Dalvir Kaur

Cytomixis and associated meiotic abnormalities affecting pollen fertility in Clematis orientalis

Present cytological investigations from the cold desert regions of Lahaul-Spiti and Kinnaur (India) record the first ever tetraploid (2n=32) chromosome count and cytomixis in Clematis orientalis L. var. acutifolia Hook. f. et Thoms. The phenomenon of cytomixis (9.33–29.80 %) involving chromatin transfer among 2–3 proximate pollen mother cells (PMCs) during male meiosis occurs through narrow and broad cytoplasmic channels from early prophase to tetrad stage. However, frequency of its occurrence during the later meiotic stages is rather low. Chromatin transfer results into the formation of hypo-, hyperploid and enucleated PMCs. Various meiotic abnormalities associated with cytomixis such as chromatin stickiness, pycnotic chromatin, interbivalent connections, out of plate bivalents, late disjunction of bivalents, and laggards and bridges resulted into some pollen sterility (16.33–49.30 %) and heterogeneous pollen grains size.

Impaired Male Meiosis due to Irregular Synapsis Coupled with Cytomixis in a New Diploid Cytotype of Dianthus angulatus (Caryophyllaceae) from Indian Cold Deserts

Dianthus angulatus (Caryophyllaceae) is cytologically examined here for the first time for the area of India. The diploid chromosome count of 2n = 30, ascertained here, represents a new cytotype, supplementing the earlier report of a hexaploid cytotype with 2n = 90 from outside of India. We report here the occurrence of two plants showing impaired meiosis due to irregular synapsis and cytomixis collected from Kinnaur district, Himachal Pradesh (India). The other plants of this species collected in Lahaul-Spiti region showed normal male meiosis (n = 15) with a high (95%−100%) pollen fertility and normal seed set, and they reproduce sexually. Irregular synapsis in two plants from the Kinnaur region is characterized by the complete absence of chromosome pairing and the presence of 30 univalents at diakinesis and meta-anaphase. In addition, other meiotic irregularities were found, such as unoriented chromosomes, laggards, precocious movements of univalents at anaphase-I and micronuclei at telophase. Microsporogenesis was also abnormal, resulting in the formation of monads, dyads, triads, polyads, and tetrads with micronuclei. The occurrence of intra- and intermicrosporal chromatin material transfer during microsporogenesis was observed, which is a rather rarely observed phenomenon. The synaptic irregularities coupled with chromatin transfer in these plants seem to be responsible for the high pollen sterility (38%−42%) and heterogeneously sized pollen grains. In these plants no seeds were set, and plants reproduced vegetatively through root suckers.

Persistent occurrence of meiotic abnormalities in a new hexaploid cytotype of Thalictrum foetidum from Indian cold deserts

Thalictrum foetidum L. (Ranunculaceae), a morphologically variable and widely distributed species of temperate and alpine Himalayas is worked out cytologically for the first time from India. Earlier studies from outside India were restricted to chromosome counts and karyotypic analysis. We studied the male meiosis, microsporogenesis and pollen viability in the wild accessions from the cold deserts of Lahaul-Spiti, Kinnaur and Pangi Valley of Himachal Pradesh. Present cytomorphological surveys in the species record the existence of two distinct morphotypes involving plant size; colour and size of leaf/leaflet; dentation of leaflet lobes; and degree of leaf pubescence. All the accessions in the two morphovariants share the same meiotic chromosome number (n = 21) and adds a new intraspecific hexaploid cytotype. The accessions show the phenomenon of cytomixis involving transfer of chromatin material among proximate pollen mother cells (PMCs) and associated meiotic abnormalities like, out of plate bivalents, interchromosomal connections, and laggards, bridges and micronuclei at anaphases/telophases. Microsporogenesis results into abnormal sporads (tetrads with micronuclei, dyads, triads and polyads). The products of such sporads resulted into some pollen sterility and pollen grains of heterogeneous sizes. The persistent occurrence of phenomenon of cytomixis and associated meiotic abnormalities and consequently pollen sterility and pollen grains of heterogeneous sizes in the hexaploid cytotype of T. foetidum seems to be under some genetic factors associated with the genome.

Structural heterozygosity and cytomixis driven pollen sterility in Anemone rivularis Buch.-Ham. ex DC. from Western Himalaya (India)

Meiotic studies have been carried out on 12 accessions of Anemone rivularis from different regions of Western Himalaya. The accessions from Chamba, Kullu and Kinnaur districts of Himachal Pradesh and Uttarkashi district of Uttarakhand showed a normal meiotic course leading to high pollen fertility (87–100%). However, the accession scored from Saat Tal, Uttarakhand showed structural heterozygosity for reciprocal translocations. This is the first report of occurrence of structural heterozygosity in the species. Out of the 604 analysed pollen mother cells (PMCs), 38.41% (232) showed quadrivalent formation at diakinesis and metaphase-I. Comparison of chiasma frequency was also performed among selected populations using one-way analysis of variance (ANOVA), which showed significant differences. The occurrence of cytomixis involving inter PMC transfer of chromatin material among neighbouring meiocytes (45.68%) was also observed. PMCs at anaphases/telophases showed laggards (31.25%) and chromatin bridges at A-I/T-I and A-II/T-II (21.02%) leading to abnormal microsporogenesis. Consequently, abnormal sporads such as triads (66.67%), polyads (3.33%) and triads with micronuclei (0.83%) were formed. Structural heterozygosity and inter PMC chromatin material transfer in the individuals of the species seem to be responsible for the reduction in pollen fertility (67.8%) and formation of pollen grains of heterogeneous sizes.

A profile of male meiosis, chromosomal variation and status in species of Impatiens from North-West Himalaya in India

Abstract Impatiens (Balsaminaceae), a genus of over 1000 species, is represented by 209 species in India, particularly in South India and Himalayas. In spite of attempts made by several Indian cytologists, the chromosome counts are available for only 95 species, through karyological studies, or pollen mitosis or meiotic preparations. The investigated species revealed a considerable amount of dysploid chromosomal variation. We have studied male meiosis in 53 accessions from 14 species collected from unexplored regions of North-West Himalaya in India. Chromosome numbers were confirmed for nine species and numbers different from earlier records were found in five species. Four species were documented for chromosome counts for the first time. Out of the 14 species covered presently, nine species possessed dysploid cytotypes with different diploid chromosome counts. Five species possessed more than one diploid chromosome counts. Dysploidy seems to be quite favourable for causing chromosomal variation in the genus. Based on compiled chromosomal data, it is apparent that there is a lot of variation in base numbers. Among the different basic numbers prevalent in the genus, we are of the opinion that x = 7, x = 8, x = 9 and x = 10 seem to be the most common. In addition, a list of North-West Himalayan species of the genus which are yet to be worked out chromosomally and those depicting chromosomal variation has also been included.