Abstract
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 .
 
 
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