Karyotype studies including determination of somatic chromosome number, total chromosome length and volume, 4C DNA content and INV were carried out in 6 species of Melocactusof the family Cactaceae. Somatic chromosome numbers 2n=22 in M. albicephalus, M douradaensis and M lensselinkianus and 2n=44 in M borhidii, M bredorooanus and M. ernestii were recorded for the first time. Significant interspecific variations in nuclear DNA amount were noted. The 4C DNA content varied in the diploid species from 21.95 pg in M. douradaensis to 24.31 pg in M lensselinkianus and in the polyploid species from 35.76 pg. M ernestii to 39.21 pg in M borhidii. The correlation coefficient studied showed that the chromosome volume, nuclear DNA content and INVwere positively correlated. No interdependency was found between average 4C DNA content and average chromosome length. The structural alterations in the chromosomes as well as less or addition of highly repetitive sequences in the genome showed variations in nuclear DNA at interspecific level indicating a macro-change of nuclear material during evolution.

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The permanent translocation heterozygote, Rhoeo spathacea shows a characteristic ring of all chromosomes at metaphase-I of male meiosis. Elimination of bivalent formation completely due to extreme heterozygosity poses a special problem for reductional division at meiosis-I where the maternal and the paternal sets need to be separated to different poles. Unlike bivalent meiosis, the functions of SC formation, pairing and recombination required for reductional segregation have to be fulfilled by only telomeres which are the only areas of contact among the chromosomes in the ring. The participation of telomeres in these events assumes significance in view of the balanced lethal gene system imposed by translocation heterozygosity, and the particular requirement that only alternate chromosomes segregated to the same pole results in fertile pollen. This paper throws some light on the telomere functions in R. spathacea in the light of our present understanding of telomere biology. The prospects of using R. spathacea as a model organism to dissect molecular aspects of several telomere related functions are also discussed.

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The analysis of the nucleolar organizer regions (NORs) in 4 Astyanax scabripinnis populations collected in the Yukatan stream (population A), Ligeiro stream (population B), Sarandi river (population C) and Água do Rancho river (population D) indicated the existence of inter-and intrapopulation variations in the number of NORs. The present study also showed a probable mechanism of preferential activation of nucleolar chromosomes, suggesting the presence of main activators as well as different activation patterns in each population. In population A, the large metacentric chromosome was the main nucleolar organizer occurring in about 67% of the cells analyzed, with this population showing the most characteristic NOR pattern compared to the other populations. In populations B, C and D, the main nucleolar organizer chromosomes were a large acrocentric chromosome (65%), a large submetacentric (70%) and a medium-sized submetacentric (71%), respectively.

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Evaluation of cytological stability has been made for R₁ and R₂ generations of anther derived doubled haploid wheat plants developed either spontaneously or in response to the addition of 100 mg/l or 1000 mg/l colchicine to induction media for a duration of 1, 3 and 5 days. Determined abnormalities in meiotic behaviour in chromosomal structure and number offered a confirmation for the role of culture conditions in generating gametoclonal variations in regenerated plants. Frequent failure of pairing, occurrence of chromosomal translocations and breaks in addition to aneuploidy were detectable in regenerated DH-plants but not in their parental anther donor control. Interpretations of origin and possible effects of detected types of gametoclonal variations in relation to potential value of anther culture technique has been proposed and discussed. Colchicine treatment had not affected the degree of cytological instability, since no significant differences were found between spontaneously arisen doubled haploids and those developed after treatments by two colchicine concentrations and three durations. The importance of closely monitoring regenerants of anther culture through a cytological evaluation for a safe and effective application in breeding programs is stressed.

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Meiotic behaviour of intergeneric hybrid between Cajanus cajan and Vigna mungo isreported for the first time. A majority of the meiocytes had normal meiosis but the frequency of ring bivalents was low. In some, univalents, trivalents, quadrivalents, unequal chromosome distribution and laggards were also observed. The hybrid showed very high pollen and seed sterility, which was attributed to both genic causes and abnormal chromosome behaviour. Formation of bivalents in high frequency suggested that the genomes of C. cajan and V mungo might be similar and gene exchange is possible.

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Peganum harmala extract caused an increase in mitotic index of Zea mays treated cells with increasing the time of treatment in all cases. Depression of cell division in these cells increase with increasing the concentration of the extract in almost all treatments, however, roots treated with the highest concentration showed decreased in their mitotic index. Harmala extract at 100% concentration induced a variety of cytogenetic variants of which ten classes were observed. These include abnormalities in chromosomal organization (distinct chromatid separation, visible chromatids, despiralization, C-bands, ring chromosomes) and nuclear organization (laggard chromosomes, anaphases with bridges, micro and multi nuclei, C-metaphase, polar metaphase). The frequency of abnormalities are significantly higher than controls in all treatments studied. These results suggest that harmala can act at many levels of organization and cause a wide range of abnormalities involving all the stages of mitosis in Zea mays root tips.

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To examine whether cytoplasmic rRNA are present at high density in the cytoplasm of generative and sperm cells (generative/sperm cells) in pollen grains of various plant species, in situ hybridization of 18S/25S rRNA was performed in thin sections of samples embedded in Technovit 7100 resin. The five plant species studied were Lilium longiflorum, Pharbitis nil, Silene latifolia, Pelargonium zonale and Plumbago auriculata. The timing and mode of pollen mitosis II (PM II) and the distribution of organelle nucleoids in generative/sperm cells differ in these species. In situ hybridization revealed that the density of rRNA was the same as or higher in generative/sperm cells than in vegetative cells, suggesting that the presence of rRNA in the generative/sperm cells at high density may be a general characteristic of mature pollen grains of various plant species.

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Meiosis in two species of Magnolia from South Indian, namely M. obovata and M. liliflora, has been studied. Meiosis in the former was abnormal due to formation of multivalents (penta-, quadri-and trivalent) along with bivalents and univalents together making up a count of 2n=95, while meiosis in the latter was normal with regular formation of 95 bivalents (2n=190). The findings show that the present materials of the two species are new polyploid cytotypes, M obovata 5x and M liliflora 10x on x=19. The n=95 reported here in M liliflora is the highest chromosome number known in the Magnoliaceae. On the speculation that the x=19 in the Magnoliaceae could be a derived one of tertiary origin, representing a 'paleo 6x' state, the present cytotypes of M obovata and M. liliflora may be reckoned as representing very high 'paleopolyploids'-15x and 30x respectively.

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Cytogenetic analysis on two lots of maize genotypes consisting of inbred lines, singlecross hybrids and double-cross hybrids grown in the South and Center West Regions of Brazil revealed the occurrence of spontaneous mixoploidy in the anthers of some plants. In the South Region the anthers showed only diploid and tetraploid cells, with the tetraploid ones presenting nuclear fusion. In the genotypes grown in the Center West Region the anthers showed a mixture of diploid, tetraploid, hexaploid and octaploid cells. In addition to nuclear fusion, some cells of these genotypes presented just cytoplasm fusion, with the nuclei remaining individualized. The percentage of poly ploid cells ranged from 1.0 to 47.6. The probable origin of the phenomenon and its implications in maize breeding are discussed.

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Chromosome studies and in situ estimation of nuclear DNA content were carriedout in two different cultivar of Z. officinale Rosc. Somatic chromosome number 2n=22 was found to be constant in both the cultivars. Karyomorphological analysis indicated high heterogenity. DNA content of these two cultivars were highly varied and a correlation could be obtained between the amount of 4C DNA and the total chromosome length. Average packing ratio was workedout from which the relation between the 4C nuclear DNA content and the total chromosome length were established.

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The C-banding pattern and Ag-NORs in the karyotpye of Bembidion lampros and Bembidion properans are presented. The results indicate that in chromosomes of the examined species the constitutive heterochromatin is located in the proximity of the centromeres. In B. properans the paracentromeric C-bands are similar in size. In B. lampros a large heterochromatin segment occurs on the 1st pair of autosomes and on the X chromosome whereas the other autosomes have shorter paracentromeric C-positive blocks but all nearly the same size. In mitotic stages, from the prophase to the prometaphase stage one silver dot on the end of two autosomes is visible. In prophase I (to diakinesis) one active NOR is observed.

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The karyotypes of seven South American species of Vernonia were analyzed in detail. First chromosome count are reported for V. amplexicaulis (2n=34=24m+10sm), V. ferruginea (2n= 34=20m+14sm), V. pinguis (2n=68=42m+26sm) and V. squamulosa (2n=34=20m+2m-sm+ 12sm). Furthermore, the chromosome numbers of V. chamaedrys (2n=34=22m+12sm), V. fulta (2n=34=24m+ 10sm) and V. nudiflora (2n=34=24m+ lOsm) are also confirmed. The seven species showed similar karyotype symmetry, chromosome size and satellite position, which would support a close relationship among them. Chromosomal data available for the genus and the results obtained here suggests that species with pyramidal or thyrsoid inflorescence have x=17, while entities with scorpioid or seriate inflorescence possess mainly basic numbers x=16, x=15 or x=14.

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Aldrovanda vesiculosa L., Dionaea muscipula Ellis, 20 species of Drosera L. and Drosophyllum lusitanicum Link. were investigated for a metaphase chromosome analysis by using the sequentially fluorescent CMA and DAPI staining methods. Aldrovanda vesiculosa and the Drosera species showed numerous small-sized chromosomes and some middle-sized chromosomes with no primary constriction. Dionaea muscipula had the middle-sized chromosomes with the localized centromeres and CMA-negative and DAPI-positive pericentric bands. Drosophyllum lusitanicum displayed quite large-sized chromosomes with well-defined localized-centromeres. Computer-aided measurements of metaphase chromosomes stained with CMA and DAPI showed that Aldrovanda vesiculosa and the Drosera species displayed the common features such as localization of CMA-positive and DAPI-negative satellites and non-staining region.

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The present investigation deals with the effects of γ-radiation (5-500 Gy) and growth hormones (IAA, GA and kinetin, 10, 25 and 50 ppm) on pollen germination and pollen tube elongation in P. kesiya Royle ex Gord. The effects of combination treatments of γ-rays (500 Gy) and 10 and 50 ppm of growth hormones (IAA, GA and kinetin) were also investigated to find out if radiation effects could be modified by growth hormones. The study revealed that 7.5-40 Gy γ-rays stimulated pollen germination and tube growth, but radiation doses 50-500 Gy were inhibitory. Development of longer pollen tubes was favored by lower doses of γ-rays while higher doses favored development of smaller pollen tubes. 10 ppm of IAA and GA promoted both pollen germination and pollen tube elongation, 25 and 50 ppm of IAA and GA and all the concentrations of kinetin (10-50 ppm) inhibited pollen germination and tube growth. In combination treatments 10 ppm of IAA and GA could ameliorate radiation injury but 25 and 50 ppm of IAA and GA as also 10-50 ppm of kinetin further enhanced radiation damage. Thus in the present study 10 ppm of IAA and GA were radioprotective while 25 and 50 ppm of IAA and GA and 10-50 ppm of kinetin functioned as radiosensitiser.

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