Variable multivalent orientations during diakinesis and metaphase I in microsporocytes ofTradescantia spathaceaSw.

Abstract

Meiotic studies carried out on seven plants/clones of Tradescantia spathacea did not show the expected ring of 12 chromosomes in any of the 1765 cells studied at diakinesis (1202 cells) and metaphase I (563 cells). While at diakinesis the chromosomes resolved into chain configurations of all lengths ranging from one through 12 chromosomes, with the mean per cell being 2.47 ± 1.28, at metaphase I chains carrying up to 10 chromosomes were seen and the mean per cell was 4.18 ± 1.47. However, the larger chains were not the most frequent configurations observed at the two stages. Bivalents and univalents were the most frequent configurations observed in 38.68 and 43.92% cells at diakinesis and 63.94 and 57.72% cells at metaphase I, followed by chains of 10 (29.95% cells) and chains of three (51.50% cells) at the two stages, respectively. The larger chains, though visible at both the meiotic stages, varied significantly in the centromere orientation patterns. While at diakinesis they predominantly showed linear or indifferent orientation, at metaphase I 83.25% chains showed alternate orientation, with the rest showing linear and/or indifferent orientation. A high frequency of alternate orientation was observed in chains of three chromosomes (93.93%), followed by the chains of five and four, where 74.19 and 71.27% chains appeared in alternate orientation, respectively. In 4.97% cells with two chains of six chromosomes each, contrasting behavior was noticed in the two chains in respect of orientation. While one chain appeared zigzagged with alternate centromeres facing the same pole, the other chain invariably appeared in linear configuration. As a result of complex configurations at metaphase I and the high frequency of univalents, anaphase I segregation of chromosomes was highly irregular with 84% cells showing 1-3 lagging chromosomes. The average pollen viability determined for the seven clones studied was very low (17.87 ± 2.57%). The probable cause(s) of the different behaviors of the chain multiples at the two meiotic stages is discussed.

Inter-telomeric connections and achiasmate meiosis in Tradescantia spathacea Sw.

“…While inter chromosomal connections have been attributed mostly to fixation artifact [33] and to the fusion of heterochromatic region between the chromosomes [16,39,62,65], achiasmate meiosis has been assigned to the presence of mutant gene(s) affecting chiasmata formation [2,21,32,34,60], alteration in temperature/humidity [34,60,67], defective synaptonemal complex formation [14,21,24,60] and to disturbed supply of potassium and phosphate ions to the tissue [2,60]. In the present material inter-telomeric connections cannot be attributed to any of the two factors mentioned elsewhere on account of the fact that this feature was discerned only in some buds while other buds showed meiotic features characteristic of complex translocation heterozygote and supported the earlier reports [17,18,31,36,37,41,42,55,56,64]. Similarly, based on the earlier observations of the presence of heterochromatin exclusively in the centromeric region and their absence from the telomeric ends in majority of the chromosomes in T. spathacea [19,47], one can rule out the possible involvement of heterochromatin in generating intertelomeric connections.…”

“…On average anthers taken from about 20-25 flower buds were squashed for meiotic studies. Although chromosome behavior was studied in eleven plants, this communication reports the details of only one plant as the meiotic observations made in ten other plants were much in accordance with the observations made by earlier workers [36,37,41,42]. Nevertheless, the salient features of meiosis, recorded at various stages of meiosis I, in ten plants are given in Tables 1, 2 and 3.…”

“…While in maize mutation in meiosis-specific proteins resulted in pairing between non homologous chromosomes [49], in male Drosophila mutation in meiotic proteins led to the formation of thin thread like connections between non homologous chromosomes [23,29]. Considering the aforementioned research findings and also the fact that in T. spathacea the chromosome pairing and the chiasmata formation, presently preempted by inter telomeric connections, are confined exclusively to chromosome ends [37,50,61], it is proposed that some alteration may have occurred in the DNA protein complex that constituted the telomere, presumably by some alteration in the cellular chemical environment which not only suppressed the functional homology between the chromosome ends resulting in achiasmate meiosis but also induced ectopic fusion between the chromosomes by forming inter telomeric connection. Whether these connections were formed between the homologous or non homologous region was not clear.…”

Spontaneous Occurrence of Structural Heterozygosity in ‘Buckwheat’ (<i>Fagopyrum acutatum</i>) from the Parvati Valley, Himachal Pradesh, India

“…Consequently, 50% non-viable gametes are produced toward pollen side and 50% toward ovule side. Such a phenomenon of structural heteozygosity leading to some sterility of pollen grains has been reported in a number of cases namely, Chrysanthemum coronarium (Gill and Gupta 1981), C. zawadskii (Kim et al 2008), Lathyrus boissieri (Ghaffari et al 2009), Artemisia parviflora , Euphorbia pilosa (Saggoo and Farooq 2011), Astragalus chlorostachys (Rana et al 2012), Tradescantia spathacea (Koul et al 2013), Saxifraga diversifolia (Kumar and Singhal 2013), Achillea millefolium (Singhal et al 2014) and Anemone rivularis (Kumar et al 2015). Complete male sterility due to reciprocal translocations has also been reported in Allium consaguineum (Gohil and Koul 1978) and Allium roylei (Sharma and Gohil 2003, Kohli and Gohil 2011, Kohli and Koul 2013.…”

Structural Heterozygosity for Reciprocal Translocation in <i>Tanacetum artemisioides</i> Sch. Bip. ex Hook. f. from Ladakh Division of Jammu and Kashmir

“…In the presently studied accession of Tanacetum artemisioides, the majority of the PMCs showed the adjacent type of orientation of quadrivalents/hexavalents (ring or chain) and the alternate (zigzag) orientation was seen in only one PMC, resulting in a considerable amount of pollen sterility (30-35%), which appears to be the result of duplications and deficiencies of genes as mentioned by Ghosh and Datta (2006) in Nigella damascene. Similar effects of structural heterozygosity leading to nonviable pollen grains have been reported in a number of plants, namely, Citrus jambhiri (Singhal and Gill 1981), Chrysanthemum zawadskii (Kim et al 2008), Artemisia parviflora (Gupta et al 2010), Astragalus chlorostachys (Rana et al 2012), Saxifraga diversifolia (Kumar and Singhal 2013), Tradescantia spathacea (Koul et al 2013), Achillea millefolium (Singhal et al 2014), and Anemone rivularis (Kumar et al 2015). Gohil and Koul (1978) and Sharma and Gohil (2003) have reported that structural heterozygotes of Allium consanguineum and A. roylei depict complete gametic sterility due to reciprocal translocations.…”