New evidence that Lacandonia granules are ultrastructurally related to perichromatin and Balbiani ring granules.

Lacandonia granules are abundant non-typical extranucleolar ribonucleoprotein particles found in the nucleus of Lacandonia schismatica, a rare plant showing spatial inversion of sex organs. In the present study, changes in the number of Lacandonia granules during flower development, and the presence of SR proteins and poly(A)+ RNA in the nuclei of L. schismatica were analyzed by electron microscopy, immunoelectron microscopy and ultrastructural in situ hybridization. Our results show an important reduction in the number of Lacandonia granules in the nuclei of cells of opened (post-anthesis) in relation to unopened (pre-anthesis) flowers, where granules are very abundant. The SR family of splicing factors and poly(A)+ RNA are present in both perichromatin fibers and Lacandonia granules. The developmental behavior, the presence of SR proteins, recently involved in post-splicing events, poly(A)+ RNA and the reported absence of snRNPs splicing factors in Lacandonia granules, suggest that these particles are involved in postranscriptional events as storage and/or transport of mRNAs. A similar situation is present in other nuclear RNP as perichromatin granules present in mammals and Balbiani ring granules of salivary glands of Chironomus. Based on similarities in morphological, developmental behavior, immunocytochemistry and in situ hybridization results, we conclude that Lacandonia, perichromatin and Balbiani ring granules may be also functionally similar structures.