Clara H. Ramos

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

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 T alata. They are 31 ± 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, Vaphylla and G divaricatus display a chromocentric nuclear organization. The nuclear similarities between L schismatica and T alata suggest extremely close phylogenetic relationships between them.

Cytochemical and immunocytochemical studyof nuclear structures of Lacandonia schismatica

Summary— The interphase nucleus of the cells of several tissues of Lacandonia schismatica was studied using electron microscopy cytochemical and immunocytochemical methods. The EDTA staining procedure, preferential for RNP, contrasted the Lacandonia granules and perichromatin fibrils. These granules were found to be relatively resistant to RNAse hydrolysis, but they were easily digested if RNAse treatment was carried out after a short hydrolysis with pronase. Bismuth oxynitrate stained granular structures about 17 nm in diameter and the periphery of a few Lacandonia granules. The anti=snURNPs bound to RNP‐containing fibrils in the perichromatin and interchromatin space and also to the periphery of some Lacandonia granules. Immunolabeling of DNA demonstrated numerous filaments of extended chromatin in the perichromatin and interchromatin spaces which were closely related to Lacandonia granules. These observations suggested that Lacandonia granules are equivalent to Balbiani ring granules of nuclei with polytene chromosomes and to perichromatin granules of other plant and animal nuclei. The small number of Lacandonia granules labeled in their periphery by anti‐snURNP mAb were interpreted as being immature granules in the process of formation. The external or annular part of the ring‐shaped structures is heavily labeled by anti‐URNP mAbs but scarcely stained by the EDTA procedure. These features indicate that this region contains abundant proteins associated with snURNAs but probably little snURNAs. The synaptonemal‐like complexes previously found in the interphase nuclei of Lacandonia are formed by two parallel masses of compact chromatin, which react with anti‐DNA, and a central clear space crossed by fiber. Most of these fibers do not react with tests for DNA or RNA and are probably composed of proteins. The EDTA procedure contrasts some fibrils at the internal aspect of the masses of compact chromatin, suggesting the presence of remnants of the lateral element of a synaptonemal complex.