Karyological and cytogenetic features of conifers in arboretums and parklands

Aim. The study of karyological and cytogenetic features of conifers growing under conditions of introduction and increased recreational pressure, to identify biodiversity and solve the problems of population and environmental genetics of representatives of this group of plants. Methods. Classical chromosome research methods with staining with acetohematoxylin were used. Results. In species, forms, and cultivars of conifers from the Pinaceae and Cupressaceae families growing in arboretums and parklands, as well as being components of green spaces in settlements of different geographical regions, variability of chromosome numbers (mixoploidy), the appearance of B chromosomes, high occurrence, and a wide range of chromosomal and meiotic anomalies are discovered. Conclusions. Karyological and cytogenetic studies have shown the presence of karyotypic polymorphism and an increase in the number of various disorders of mitosis and meiosis in conifers when introduced under growing conditions in recreational areas. Keywords: conifers, introduction, chromosome number, chromosomal rearrangements, meiosis disorders.

Diploid male gametes circumvent hybrid sterility between Asian and African rice species

In F1 hybrids of Oryza sativa (Asian rice) and O. glaberrima (African rice), heterozygosity leads to a complete gamete abortion because of allelic conflict at each of the 13 hybrid sterility (HS) loci. We systematically produced 19 plants from the F1 hybrids of both the rice species by the anther culture (AC) method. Five of the 19 interspecific hybrid plants were fertile and able to produce seeds. Unlike ordinal doubled haploid plants resulting from AC, these regenerated plants showed various ploidy levels (diploid to pentaploid) and different zygosities (completely homozygous, completely heterozygous, and a combination). These properties were attributable to meiotic anomalies in the interspecific hybrid F1 plants. Examination of the genetic structures of the regenerated plants suggested meiotic non-reduction took place in the interspecific hybrid F1 plants. The centromeric regions in the regenerated plants revealed that the abnormal first and/or second divisions of meiosis, namely the first division restitution (FDR) and/or second division restitution (SDR), had occurred in the interspecific hybrid. Immunohistochemical observations also verified these phenomena. FDR and SDR occurrences at meiosis might strongly lead to the formation of diploid microspores. The results demonstrated that meiotic anomalies functioned as a reproductive barrier occurred before the HS genes acted in gamete of the interspecific hybrid. Although such meiotic anomalies are detrimental to pollen development, the early rescue of microspores carrying the diploid gamete resulted in the fertile regenerated plants. The five fertile plants carrying tetraploid genomes with heterozygous alleles of the HS loci produced fertile diploid pollens, implying that the diploid gametes circumvented the allelic conflicts at the HS loci. We also proposed how diploid male gametes avoid HS with the killer-protector model.

Chromosome count, meiotic abnormalities and pollen sterility in Lahaul sweetvetch (Hedysarum astragaloides Benth. ex Baker, Fabaceae), an endemic and threatened species from India

Male meiotic studies were carried out on eight different accessions of Hedysarum astragaloides Benth. ex Baker (Fabaceae), an endemic and threatened species of northwest Himalaya, India. Although genetic factors such as meiosis, chromosome number, and ploidy level may be causative for the evolution, endemism, rare distribution or even extinction of the species, no detailed information exists. Keeping this in mind H. astragaloides has been studied cytologically. Male meiotic investigations revealed diploid level (2n=2x=14) for species and normal meiotic course in the accessions from the Manali Hills resulting in nearly 100% pollen fertility. However, the accessions scored from the Manimahesh Hills and Pangi Valley depicted inter-pollen mother cell transfer of chromatin material and structural heterozygosity for reciprocal translocations. Consequent upon these meiotic anomalies, some pollen sterility (21%) resulted. On account of this sweeping genetic outcome, the incidence of anomalies such as this in an endemic and threatened species warrants grave consideration. It is sensible to conclude that conservation measures should include the collection of germplasm from the localities where plants are meiotically stable with high gametic fertility, to ensure good germination and healthy plants for future use. Seeds from meiotically normal individuals should be given priority for inclusion in seed banks.

Meiotic behaviour and morpho-phenological variation in cut stock (Matthiola incana L.) flower

Morpho-phenological and meiotic studies were performed in twelve cultivars of Matthiola incana. All of the cultivars were diploid (2n = 2x = 14) with basic chromosome number x = 7. A number of aneuploid PMCs (n + 1) were observed in plants of two cultivars, named ‘Nobel’ (NB) and ‘Goddess’ (GD), at the diakinesis stage. Trisomic individuals with the frequency of 20% and 5% and (2n + 1 = 15) somatic chromosomes were observed in seeds obtained from single-flowered plants of the cultivars NB and GD, respectively. An additional chromosome was mostly observed in the form of a chain trivalent or a rod univalent. Various meiotic abnormalities were found in all the cultivars to different degrees. In these cultivars, the percentage of cells with meiotic abnormalities was higher in anaphase I. Cytomixis was observed for the first time in Matthiola incana. ANOVA tests revealed significant differences in morpho-phenological characteristics. ‘Nobel’ differs from the others in all of the vegetative features investigated in this study. All the cultivars studied except ‘Nobel’ and ‘Pacific Crimson’ possessed high pollen fertility (> 90%). Five groups of the cultivars based on morpho-phenological features disagree with the clustering of cultivars based on meiotic traits. It is thought that the various morpho-phenological features observed among the cultivars could be due to their different genetic background and not only to meiotic anomalies.

EMS, sodium azide and gamma rays induced meiotic anomalies in Delphinium malabaricum (Huth) Munz

Meiotic cell division is a dynamic cellular process controlled by a large number of genes that act from premeiotic to postmeiotic mitosis. Mutation in these genes may cause anomalies that impair plant fertility. In this study, an attempt has therefore been made to understand the effects of ethyl methane sulfonate (EMS), sodium azide (SA) and gamma rays on the meiotic configuration of Delphinium malabaricum. The results demonstrated that the mutagens cause various types of cytological aberrations, such as univalents, chromatin bridges, laggards, fragments, stickiness and multinucleated cells. The maximum aberrations were found at higher doses/concentrations of the mutagens. The highest percentage of pollen mother cells showing abnormalities was induced by EMS followed by gamma rays and SA. The mutagen impact on chromosomal anomalies increased the frequency of pollen sterility.