Critical analysis of chromosomes at pachytene and later stages of microsporogenesis in six different species of Eu-Sorghum namely S. vulgare, S. durra, S, caudatum, S. roxburghii, S. sudanense and S. virgatum and their 15 F1 hybrids were made. The hybrids involving one wild and one cultivated species showed relatively higher proportion of chromosomal abnormalities than those involving either both cultivated or both wild species. Pachytene pairing was found to be complete and apparently normal in two S. sudanense×S. durra and S. caudatum×S. roxburghii hybrids. Pachytene analysis in remaining 13 hybrids revealed the presence of some minute, though cytologically detectable, structural differences such as terminal as well as interstitial non-paired regions, small duplications and terminal deletions, and differential segments between the parental species. In spite of the existence of these meiotic irregularities in some hybrids, the subsequent stages of meiosis were quite normal leading to good seed setting. Cytogenetical mechanisms underlying species differentiation in the genus are discussed.
The large seeded and small seeded varieties of Lens culinaris were given acute and chronic exposure of gamma radiations. Their chromosomal aberrations during microsporogenesis of M1 generation were compared. In the chronic treatment, the univalents, trivalents, tetravalents, laggards and fragments registered a decreasing trend with the increasing radiation dose. Whereas, all the aberrations except univalents were found to go on increasing with the total acute dose received. The univalents here showed a depression at the highest dose. The other aberrations viz. tetravalents, multivalents, cells with clumped configurations, bridges at the anaphase/telophase, unequal pollen grains, and pollen sterility were on the increase at the corresponding higher doses. This was common in both types of treatments. The physiological effects in the case of chronic treatments was mainly attributed to the existing differences from the plants treated with the acute radiations.
Culture tissues were established from hypocotyl segments of Vicia faba. Chromosomal analysis from initiation to 1 year old culture was done. Only numerically and structural varaition in chromosomes were found without any spindle disturbances. Another significant feature was the occurrence of new chromosome complement i.e. submedian type in this culture.
The structural diversity of interphase chromatin in many distantly related plant species is described. Heterochromatin, which is visualized by a new Giemsa banding technique remains attached to a specific point on the inner side of nuclear membrane and determines a species specific orientation of chromatin. It is suggested that heterochromatin is responsible for non random arrangement of chromatin, somatic association and structural diversity of chromatin arrangement at interphase.
The cell cycle kinetics of Allium cepa meristematic cells has been studied when BrdU was incorporated into DNA at different moments of the S period. When incorporation occurred late in the S period, no delay was observed in the total duration of the interphase, while a significant delay was detected when BrdU was incorporated into DNA during early and middle S, suggesting that a relation may exist in plant cells between time of exposure to BrdU and FdU and the conclusion of the interphase. Furthermore, the high resolution power obtained by the FPG technique after BrdU incorporation into DNA allowed us to calculate the approximate amount of late replicating DNA in the S period. The results indicate that DNA replication is specially active at the end of S.
The localization of the constitutive Heterochromatin in the salivary gland chromosomes of Orthocladius bipunctellus and Cryptochironomus fridmanae was established by the C and Q banding methods. “Dark knobs” connected with the nucleoli in the chromosomes were discovered in the karyotype of the species studied, Bright constant fluorescence and an intensive C banding were observed in the zones where these “dark knobs” were located. The results obtained confirm our assumption that this a specific kind of heterochromatin-AT rich and free of non histone proteins. Heterochromatin is distributed in different bands of the polytene chromosomes of both species. It is assumed that variability in fluorescence and intensity of C banding depend on the chromosome packing.
Ninety two meiotic anaphases were critically analysed for paracentric inversions in Crotalaria sericea. All the four possible types of configurations, resulting due to the involvement of various chromatids in cross over within the inverted region, which may or may not be accompanied by cross over between centromere and inverted region, were found in this species. This is probably the first report where all types of configurations due to paracentric inversion/inversions are found in one species. The paracentric inversion/inversions seem to involve a large segment of long arm of the chromosome/chromosomes. One is tempted to conclude that paracentric inversion may not have been firmly established in the species but may be at a stage of ‘floating inversions’.
The desynaptic plant showed univalents ranging from 0 to 13 at diakinesis and metaphase I. In triploid plant 36 per cent of the cells showed eight chromosomes separating to one pole at anaphase I. The morphology, cytology and sterility studies were conducted in all the trisomics isolated. All the primary trisomics showed 6II+1III or 7II+1I at diakinesis and metaphase I. The frequency of trivalents was reduced at metaphase I. The trivalent resumed in chain of 3, V-, Y-, frying pan, S-, J- and 4-shape configurations. Based on cytomorphological distinction, the 16 trisomics were grouped in five classes as bushy, awned, slender, dark green and tiny.
Male meiosis investigated in twelve species of Vicia revealed that all the three gametic numbers (n=5, 6, 7) reported so far, in the genus, were present. Majority of them showed regular occurrence of 5, 6, 7 bivalents at diakinesis and metaphase I. The univalents, observed in some species, never exceeded two in number. The chiasma distribution was generally random and their frequency in each bivalent was dependant on the chromosome length. However, in V. hybrida, due to localization of chiasmata at distal ends in 5 out of 6 bivalents, the chiasma number was never more than two per bivalent. Highest recombination index was in V. faba and lowest in V. hybrida and in the former the terminalization occured very late. The three size classes among bivalents in PMC complements of various species and even the position of centromeres in bivalents could be clearly earmarked. The species differed markedly in overall chromosome size and on this basis they could be divided into four major groups. The distribution of chromosomes at anaphase I was normal in all the species. It is concluded that the gametic numbers of 5 and 6 are derivatives of n=7. The variation in gametic numbers, localization of chiasmata, pericentric inversions, differential chromosome size in various species and gene mutations might have played a significant role in speciation in the genus.
The karyotypes of two Malaysian murids Hapalomys longicaudatus Blyth and Pithecheir melanurus parvus Kloss are reported. Both species have a diploid number of 2n=50 and large metacentric X and large subacrocentric Y chromosomes. The differences found in the autosomal elements may be attributed to pericentric inversions. These karyotypes are also compared with those of two closely related genera, Lenothrix and Chiropodomys. The karyological differences could not be readily explained in terms of simple chromosomal mechanisms.
The karyotype of Myotis pruinosus was presented for the first time (2n=44, FN=52). The odd karyotype was characterized by having a submetacentric pair (no. 1) and a large submetacentric X-chromosome. By comparison of the G- and C-banding patterns between this species and other Myotis species examined so far, it is clear that the submetacentric pair (no. 1) has developed by pericentric inversion from the standard metacentric, and the X-chromosome is due to the result of duplicated translocation on the short arm of the standard X-chromosome of Myotis species.
Roots of V. faba were treated with 5-AU (350ppm) and colchicine (0.025%) in various combinations. Tetraploid cells, induced by colchicine, were used as a subpopulation of marked cells with which to study the effect of 5-AU on G1 cells and to determine the relative rates of recovery, from the 5-AU induced block, of cells in different phases of the cell cycle. These aspects were followed in roots given 2, 18 or up to 26 hours in 5-AU: colchicine treatments were given either immediately before or after the 5-AU treatment. Cells exposed to 5-AU in the early part of interphase recovered more rapidly than those treated at the S-G2 transition. This recovery does not appear to be due to a stimulation of cells by colchicine, since treatments with colchicine after 5-AU did not speed up the recovery of the cells. Recovery appears to be a response of the whole meristem, not just of individual cells. This suggests some form of cell-cell interaction that results in the reversal of the 5-AU blockade.
Morphologically distinct plants were noted in M2 generation of G. hirsutum varieties Acala glandless, Empire glandless, MCU-5 glandless and Laxmi and one in G. barbadense var. Giza-45. Meiosis in these plants indicated that the PMCs contained (2n=3x=39) chromosomes. From the behaviour of 3x=39 chromosomes, it is suggested that the loss of 13 chromosomes in these plants is not only from A or D genome alone but few chromosomes from both the genomes. Splitting of spindles resulting in super-reduction might have caused triploidy in these plants. The pollen grains formed showed high size variation and low fertility. Pollen germination test indicated pollen sterility. Significant differences were observed in triploids for all morphological characters when compared with their parents which might be due to the deletion of thirteen chromosomes. Thus, these characters appeared to be governed by polygenes present in both A and D genomes.
Cannabis causes the dissolution of the chromatin substances of Allium cepa cells. We were able, in this present investigation, to pursue the process of chromatin dissolution by applying cannabis for long exposure periods. Exposure to cannabis for a long treatment time dissolved the chromatin material within the nuclei, leaving only the nuclear membrane bounding an empty area. It seems that the process of dissolution of the chromatin substance is irreversible. Micronuclei can be induced in long exposure time with cannabis. Micronuclei can be considered as a test of chromosomal damage. But in short exposure treatment cannabis has not the ability to affect the chromosome structure. As far as the nuclear membrane is concerned, there does not seem to be any difference between normal and treated cells. The only unusual feature which is frequently found is deep invaginations of the membrane into the nucleoplasm. These infoldings are responsible for the irregular outline of many nuclei observed in root tips treated with cannabis.
Cytoganetical investigations were carried out in some species of Ocimum. During the course of this investigation it was found that O. canum Sims and O. americanum Linn., which have long been considered as synonym, are two distinct species. The former has 2n=24 or its aneuploid form with 2n=26 chromosomes while the latter has 2n=72 chromosomes. It is suggested that O. americanum arose as a natural hybrid between the diploid O. canum (2n=24) and the tetraploid O. basilicum (2n=48) followed by doubling of chromosomes. An experimental evidence to support this hypothesis is provided by resynthesizing O. americanum from O. canum and O. basilicum. The interrelationship and evolutionary aspects of the species are also discussed.
Morphology of pachytene chromosomes was studied in Spanish (TMV-2) and Virginia (M-13) types of groundnut. All the 20 chromosomes could be identified individually from certain diagnostic characters in addition to their total lengths and arm ratios. A simple key has been proposed for classifying the different chromosomes to facilitate their easy identification. The ‘A’ chromosomes described earlier were found to correspond to a small chromosome that was completely heterochromatic. The ‘B’ chromosomes were traced to a bivalent with 2 large heterochromatic segments in the short arm. Chromosome morphology was more or less similar in both the varieties.
Treatment with actinomycin D has been found to block the meiotic development in a large proportion of pollen mother cells in Delphinium. In the treated plants, the anthers on squashing are found to show two kinds of cells-those showing the expected meiotic activity and the others which show a mitotic kind of division. The latter group of cells seem to have taken a mitotic course rather than the expected meiotic sequence. The drug has the effect of blocking the differentiation of premeiotic mitotic cells along the expected meiotic pathway. This effect of actinomycin D has been interpreted as due to the action of this chemical in inactivating certain gene loci, which are thought to be involved in a meiotic development of the cell. These loci may be controlling the synthesis of protein molecules, and possibly of the DNA fraction, which is believed to be involved in meiotic development. Thus, enzymes like DNA polymerase may be affected in their synthesis and so also the repair replication enzymes, which have a role in genetic recombination.
Three interspecific hybrids of Abelmoschus, viz., A. esculentus×A. tetraphyllus, A. esculentus×manihot and A. esculentus×A. manihot ssp. manihot, and their colchiploids were compared for stomatal length and frequency, frequency of stomatal chloroplasts and pollen diameter. Significant increase in stomatal length and frequency of stomatal chloroplasts and significant decrease in frequency of stomata per unit area were observed in polyploids as compared to the respective F1 hybrids with no overlapping. Frequency distribution for pollen diameter of the polyploids revealed a considerable overlapping though the differences were significant. Stomatal chloroplast count can be used as a reliable technique for identifying induced polyploids in Abelmoschus species.
Two out of sixty plants raised from the seeds treated with 0.2% NMU were found to be translocation and inversion heterozygotes respectively. The plant showing reciprocal translocation was characterized by the presence of a ring of four chromosomes and five bivalents in the PMCs. Rings were mostly of open type. The plant showing paracentric inversion had one bridge and one fragment at anaphase II in most of the PMCs. Such configuration could only result when two crossovers, one inside and one outside the inversion loop were formed. It is probably the first report where NMU has successfully been used to induce reciprocal translocation and paracentric inversion.
Vicia faba seedlings with attached cotyledons were cultured in 20% polyethylene glycol 6000 (PEG). Under this condition the mitotic index and incorporation of thymidine into DNA of root tip cells decreased during the first 8 hours of treatment and remained lower than the control for 40 to 56 hours. After this period of time both parameters increased to near the levels of the control indicating a self-recovery response. Seedlings transferred out of PEG after 24 hours of treatment showed a recovery in mitotic index and incorporation, but not to the control levels. Those transferred after 48 or 72 hours recovered fully. PEG-stressed seedlings lacking cotyledons did not exhibit self-recovery, indicating a possible cotyledon role in this phenomenon. Roots of stressed seedlings with attached cotyledons exhibited a drop in water potential, solute potential and turgor pressure demonstrating a close relationship between cell cycle responses and the water relations of root cells.
Somatic chromosome complements of pangolin, Manis pentadactyla have been studied from both male and female specimens collected from two widely separated states of India. The 2n number is 40 (neither 42 nor 36 as reported earlier) in both sexes and the NF (determined on the basis of the number of major autosomal arms) is 64. The X is a medium sized metacentric chromosome and the Y is a small C-band positive submetacentric element. Temporary satellite association between 3, out of 4 small satellite bearing chro-mosomes has been noticed during metaphase
Male meiosis was studied in 6 diploid, 3 tetraploid and I pentaploid Rosa species. Chromosome associations at diakinesis and irregularities at anaphase and telophase were scored. Pollen fertility was also determined. The diploids and one tetraploid, R. s. pimpinellifolia showed regular meiosis and high pollen fertility. The tetraploid hybrid species, R. macrantha showed fairly irregular meiosis with only about one third of pollen fertile. Highly irregular meiosis, with 6-7 bivalents and remaining univalents, was observed both in the tetraploid R. glauca and, pentaploid R. canina. Additionally these had a very high frequency of laggards resulting in formation of more than four pollen grains per PMC thereby drastically reducing the pollen fertility.
Male meiosis was studied in ten tetraploid (2n=28) garden roses. PMCs at diakinesis possessed univalents, bivalents and / or polyvalents in various frequencies. Certain combinations of chromosome associations were characteristic to each cultivar. The chiasma frequency varied from 14.77 to 18.04 per PMC and from 1.055 to 1.284 per bivalent. Various irregularities at first and second meiotic divisions resulted in 4 to 51% of PMCs with micronuclei formations which ultimately reduced the pollen fertility. Six out of ten cultivars were related and showed inheritance of various chromosome configurations. Three out of the six related cultivars carried an extra small B chromosome. This B was inherited for three generations and its presence was associated with higher univalent frequency per PMC and subsequently pollen sterility.
Cytological data with respect to 18 monocotyledonous ornamental taxa are presented. Sanseveria hahnii (2n=40) and Haworthia limifolia var. marlothiana (2n=28) were cytologically undocumented earlier. Earlier known chromosome counts are confirmed in the remaining taxa. Anew base number x=10 is suggested for Drimiopsis. Following karyotypes are established. Gasteria armstrongii: K(2n)=14=Ast2+Cst6+Hst2+Hsm2+Ism2 Haworthia fasciata: K(2n)=14=Cst6+Dst2+Hst4+Ist2 H. limifolia var. marlothiana: K(2n)=28=Dst*2+Dst10+Est4+Ist6+Ism2+Ism*2+Jst2 H. subulata: K(2n)=14=Cst8+Hst2+Ist4 Crinum asiaticum: K(2n)=22=Asm2+Bsm4+Csm*3+Cst5+Dm2+Dsm2+Esm2+Gm2 Zephyranthes candida: K(2n)=38=Cm2+Csm5+Dm4+Dsm4+Esm1+Est2+Fsm4+Fst2+Gsm12+Gst2 Z. grandiflora: K(2n)=50=Cm1+Dsm2+Esm10+Fst7+Gm2+Gsm9+Gst12+Hm2+Hsm3+Ism2 Z. sulphurea: K(2n)=48=Bm2+Cm2+Csm4+Dsm2+Dst3+Esm2+Est2+Fm2+Fsm4+Fst11+Gsm12+Hm2 Belamcanda chinensis: K(2n)=32=Gsm2+Gst*2+Hsm8+Im4+Ism8+Ist4+Jsm4 Karyotype analysis indicate chromosomal repatterning and/or hybrid nature of most of the taxa. Role of vegetative reproduction in the preservation of new genetic combinations is discussed particularly in the genera Haworthia and Zephyranthes. Accessory chromosomes are recorded in Anthurium acaule (2n=30+2-5B). Their origin is evident from the A's with which these pair during meiosis. Cytological distinctness of Sanseveria from other genera of Agavaceae is apparent.
In the genus Indigofera L., meiosis was studied in 24 collections belonging to 23 species and karyotypes with the help of root tip mitosis were examined in 26 collections belonging to 23 species. Three species, namely I. endecephylla, I. parodiana, and I. pilosa were tetraploid. Among diploid taxa, I. parviflora had 2n=14 and other remaining collections had 2n=16. Karyotype asymmetry was assessed following the two way classification of Stebbins (1971). I. glandulosa belonging to class 2B had the most asymmetric karyotype and was therefore considered most advanced. The length of individual chromosome ranged from 3.59μ to 1.10μ. The total chromosome length varied from 26.52μ to 11.35μ in diploid collections and was 35.81μ in the solitary tetraploid collection of I. endecephylla. The chromatin volumes and nuclear volumes were also worked out and had significant linear regression on total chromatin lengths. Five diploid species (I. asperifolia, I. brevidens, I. circinella, I. cryptantha, and I. neglecta) and one tetraploid species (I. parodiana) were cytologically examined for the first time and karyotypes were worked out in 13 species for the first time.
In comparison to chromosomal breakage (CB) studies, sister chromatid exchange (SCE) is considered a more sensitive indicator of chromosomal damage. The present study answers the question as to whether or not methylazoxymethanol acetate (MAM AC) exerts an effect on chromosomal breakage and sister chromatid exchange in short-term human leucocyte cultures derived from the same individuals. Only chromatid breaks were observed in a total 1168 metaphases. Statistical analyses of the data have indicated that there were no significant differences in the incidence of chromatid breaks when cultures treated with MAM AC were compared to control cultures (p>.2). However, an examination of 1020 metaphases derived from BrdU treated cultures from the same individuals revealed a significant increase in SCE with MAM AC exposure. Therefore, MAM AC has no effect on the incidence of CB, and SCE is a more sensitive indicator of chromosomal damage than CB is in this system.
Continuous light, with or without aeration, did not eliminate the midday peak of the mitotic index in root tips of diploid and triploid Allium triquetrum. However, when plants were grown in continuous darkness with aeration, the midday peak of the mitotic index was no longer evident. Aeration of the tap water in which the roots were grown increased the mitotic index in both 2X and 3X roots, indicating that a greater number of meristematic cells were dividing. Triploid root tips had a higher mitotic index than diploid root tips, partly because of an increase in the length of mitosis.
Predictions of associations among bridge and fragment elements (produced by the various crossover classes in cells heterozygous for paracentric inversions) differ for three models for the mechanism of chiasma maintenance until anaphase I. These models are: 1) that structural binding may be installed at the positions of crossover sites; 2) that telomeres may replicate or become effectively double very late (anaphase I); and 3) that generalized and persistent sister chromatid cohesiveness may exist. Results of detailed observations in maize microsporocytes from plants heterozygous for three different inversions are not readily explained by the first two models but are consistent with the third model.
The connection between mitochondria and microtubules was seen in growing cells of Micrasterias crux-melitensis. This connection was confirmed by examining serial sections with an electron microscope equipped with a sample tilting apparatus. A small hemispherical substance seened to mediate the connection of microtubules and mitochondria.
Electron-microscopical, histochemical and histophotometrical studies were given to the blue spherule present in the upper epidermal cells of rose petals exhibiting the bluing effect. The reults obtained are summarized below. 1. The observation with electron-microscope clearly demonstrated that three layers are distinguishable in the spherule, and that the parietal cytoplasmic layer which is lying along the cell wall takes the direction to the surface of the spherule running around it at the portion where the spherule is quite near to the cell wall. 2. When the intact spherules were treated with citric acid, EDTA and o-phenanthroline in the pH 3, 4 or 7, they retained the original blue color, but their blue color turned red by the reagents in pH 2 and 0.1 N hydrochloric acid (pH 1). 3. After the treatments of these reagents, iron was detected in the spherules showing blue color, but not in the spherule colored in red. 4. The complex staining of cyanin and ferric sulphate were given to the spherules decolored with 1% methanolic hydrochloric acid. The same staining features were obtained both in the Treatment 1 (decolored spherule→stained with cyanin→stained with ferric sulphate) and in the Treatment 2 (decolored spherule→stained with ferric sulphate→stained with cyanin.) 5. The absorption curves of the epidermal cells containing the blue spherule showed rather wide range of absorption from 470-680nm. 6. The relationship among anthocyanin, iron and the surface of the spherule is discussed.
Ultrastructural changes of the chloroplasts in the mesophyll cells of tomato plants which were exposed continuously to 2.0ppm ethylene up to 120hr were observed through the time course. At the same time, the effects of kinetin on the fine structure of chloroplasts were also examined. In the chloroplasts exposed to ethylene over 48hr, most of the normal membrane systems were decomposed and transformed into the macrograna. The chloroplasts exposed to ethylene for 48hr and then followed by 8 days water treatment had also macrograna in the stroma. However, the chloroplasts in the leaves undergoing natural senescence collapsed without the formation of macrograna. On the other hand, in the chloroplasts exposed to ethylene for 48hr and then followed by the incubation in kinetin solution (10mg/l) for 8 days, there were no formmtion of macrograna, and the thylakoid systems were kept with a little senescent symptom. To sum up, the ethylene exposure to tomato plants induces the formation of macrograna, plastoglobules and phytoferritin aggregates in the chloroplasts which are the significant characteristics of the chloroplast senescence. The kinetin treatment delays temporarily the chloro-plast senescence caused by ethylene exposure.
Chromosome pairing was studied in pollen mother cells (PMC) of the interspecific hybrids (2n=36) in Tagetes patula (2n=48) and T. erecta (2n=24). Among the 16 configurations of chromosomal pairing observed, the configuration with 12 bivalents plus 12 univalents was most frequently seen (30.56% of the PMC). A maximum of 15 bivalents was observed in a cell indicating some degree of intragenomal pairing in the hybrids. Trivalents and quadrivalent were present in 56.95% of the PMC, and 7.17% of the 36 chromosomes was involved in multivalent for-mation. In average, there were 10.97±0.20 univalents, 11.22±0.15 bivlants, 0.75±0.10 trivalent and 0.08±0.00 quadrivalent per cell. Laggards were very frequently seen (84.28% of the PMC). Pollen viability was 13.6% partly due to meiotic irregulatities. Seed fertility was very poor and physiological incompatibility may be considered a factor for the low fertility of the interspecific hybrids. The origin of T. patula is discussed.
An investigation is reported which was designed to determine if radiosensitivity of the G1-S and G2-M transitions of root meristem cells of Glycine max, Helianthus annuus, Pisum sativum and Vicia faba, is correlated with the number of cells in G1 and G2 in the stationary phase after 72 hrs of sucrose starvation or with their cellular DNA content. Stationary phase roots were irradiated with 137Cs gamma radiation at doses from 100R to 1000R and were compared on the basis of delay of entry into S and M, rate of S progression, total number of cells in S and M, and transition from G1 to M and G2 to M. 1) All species indicated a decrease in total cycling cells with increasing dose and a species correlation between the number of cells in G1 and G2 and radiosensitivity. 2) Most responses indicated the following order of radiosensitivity (least sensitive first)-H. annuus, G. max, P. sativum and V. faba. The sequence correlates best with stationary phase distribution and not with DNA amounts. 3) The relative sensitivity of each cycle phase was specific for each species. H. annuus, G. max and V. faba were equally sensitive in G1 and in G2. 4) An examination of irradiated G1 cells in each species indicated the absence of latent expression of damage for either G1-S or G2-M.
X-ray diffraction and freeze fracture of purified nucleohistones and nuclei of selected cell types establish a foundation for the nucleosome as a fundamental subunit of chromosomal structure. Glycerol-buffer (50% v/v) solutions at 4°C improved preservation of the giant salivary gland chromosome (Drosophila) within nuclei. Two results are achieved as observed with freeze fracture and transmission electron microscopy. 1. Where chromosomal bands and interbands unfold into nucleosomal sub-units and the nucleus is swollen. 2. Where chromosomal bands and interbands composed of nucleosomal subunits are preserved as condensed polytene chromosomes which completely fill the nucleus without detectable distortion.
Phenotypic plasticity and variations in chromosome numbers within the genera of the family Verbenaceae are known (Sharma and Mukhepadhyay 1963, Fedorov 1974). Fruits and seeds are formed sparsely off and on in most of the species of the genus Clerodendrum L. C. speciosum D' Ombrain has been considered to be a hybrid (Bailey 1949), but no cytological data have been adduced to support this contention. Whether a taxon is fully cytologically stable species or variety, heterozygous/homozygous, natural hybrid or comprised of translocated or inverted segments etc. can be clearly brought out by meiotic analysis (Stebbins 1971). Therefore, meiotic studies in commonly distributed nine species covering four genera viz. Clerodendrum L; Holmskioldia Retz; Petrea Houst, ex. Linn. and Lantana L. of the family Verbenaceae were carried out to determine their pure/hybrid nature, chromosomal behaviour during microsporogenesis and phylogenetic relationship. Meiotic pairing in six species of the genus Clerodendrum L. revealed lower frequencies of rod bivalents than ring bivalents. All most equal frequencies of rod and ring bivalents per nucleus in H. sanguinea Retz. and L. camara Linn. have been observed. In P. volubilis Jacq. Queens Wreath; rod and ring bivalents frequencies are 6.4 and 10.8 respectively. Not more than two chiasmata per bivalent have been recorded in any of the taxa investigated. Higher chiasma frequencies were seen in all the six species of Clerodendrum investigated than that of H. sanguinea, L. camara and P. volubilis. The meiotic behaviour of chromosomes stressed that each species has come to possess its own genotypic behaviour and cytological performance. No cytological configurations to indicate the hybrid nature of C. speciosum were detected. However, cryptic structural hybridity might have led to the formation of abortive pollen grains and seeds in C. speciosum.
The meristematic cells and dividing cells in Allium triquetrum root tips were counted and the mitotic index was calculated for diploid and triploid roots. The mitotic index was higher for 3X roots than for 2X roots (averages 11.82% and 10.7% respectively). The percentage of all cells that were dividing in also greater for 3X roots than for 2X roots (averages 11.97% and 10.71% respectively). There is no difference between 2X and 3X roots in the percentage of dividing cells in each phase of mitosis. It is concluded that there is a greater precentage of cells dividing in 3X root tips than in 2X root tips.
Effect of ageing of pollen grains on the behavior of the generative nucleus in Tradescantia paludosa has been studied. Pollen grains collected at 8 a. m. were allowed to stand for 7 hr at room temperature, and sown at 3 p. m. In both culture series conducted with the medium supplemented with one of either concentration of 10% or 20% sucrose, the elongation of pollen tubes was only slightly depressed by the ageing, but the mitotic activity was greatly depressed; namely, a great majority of nuclei remained in prophase. At the same time, the frequency of necrotic nuclei greatly increased, and at the end of 8hr cultivation, almost of all nuclei rushed into necrotic state before anaphase. Two different kinds of abnormal mitoses, i. e., unravelled twisted chromosomes and asynchronous condensation of chromosomal arms in the same nucleus, increased in the frequency.
C10 autotetraploid lines in two grain species of Amaranthus viz. A. caudatus and A. edulis were evaluated for their morphology and meiosis. Morphologically the C10 plants in both the species maintained the general gigantism in the determinate parts like leaves, stomata, pollen and seed as observed in C0 and C1. The meiosis was typically autoploid with quadrivalents, trivalents, bivalents and univalents. The mean quadrivalent frequency as observed at metaphase I varied from a minimum of 1.600 to maximum of 3.266 in A. caudatus while the respective figures in A. edulis were 1.400 and 2.33. The mean quadrivalent frequencies for C0 generation in the two species were 6.800±0.29 and 6.00±0.27, respectively. These figures represented statistically significant reduction over C0 and C1 data. The present results have been discussed in relation to similar or contradictory observations of earlier authors on the metaphase I associations in advanced generations of autotetraploids.
Triploids of Pennisetum typhoides (2n=14) were isolated in the progeny of the cross between autotetraploid and normal diploid. The meiotic instability in the triploid resulted in the recovery of aneuploids in their progeny. Aneuploids having chromosome number ranging from 2n=15 to 19 were observed. Among the aneuploids, trisomics (2n+1=15) were the most frequent types. Pennisetum typhoides though basically a diploid high tolerance of extrachromosome has been observed in this study.