The ultrastructural study of the interphase cell nucleus of Lacandonia schismatica (Lacandoniaceae: Triuridales) reveals a non‐typical extranucleolar particle

Abstract

By light and electron microscope cytochemistry we characterized the interphase nucleus of Lacandonia schismatica, the only known species of the new plant family Lacandoniaceae, whose most peculiar feature is the inverted position of the sexual organs, an aspect never found before among flowering plants. Furthermore, we compare it to Triuris alata, a related species, to Voyria aphylla (a dicotyledon), to Gymnosiphon divaricatus (a monocotyledon) and also to saprophytes. The reticulated chromatin of L schismatica and T alata is similar to that of other monocotyledons. In addition, we describe a unique type of RNP granules in the interchromatin space which are about 32 + 3 nm SD in diameter and occur as huge clusters. They are intermediate in size and spatial distribution between inter-and peri-chromatin granules. We term them 'Lacandonia granules'. The granules were also found in Talata. They are 3 ! +_ 2 nm in diameter. No significant differences in size were observed between them (P > 0.05). Synaptonemallike complexes and ring-shaped structures were seen in interphase nuclei of somatic cells of these species. Coiled and nucleolus-associated bodies, as well as centromeres were also found in these two organisms. On the contrary, V aphylla and G divaricatus display a chromocentric nuclear organization. The nuclear similarities between L schismatica and Talata suggest extremely close phylogenetic relationships between them. chromatin / Lacandonia I plant nucleus / ribonucleoproteins

Further Ultrastructural Characterization of the Intranuclear Ring-Shaped Bodies of the Plant Lacandonia schismatica

“…The central core of these bodies may contain ribonucleoproteins (RNPs) (Jiménez-García et al, 1992), as suggested by the preferential EDTA regressive staining of Bernhard (1969), while the external ring is enriched in snRNPs, as observed by immunoelectron microscopy studies (Agredano-Moreno et al, 1994). These data suggest a role for these structures in premRNA metabolism as assembly and/or storage sites of molecular elements involved in the splicing process (Agredano-Moreno et al, 1994).…”

“…The central core of these structures contains ribonucleoproteins (Jiménez-García et al, 1992;Agredano-Moreno et al, 1994), although the EDTA regressive staining (Bernhard, 1969) is not specific but preferential for RNPs. Little to no SR protein is present, however.…”

“…In plants, however, the reticulated and the chromocentric nuclear structures are described based upon heterochromatin arrangement. The nucleus of Lacandonia schismatica E. Martínez and C. H. Ramos (Lacandoniaceae:Triuridales), a rare plant with an inverted position of the sexual organs Má rquez-Guzmá n et al, 1989), is reticulated with a novel type of nuclear particle associated with it (Jiménez-García et al, 1992;Agredano-Moreno et al, 1994; AgredanoMoreno and Jiménez-García, 2000). In addition, the nucleus of this species also displays ring-shaped nuclear bodies.…”

“…The nucleus of Lacandonia schismatica E. Martínez and C. H. Ramos (Lacandoniaceae:Triuridales), a rare plant with an inverted position of the sexual organs Má rquez-Guzmá n et al, 1989), is reticulated with a novel type of nuclear particle associated with it (Jiménez-García et al, 1992;Agredano-Moreno et al, 1994; AgredanoMoreno and Jiménez-García, 2000). In addition, the nucleus of this species also displays ring-shaped nuclear bodies.The ring-shaped bodies of L. schismatica are 0.5-1 m in diameter and they seem to be associated with the nucleolus, found free in the nucleoplasm, or found in close contact with some strands of compact chromatin (Jiménez-García et al, 1992). The central core of these bodies may contain ribonucleoproteins (RNPs) (Jiménez-García et al, 1992), as suggested by the preferential EDTA regressive staining of Bernhard (1969), while the external ring is enriched in snRNPs, as observed by immunoelectron microscopy studies (Agredano-Moreno et al, 1994).…”

Visualization of Cell Structure by Atomic Force Microscopy

“…Using tapping mode on Hep2 cells, images of cell nuclei were obtained and nuclear structures as interchromatin granule clusters were resolved [17]. Previously, nuclear particles named Lacandonia granules [19] were observed individually [13], opening the possibility to analyze gene expression at the nanoscale in situ [20,21]. It is interesting to mention that aspects of cell biology as mitosis have been also studied [12].…”