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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.

A gall is the result of complex interactions between a gall inducing-insect and its host plant. Certain groups of insects have the ability to induce a new structure, a gall, on plant organs by altering the normal growth of the host involved plant organ. The gall usually provides shelter and nutrients, in addition to protection against adverse environmental conditions and natural enemies to the inducing insect and its offspring. The ecological uniqueness of a gall is that it allows the inducing-insect to complete their life cycles. In this study, we have described the structures of different stages of growth of a gall induced by Amphibolips michoacaensis on the buds of leaves on Quercus castanea (Fagaceae) to know the subcellular changes during development. The gall consist of various layers such as a nutritive tissue, a lignified sheath, a spongy layer and an outermost epidermis around a centrally located larval chamber. The nutritive cell of the larval chamber show nuclear and nucleolar hypertrophy in the early phases of growth. The granular profile of the nucleolus suggests an active synthesis of ribosomes indicating an accelerated protein synthesis in these cells. During early stages of growth, the cells of the spongy layers within galls are nucleate and nucleolate and include amyloplasts, and the cytoplasm is less abundant. During later growth stages, the spongy cells are enucleate and enucleolate. Chloroplasts occur in the epidermal cells during early stages of growth, indicating that galls are photosynthetically active in early stages of growth. During intermediate stages of growth, a gradual loss of cellular components occurs commencing in the epidermal cells and progressing towards the nutritive cells.

En este trabajo se caracterizan y comparan las punteaduras, la pared secundaria y la membrana de la punteadura en elementos traqueales en dos especies de Cactaceae con madera contrastante. Se recolectaron individuos adultos de Echinocactus grusonii (madera dimorfa) y Mammillaria compressa (madera no fibrosa) pertenecientes a la tribu Cacteae y se procesaron utilizando diferentes métodos para su observación por microscopía fotónica, electrónica de barrido y de transmisión. Los elementos de vaso tienen placas de perforación simples con un reborde, así como diferentes grados de acumulación de la pared secundaria desde anulares y helicoidales hasta punteaduras pseudoescalariformes y alternas. En M. compressa la pared secundaria en algunos elementos de vaso puede acumularse tanto en forma anular como helicoidal. En E. grusonii , la membrana de las punteaduras alternas en los elementos de vaso tiene poros muy pequeños, apreciables con aumentos altos exclusivamente con microscopia electrónica. En las fibras se observaron organelos núcleo y mitocondrias y un material electrodenso; además el par de punteaduras fibra-fibra tiene un pequeño reborde visto con microscopia electrónica de transmisión no descrito para la familia. Las diferencias en la membrana de la punteadura entre ambas especies posiblemente están relacionadas con su capacidad de evitar embolismos lo que se podrá demostrar con trabajo empírico.