Ploidy reduction and genome segregation in cultured carrot cell lines. II. Somatic meiosis

Abstract

Carrot cell lines Wl and W2 express permanently in culture a meiotic-like phenotype, with apparent pairing and chiasmata formation comparable to meiosis during carrot microsporogenesis. The variant lines also show several variants of division in relation to the presence or absence of cytokinesis, nuclear fusion or spindle disturbance.The meiotic-like divisions can also be found in the abnormal structures, which are regenerated from these spontaneous variant lines. A possible role of the chromosome reducing mechanisms on carrot embryogenesis capacity and somaclonal variability is postulated.

Morphogenic Aspects of Somatic Embryogenesis

“…The down-regulation of gene expression that occurs upon exposure to an auxin or to a stress factor might resemble that which occurs during sporogenesis [22]. Meiotic divisions have been observed in cell cultures of carrot [23], and structural elements in common with megagametophytes have been observed in soybean embryogenic tissue [24]. After induction, embryo-specific DNA methylation patterns may also help regulate embryogenesis [25].…”

“…Altered ploidy levels are also associated with loss of embryogenicity. Non-embryogenic carrot lines exhibited ploidy reduction via somatic meiosis [23] and reduced embryogenicity in yellow-poplar suspension cultures was associated with a high frequency of haploid cells [281]. Apart from ploidy reduction, Kott et al [282] noticed an increase in ploidy levels in embryogenic callus that originated from haploid barley embryos.…”

Ploidy reduction and genome segregation in cultured carrot cell lines. I. Prophase chromosome reduction

“…Prophase chromosome reduction, reductional grouping and somatic meiosis, described in this and in the accompanying paper, also frequently occur in fast growing cells of other species cultured in vitro (Nuti Ronchi 1990). Similar phenomena have been reported in the past to occur in plants after chemical treatments (Huskins 1948;Mehra 1986) or under natural conditions, but often have been dismissed as due to bad fixations.…”

“…In this, and in the accompanying paper (Nuti Ronchi et al 1992) we describe the results of a cytological analysis of some carrot cell lines, several years old or recently constituted, obtained from different laboratories. Although the small size of the carrot chromosomes does not offer easy material, we have been able to detect some cytological chromosome-reducing mechanisms, not described before in cell tissue culture.…”

Historical Insights into Some Contemporary Problems in Somatic Embryogenesis

“…e.g. Nuti Ronchi et al, 1992 andCannan, 1997 for some novel perspectives). Obviously a cell that has been killed and sectioned and shows no internal divisions provides no irrefutable C\idencc that it represents the 'nonn' in an embryogenic culture (e.g.…”