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Background: Nuclear ribonucleoprotein particles play a key role in RNA processing and in the gene expression pathway. Interchromatin granules (GICs) involved in the metabolism of pre-messenger RNA (pre-mRNA) were described in Allium cepa and Chiranthodendron pentadactylon. Other particles as Lacandonia granules (LGs) were found in Lacandonia schismatica as well as Ginkgo biloba and Welwitschia mirabilis. LGs are structures equivalent to perichromatin granules (PCGs) described in mammals and to Balbiani ring granules (BRGs) described in the midge Chironomus tentans. PCGs and BRGs are involved in the metabolism of messenger RNA (mRNA). Here, we analyze the extranucleolar particles from Cycas revoluta and Ceratozamia mexicana and compare them to GICs and LGs using conventional electron microscopy and atomic force microscopy. Species study: Cycas revoluta (Cycadaceae) and Ceratozamia mexicana (Zamiaceae) Hypothesis: The extranucleolar ribonucleoprotein particles in the nuclei of C. revoluta and C. mexicana are equivalent to GICs or GLs. Methods: Fragments of young leaves of C. revoluta and C. mexicana were processed for standard transmission electron microscopy. Thin sections were stained with the EDTA technique preferential for ribonucleoproteins and osmium amine specific for DNA. From the semithin sections the samples were studied with the AFM and images of them were obtained. Results: Ribonucleoprotein particles 32 nm in diameter are present in the interchromatin and perichromatin space in C. revoluta and C. mexicana. Conclusion: Ribonucleoprotein particles present in the cell nuclei of C. mexicana and C. revoluta are ultrastructurally equivalent to LGs. Translate stop Translate stop Translate stop

Background: Lacandonia granules are extranucleolar ribonucleoprotein (RNPs) particles, 32 nanometers in diameter that were first described in the nucleus of Lacandonia schismatica. Cytochemical and immunocytochemical studies suggest that these particles are equivalent to perichromatin and Balbiani ring granules described in mammals and salivary glands cells of the insect Chironomus tentans, respectively. Lacandonia granules are also present in the related Triuris brevystilis, and they were later described in the gymnosperm Ginkgo biloba. These findings suggest that Lacandonia granules have a wider distribution in the plant kingdom. Species study: The plant Welwitschia mirabilis, a gymnosperm of the order Gnetales. Hyphotesis: Lacandonia granules are present in the cell nucleus of W. mirabilis. Methods: Plants were cultivated in a germination chamber and samples of leaves were processed for transmission electron microscopy. Thin sections were stained with the EDTA technique preferential for ribonucleoproteins and osmium amine specific for DNA and observed with a microscopy. Results: Light, electronic and atomic force microscopy revealed that cell nuclei of W. mirabilis display a reticulated arrangement of chromatin. Moreover, granules of 32.17 ± 1.7 nm in diameter were observed among strands of reticulated chromatin. Conclusions: Our results indicate that Lacandonia granules are present in the nuclei of the gnetal W. mirabilis.

Background: The family Fagaceae is one of the most important in temperate regions of the Northern hemisphere. Fagus and Quercus are distributed in Mexico, the former in Northeastern Mexico, while the latter reaches a high diversity in the Sierra Madre Oriental, Mexico. In Hidalgo state, located mainly in the Sierra Madre Oriental, knowledge of the Fagaceae diversity is still uncertain. Questions and/or hypothesis: We carried out a taxonomic revision of the genus and species of Fagaceae in Hidalgo state. We determined how many and which species are distributed in Hidalgo. We also present a morphological description and ecological characters of each one. Studied species: The species of the family Fagaceae Study site: Hidalgo state, Mexico. Method: We collected herbarium specimens, made field observations and reviewed herbarium data of Fagaceae specimens at FCME, INEGI, MEXU, ENCB, SLPM, HUMO, XAL and partly BH herbaria. In addition, we checked taxonomic literature and protologues of each species. Results: We found one species of Fagus and 43 of Quercus, 22 of which belong to the section Quercus (white oaks) and 21 to section Lobatae (red oaks). Morphological descriptions, altitudinal and geographical distribution, vegetation types of each species and a dichotomous key for species identification are presented. Illustrations and photographs of the species are also included. Conclusions: A high diversity of Fagaceae species is present in Hidalgo state. In Mexico, Hidalgo ranks in fifth place for oak species diversity, just behind Oaxaca (50 species), Puebla (50), San Luis Potosí (45), and Jalisco (45).

Se propone e ilustra a Magnolia guerrerensis (Magnoliaceae) como una entidad nueva del bosque mesófilo de montaña en el estado de Guerrero, México. Este taxón es afín a M. schiedeana Schltdl., pero difiere de ésta por presentar estípulas más pequeñas, flores pediceladas y gineceo con menos carpelos. También se incluye una clave para distinguir ambas especies.