMC's are indicative of intergenomal homology, which speaks of their auto- or segmental allotriploid nature. Despite triploidy, fruits of all three varieties bear varying number of seeds carrying well developed embryos. The nature of seed is being explored.
Fifteen species of Sansevieria have been studied cytologically, of which 11 are diploids, 1 tetraploid, 2 hexaploids and one aneuploid. The chromosome number of 4 species has been reported for the first time, together with intraspecific polyploidy in one species. The karyotype is characterised by the presence of small chromosomes, and are not amenable to detailed analysis. Meiosis in diploid taxa was regular with the formation of 20 bivalents. A natural triploid was located for the first time in a clone of a diploid species, and is autoploid in nature. In higher levels of ploidy, predominant bivalent formation was noted. The genus is based on x=20 and hybridisation coupled with polyploidy seems to have played an important role in the evolution of the genus. The polyploids have arisen principally through segmental alloploidy.
With an object of modifying the treatment conditions based on the concept of selection sieves, which may result in the higher mutagenic effectiveness and efficiency, barley seeds were treated with ethyl methanesulphonate (EMS) in various com-bination with non-toxic concentration of sodium azide (NaN3) and sodium arsenite (NaAsO2) as chemical modifiers. Treatments were carried out with dry, watersoaked and dried back seeds. Effects of these chemical modifiers in respect of pre-, post- and during treatment of EMS were also investigated considering the parameters, seedling injury, chromosomal aberrations, chlorophyll chimeras and sterility in M1 and chlorophyll deficient mutations as an index in M2. NaAsO2 did not induce chlorophyll mutations. However, NaN3 even in aqueous non-buffered solution induced chlorophyll mutations. As regards to their modifying action, although sodium azide and sodium arsenite both were used as common respiratory inhibitors, NaN3 was found to be most effective as a pre-treatment modifier in case of dry and dry-back seed treatments. Treatment of NaN3 soaked dried seeds with EMS synergistically increased the mutation frequencies but in general, combination treatments of NaN3 and EMS with soaked seeds were found to be highly deleterious. NaAsO2 has not been fonud to be effective as a pre-treatment modifier. It was very effective in during and post- EMS treatment combinations.
A series of aneuploids, starting from nullisomy (2n-2 i. e. 2n=18) to hexasomy (2n+4 i. e, 2n=24), has been isolated from a natural wild population of Coix gigantea Koen ex Roxb., a member of the tribe Maydeae of Poaceae. Among a total of 96 aneuploids isolated, the various chromosomal variants appeared as: 68 nullisomics, 13 monosomics, 12 trisomics and one each a tetrasomic, a pentasomic and a hexasomic. Higher polysomics-the pentasomic and the hexasomic-are reported for the first time in plants.
Published reports on chromosome complement of Plantgo lanceolata are at variance with respect to centromere position, proportion of various chromosome types, number of nucleolar chromosomes and position of secondary constriction. Consequently, the basi-karyotype for species has yet to be established. The present communication has made an attempt towards this direction. The number of nucleolar chromosomes have been authenticated by data on nucleolar number and the nucleolar attachment with two bivalents during meiotic prophase.
The development of sieve cells in the primary phloem of Pinus radiata needle traces was followed with the electron microscope. Sieve cell precursors have thin walls, a more or less spherical nucleus containing small evenly scattered masses of condensed chromatin, dense cytoplasm and several small vacuoles. Among the most obvious early changes are increase in cell size, condensation of chromatin, nuclear lobing, changes in the location and orientation of microtubules, modifications in the ER, increase in vacuolar size, increase in wall thickness, and sieve pore development. Later in the development of sieve cells and prior to their maturation the nucleus with greatly condensed chromatin and disrupted envelope assumes a necrotic appearance, and most of the cytoplasmic structures disappear with the exception of mitochondria, plastids and elements of ER. Callose and P-proteins are not seen at any stage in the development of sieve cells.
Differentiating sieve cells and neighbouring parenchymatous elements of Pinus radiata cotyledons contain a large number of bundles of microfilaments, the majority of which occur peripherally, Microfilament bundles are seen in association with the plasmalemma and several other cell structures. Sometimes a filament bundle was seen in association with more than one cell structure.
The nucleolar organizer of avian neurons is studied by means of a silver im-pregnation procedure. Its structure is compared to that of polytenic cells of diptera, insect ovocytes and other cellular types.
Of ten varieties of Trigonella foenum-graecum studied, all but one had usually one nucleolus in diplotene/diakinesis cells. In Sweden-B supernumerary nucleoli ranging in number from-2-10 were encountered in five plants out of the 16 investigated. The aberrant cells approached 100% in all. The nucleoli were of different sizes and seen to be attached to different bivalents. The presence of accessory nucleoli has been attributed to gene mutation/mutations which lead to disturbed genetic condition and a change in the regulatory system of the cell. Hybridity and environmental causes were eliminated. The difference in the size of the nucleoli has been explained on the basis of difference in the intensity of nucleolar forming power.
Meiotic studies of four species and three hybrid varieties of Mussaenda have been made. The chromosome number was found to be n=11 in all the cases. Meiosis was found to be normal in the four species The hybrids examined showed various abnormalities and high pollen sterility. Two species, M. glabrata and M. flava showed exceptional pollen development in which the vegetative nucleus breaks up and the nuclear fragments are included in “pollen buds” which are subsequently shed from the pollen.
Chiasma frequency per bivalent and per pollen mother cell of M1 plants raised from the seeds of Capsicum annuum treated with EMS, dES and HA was studied. There was a reduction in chaisma frequency in all the mutagenic treatments compared to their respective control. EMS caused a greater reduction in the frequency of chiasmata than dES and HA.
The nucleolus forming zones of the polytenic chromosomes of Drosophila hydei and Rhynchosciara americana are studied. It is postulated that the main nucleolus organizer of Drosophila hydei lies in the chromocenter. Those of Rhynchosciara americana are probably located in the four chromosomes, although the main organizer is the centromeric heterochromatin of the X.
Fifty eight species of the Compositae from Central India, which so far remained cytologically unexplored, have been worked out with new chromosome counts for the species of Eupatorium conyzoides (2n=40), Conyza leucantha (n=9), C. stricta (n=18), Blumea fistulosa (2n=30), B. lanceolaria (n=10), Helichrysum bracteatum (n=13), Laggera falcata (n=20), Wedelia urticaefolia (2n=72), Seneclo grahami (n=10), S. saxatilis (n=10), Goniocaulon glabrum (n=16), Tricholepis glaberrima (n=16) and T. radicans (n=16). Eupatorium conyzoides (4x), Blumea fzstulosa (3x) and Wedelia urticaefolia (4x) are the polyploid species in which meiosis is characterised by the presence of some multivalents. The frequency of polyploidy in the Central Indian Compositae is 20.3%, which is almost same in the annuals (21.1%) and perennials (20.0%).
Occurrence of cytomixis was detected in the M2 generation of a lax branching type mutant of Nigella sativa L. obtained through EMS treatment. Presence of cytomixis was restricted only in the prophase I cells of meiotic division. Transfer of nuclear materials from one PMC to the adjacent PMCs took place through cytoplasmic links and it occurred at random and in specific direction within the PMCs. Cytomixis resulted in the formation of aneuploid and polyploid PMCs. Hypo- and hyperploid meiocytes were observed in 19.87% cells. Multivalents were completely absent in the mutant plant which indicated that migration phenomenon has initiated after chromosome pairing in this material. Pollen sterility recorded in the mutant plant was 6.74%. Normal seed setting was not affected in the lax branching mutant. Aneuploids were detected among 0.65% individuals of the M3 population following selfing of the mutant, one of which was a trisomic. Phenotypically the trisomic plant was weak with slender stem and drooping lamina. The extra chromosome in the trisomic plant was present mostly as a univalent and rarely as trivalent. The plant was completely seed sterile due to unbalanced condition of the chromosomes in the zygote. The trisomic has arisen possibly as a chance occurrence through union of normal and aneuploid gametes, the latter being the consequences of cytomixis.
The meiotic events in post-metaphase I stages in the PMC of the hybrid L. auratum platyphyllum×L. henryi were observed. Restitution nuclei were produced in 75.6% of the cells at telophase t, followed by equational division. At ‘tetrad’ stage, 91.2% of the cells were diads mostly with one or a few micronuclei. Only 1.6% of the mature pollens germinated normally.
1. The nuclear behaviour and life-cycle in Absidia glauca (Mucorales) have been examined by a variety of microscopical techniques. 2. The uninucleate sporangiospores germinate to produce a coenocytic multinucleate mycelium. Vegetative nuclear division involves persistent nuclear envelope, asynchronous chromatid separation and lack of a metaphase plate. Sporangiospores formed inside the sporangium by a process of progressive cleavage, each protoplast containing a single nucleus. 3. Zygospores form after fusion by (+) and (-) gametangia on different mycelia. Nuclei fuse in pairs in the forming zygospore, but some nuclei remain haploid. Before zygospore dormancy a number of both haploid and diploid fusion nuclei degenerate. Remaining fusion nuclei are enlarged and probably in meiotic prophase before dormancy. Meiotic stages were not observed. 4. Zygospores did not germinate after dormancy by forming germ sporangia. Instead, hyphal development occurred inside a number of zygospores and a vegetative mycelium was produced. It is not known whether diploid nuclei divide meiotically or become haploid by successive chromosome loss during this process.