Vicia faba root tips were treated for two hours with several concentrations of the organophosphorus insecticides methyl parathion, dimethoate, oxydemeton methyl, azinphos methyl and phoxim, after one incroporation cycle with 5-bromodeoxyuridine (5-BrdUrd). Afterwards, the roots were exposed to a second replication cycle with 5-BrdUrd. The differential stain technique described by Tempelaar et al. (1982) with some modifications was used. The results showed that the two insecticides which are the most effective inducers of SCE are methyl parathion and phoxim. In no case was a concentration-response relationship observed. The treatments (except with dimethoate 0.5 ppm) produced SCE frequencies which differed significantly from those of the control.
The effect of 4 concentrations containing 4, 20, 100 and 500 ppm a.i. of the two fungicides dithane and denmart applied for 4 and 24 h. on mitotic activity and chromosomes in root meristems of Allium cepa has been investigated. Both compounds inhibited mitosis and resulted in the accumulation of metaphase configurations. High concentrations of dithane gave rise to lower prophase frequency, whereas those of denmart reduced the frequency of both anaphase and telophase. Both compounds exerted a weak C-mitotic activity, but induced chromosomal stickiness, breaks and bridges in a considerable proportion of dividing cells. Denmart also induced chromosome lagging, binucleated and multinucleated cells and micronuclei. In general dithane was more effective in inhibting mitosis, whereas denmart produced higher amount of chromosomal abnormalities than dithane. The significance of the cytogenetic effects of both fungicides is discussed.
We used root tips of annual Medicago disciformis DC. (2n=2x=16), perennial M. sativa L. ‘Lahontan’ (2n=4x=32), and plants of Lahontan that were regenerated from anther calluses to test various enzyme treatments for root tip chromosome preparation. These Medicago entries responded similarly to the types of enzymes and duration of treatment. Treatment with an enzyme solution (5.0% pectinase and 2.5% cellulase) for a duration of 60 to 90 minutes at 37°C gave the best results. The reliability of this treatment and the number of chromosome-countable cells was high. Distribution of cells and spreading of chromosomes in a cell on a focal plane was easily achieved. Treatment periods of less than 1 hour resulted in incomplete digestion. When the digestion time exceeded 90 minutes, many cells were too fragile to be processed. Either pectinase or cellulase alone failed to completely digest the roots, even after treatment for 5 hours. A solution comprised of 5% pectinase and 5% cellulase was so drastic that controlling the treatment time became very critical and difficult.
Cytology of six species belonging to three genera of the Papaveraceae is studied such as Papaver nudicaule (n=14), P. rhoeas (n=7), P. somniferum (n=11), Argemone mexicana (n=14), A. ochroleuca (n=14) and Eschscholtzia californica (n=6). Chromosome data show that a number of basic numbers exist in the family (x=5, 6, 7, 8, 9, 10, 11 and 19), of which x=6 and 7 are most frequent. The genera represented in the present study are based on x=7 and 11 in Papaver, x=7 in Argemone and x=6 in Eschscholtzia. The present polyploid species exhibited normal meiotic behaviour suggestive of allopolyploid nature. It is postulated that x=10 could be the earlier evolved basic constitution in the family from which the lower ones evolved by descending aneuploidy. It is also considered that the x=10 itself could be of secondary origin, arisen from a primary x=5. The disputed systematic relationships and affinities of the family are considered. The division of Bentham and Hooker's subfamily, Papavereae into splinter families, as done by Smith, is pointed out to be unnecessary.
Meiotic observations in this study indicate that the basic chromosome number in Sorghum bicolor is x=5 and that this species is a segmental allotetraploid. The wild and cultivated members of this species were crossed, producing at F2, an array of morphological types. One of the intervarietal hybrids showed complex multivalent associations with the attendant reduction in pollen viability indicating interchange heterozygosity. Based on the cytological and hybridization results a probable hybrid origin is proposed for Sorghum bicolor.
Almond and peach are cytologically very stable. All the variants of almond and the eleven varieties of peach explored for chromosome count during the investigation are diploid with 2n=16. Meiosis is regular in both the fruits except for occasional cases of nucleolar dispersion and cytomixis. In some varieties of peach namely, Peshawari, Chakli I and Gol II, microspores abort after they are released from the tetrad. Pollen viability is low in peaches and some varieties are totally male sterile. Meiosis is regular in the almond×peach hybrid; however, the Xta frequency is lower as compared to its parents.
Cytotaxonomical studies have been made in 17 species coming under 7 genera of South Indian Urticaceae. First record of chromosome number has been made in 1. Laportea terminalis, 2. Elatostemma lineolatum, 3. E. surculosum, 4. Pilea trinervia, 5. P. microphylla, 6. P. involucrata, 7. Pellionia repens, 8. Pouzolzia auriculata, 9. P. cymosa, 10. P. wightii, 11. P. bennettiana, 12. P. zeylanica, 13. Drougetia diffusa, and 14. Villebrunea integrifolia. The somatic chromosome number ranges from 18 to 50 among the species studied. n=10 may be the primary basic chromosome number and n=12 derived basic chromosome number. All the other numbers might have been produced by means of euploidy and aneuploidy. The karyotype analyses show that each and every species has a distinct karyotype. Therefore, karyotype alteration of chromosomes play important role in speciation along with aneuploidy and euploidy already discussed.
Cytotaxonomical studies have been made in 18 species coming under 6 genera of South Indian Capparidaceae, of which first record of chromosome number has been made in Cleome tenella, C. felina, C. aspera, Cadaba triphylla, Capparis brevispina, C. diversifolia, C. rotundifolia and C. divaricata. The basic chromosome number ranges from n=9 to n=80. The graph drawn on the frequency distribution of basic chromosome numbers shows a polymodel curve indicating thereby the evolution of species in many directions. The basic chromosome number may be n=7, from which species with n=9, n=10, n=11 and n=13 might have arisen by aneuploidy. The basic numbers n=16, n=17 and n=18 are secondarily balanced tetraploids by means of euploidy and aneuploidy. The basic numbers n=20, n=21 and n=22 may be secondarily balanced higher polyploids. The basic numbers n=49 and n=80 may be secondarily balanced allopolyploids which might have been evolved by hybridization of any two species followed by polyploidization. Therefore, autopolyploidy as well as allopolyploidy might have played important role in the the origin and evolution of the species of South Indian Capparidaceae.
A new Robertsonian translocation was found in several animals of the Blonde d'Aquitaine breed. The fused chromosome analysed by G and R banding results from the fusion of chromosomes 21 and 27. C-banding suggests that the fused chromosome is dicentric.
Mutagenecity, nutagenic effectiveness and efficiency of PS was compared to EI, EMS, sodium azide and X-rays. At biologically comparable doses selected on the basis of percentage inhibition in seedling growth PS excelled EI, sodium azide and X-rays but not EMS. It was 3-6 times more effective than EI, sodium azide and EMS and about 1.5 times more efficient than EI and X-rays. The efficiency of PS was, however, comparable to EMS and sodium azide.
The data generated during the present study reveals the impact of polyploidy and hybridity in three taxa of Argemone. The data highlights that the influence of polyploidy and hybridity is highly variable both with respect to morphological and biochemical parameters. The probable explanation for such plasticity has been discussed.
The effects of two organophosphorous pesticides, Ekalux EC 25 and Metasystox have been studied utilizing×235 a popular local variety of chilli. Seed germination and survival rate steadily decreased with increased dose of chemicals. They have also resulted in reduction of mean chiasmata per cell and induced clastogenic changes such as stickiness of chromosomes, formation of univalents, laggards, bridges and micronuclei in different stages of meiosis. From these studies it can be concluded that indiscriminate use of chemicals effect normal plant growth and resulted in reduction of yield.
The effects of two fungicides, Bavistin and Deltan were studied in chilli (Capsicum annuum L. var. x235). Both seed germination and seedling survival were effected with an increase in concentration. The mean chiasma frequency per cell was decreased with the increased concentration of treatments. Critical analysis of PMCs of treated plants revealed chromosomal aberrations including univalents and multivalents, stickiness and non-orientation of chromosomes at metaphase I, whereas chromatin bridges and laggards were observed at anaphase. The cytotoxic/chromotoxic effects have resulted in pollen sterility which ultimately decreased the yield. From these studies it can be confirmed that the low concentrations of the chemicals will only show favourable effects without any meiotic irregularities and the use of these chemicals during flowering stages should be avoided.
Cytomorphology of interspecific hybrids of Musa acuminata×M. rubra showed 2n=33 chromosomes. The hybrid had intermediate morphological characters. The occurrence of triploids in diploid×diploid cross suggested formation of unreduced female gametes in M. acuminata. The absence of unreduced male gamete formation in the same indicated differences in male and female gametogenesis in same species. Formation of 11 bivalents per PMC in hybrids apparently suggests complete pairing of all M. acuminata chromosomes and lack of homology with M. rubra chromosomes.
Behaviour of sex chromosomes and autosomes during meiosis have been studied. Meiosis was found to be normal. However, chromsomal aberrations were observed in a small number of pollen mother cells. Palynological studies indicated that the presence of prolate, 3-colpale, reticulate and clearly differentiated sexine and nexine pollen grains in the materials. Nine spots for phenolic compounds in leaves of both male and female plants were observed by thin layer chromatographic method. Delay in germination time, decrease in germination and seedling height and increase in morphological abnormalities with increase in X-ray doses and colchicine concentrations have been recorded. X-ray induced chromosomal aberrations in root tip cells increased with increase in X-ray doses. Cells with 3n, 4n and more than 4n chromosomes could be produced after treatment with colchicine. With increase in colochicine concentrations there was increase in cells with polyploid chromosome number. Induced chromosomal aberrations or polyploidy are not the direct cause for aberrant plant growth. It may be due to some factors associated with non heritable physiological disturbances, the exact role of which has not beeen definitely established.
L'étude du comportement méïotique de clones dipïoides et polyploïdes du pommier cultivé (Malus×domestica Borkh.) a été réalisée sur cellules-mères de grains de pollen. L'analyse de plaques métaphasiques conduit aux formules d'associations chromosomiques suivantes: 10 II droits et 7 II en anneau, 5, 35 I+7, 3 II+10, 37 III et 2, 23 I+20, 23 II+2, 69 III+4, 31 IV par cellule respectivement pour les diploïides, triploïdes et le clone tétraploïde. Au cours de ce travail, la cytomixie a été observée entre cellules-mères de grains de pollen chez tous les clones étudiés avec une fréquence variable et quel que soit le niveau de polïdie; ce phénomène a été principalement rencontré aux stades prophase I, interphase, prophase II et télophase II. L'observation chez les triploïdes d'un nombre total d'associations (somme des bivalents et trivalents) supérieur à 17 et chez les triploïdes et le tétraploïde d'une fréquence d'univalents inférieure à celle des trivalents, traduit l'existence d'associations intragénomiques. Nous avons observé seulement des bivalents chez les diploïdes, pas d'association de plus de 3 chromosomes et 4 chromosomes chez les triploïdes et le tétraploïde respectivement. Le pommier dont on admet une origine polyploïde, est vraisemblablement un polyploïde disomique si l'on considère les études diverses réalisées en cytologie, génétique, électrophorèse d'isozymes, morphologie et chimiotaxonomie.
Five meiotic abnormality types have been discovered in the apple clone ‘R1-23’ (2n=2x=34) known for its faculty to produce an important proportion of triploid seedlings after selfpollination. All these types of meiotic abnormalities can lead to the formation of dyads orof triads, and generate in this way non-reduced male gametes (2n). The types 1, 2 and 3 aretheoretically equivalent to the “SDR” (Second Division Restitution) mechanism and the types 4 and 5 correspond to “FDR” (First Division Restitution) mechanism. These non-reduced gamete production phenomena could be exploited in genetic breeding programmes after confirmation of the detected mechanisms and precision of inheritance of the meiotic abnormalities.
The meiotic behaviour and fertility of the six monosomic H. muticus plants with 2n-1=27 chromosomes isolated from populations raised from seeds treated with higher doses (70 kR, 80 kR, 90 kR and 100 kR) of gamma rays were studied. One of the plants mostly showed thirteen bivalents and one univalent at diakinesis/metaphase I as a result of loss of one normal chromosome was identified as primary monosomic. The remaining five plants were tertiary monosomics lacking interchanged chromosome and thus mainly exhibited twelve bivalents and a chain trivalent at diakinesis/metaphase I. All the monosomics showed a wide variations in chromosome distribution at anaphase I and anaphase II. The pollen fertility of monosomics was highly variable, stainable pollen ranged from 16.66% to 48.03%. Hand pollination with normal diploid pollen resulted in low seed set in three tertiary monosomics only.
Microsporogenesis in the two diploid clones of C. speciosus was studied in detail. The absence of cytokinesis detected in some of the dyads at the close of the second meiotic division was the mechanism producing 2n pollen in both the diploids. The distinct variation in n and 2n pollen size indicated the possibility of its use as a reliable criterion for estimating the frequency of 2n pollen in large populations. In addition to the normally expected diploids, certain triploid and tetraploid genotypes were identified in the selfed progenies of both the diploids which confirmed the occurrence of functional 2n gametes in their parental diploid clones. The present study suggested that sexual polyploidization involving the function of 2n gametes might have played an important role in the origin of naturally occurring intraspecific chromosomal races of C. speciosus.
Cytomixis was recorded during microsporogenesis in Papaver dubium L., a member of the family Papaveraceae. The phenomenon was observed in all the stages of meiosis. Further, it was found that not only the frequency of cytomixis but the amount of chromatin transferred reduced with the advancement of meiosis. The pollen fertility was found to be affected by this phenomenon and it seems that some other factors like precocious separation and irregular distribution of chromosomes might have also contributed towards the pollen sterility. A few large sized cells containing double or more than double chromatin and cells with increased or decreased chromosome number were observed. The possible role of cytomixis in the production of aneuploids as well as polyploids is suggested.
A case of spontaneous paracentric inversion heterozygosity has been reported in Papaver dubium L. for the first time. The chromosome number was found to be 2n=14. The dicentric bridges and/or acentric fragments were observed at anaphase and telophase in both first and second meiotic divisions. Persistence of anaphase I bridge upto telophase II was also noticed in some of the PMCs. The frequencies of the various meiotic configurations and an analysis of the cytological behaviour of dicentric bridges and acentric fragments are reported and discussed.
The present paper deals with the chromosomes of 10 species of weevils belonging to the sub-family Eremninae. But for Hypomeces squamosus and Phytoscaphus tenuirostris, all of them carry a diploid number of 22. The Xyp type of sex mechanism is apparent in the males of these insects. The karyotypic differences can be ascribed to the involvement of inversions and translocations etc.
Effects of vitamin C and vitamin A were reported on the damaged bone marrow chromosomes and sister chromatid exchange studies on mice induced by both metanil yellow and zinc chioride. The results indicate that the damage is not repaired fully either naturally or by the prolonged treatment of vitamin A or vitamin C. Thus the vitamins cannot exhibit their antagonistic properties when the damage has already taken place.
In the present study an endeavour has been made to assay the mutagenicity of an organophosphorus pesticide, monocrotophos (Nuvacron) in mouse cytogenetic test system. Cytogenetic assays like somatic chromosome aberration, micronucleus test and sperm shape abnormalities have been done. Different doses (5, 2.5 and 1.25 mg/kg), different exposure times (6, 24, 48 and 120 hours) and different routes (i.p., p.o. and sc) of administration have been employed. The effects are mostly dose, time and route dependent. Comparision of acute and chronic treatments revealed that the chemical has no cumulative effect. Relative sensitivity of cytogenetic assays has been found to be as sperm shape abnormality>chromosome aberration>micronucleus. Monocrotophos has been found to be mutagenic in the present test system.