Sporogenesis and development of gametophytes in an endangered plant, Tetracentron sinense Oliv

The sporogenesis and development of gametophytes in Tetracentron sinense Oliv. were studied with light microscopy. The anther has four microsporangia; its primary anther wall consists of an epidermis, an endothecium, one or two middle layers and one glandular tapetum. Simultaneous cytokinesis follows meiosis, forming a tetrahedral tetrad. Mature pollen grains are two-celled at the time of anther dehiscence. Its ovule is anatropous, bitegmic and crassinucellate; the development of the female gametophyte is of the monosporic 8-nucleate Polygonum type. Significantly, some striking features were first found in T. sinense: (1) anther dehiscence occurs soon after the endothecium fibrously thickens and the intersporangial septum degenerates; (2) tapetum degeneration is retarded, persisting up to the stage of two-celled pollen grain; (3) a few cellular events such as the vacuolization and the contraction and deformation of the pollen mother cell (PMC) and microspore are not normal at the PMC, dyad and tetrad stages. The abnormalities during male reproduction might be one of important factors resulting in the poor natural regeneration of T. sinense.

Anther and pollen development in some species of Poaceae (Poales) / Desenvolvimento da antera e do grão de pólen em espécies de Poaceae (Poales)

Anther and pollen development were studied in Olyra humilis Nees, Sucrea monophylla Soderstr, (Bambusoideae), Axonopus aureus P. Beauv., Paspalum polyphyllum Nees ex Trin. (Panicoideae), Eragrostis solida Nees, and Chloris elata Desv. (Chloridoideae). The objective of this study was to characterise, embryologically, these species of subfamilies which are considered basal, intermediate and derivate, respectively. The species are similar to each other and to other Poaceae. They present the following characters: tetrasporangiate anthers; monocotyledonous-type anther wall development, endothecium showing annular thickenings, secretory tapetum; successive microsporogenesis; isobilateral tetrads; spheroidal, tricellular, monoporate pollen grains with annulus and operculum. Nevertheless, the exine patterns of the species studied are distinct. Olyra humilis and Sucrea monophylla (Bambusoideae) show a granulose pattern, whereas in the other species, it is insular. In addition, Axonopus aureus and Paspalum polyphyllum (Panicoideae) have a compactly insular spinule pattern, while Chloris elata and Eragrostis solida (Chloridoideae) show a sparsely insular spinule pattern. The exine ornamentation may be considered an important feature at the infrafamiliar level.

O desenvolvimento da antera e do grão de pólen de Olyra humilis Nees, Sucrea monophylla Soderstr. (Bambusoideae), Axonopus aureus P. Beauv., Paspalum polyphyllum Nees ex Trin. (Panicoideae), Eragrostis solida Nees and Chloris elata Desv. (Chloridoideae) foi estudado visando caracterizar embriologicamente essas espécies de subfamílias consideradas basal, intermediária e derivada, respectivamente. As espécies são similares entre si e entre as demais Poaceae. Apresentam os seguintes caracteres: anteras tetrasporangiadas; desenvolvimento da parede da antera do tipo monocotiledôneo, endotécio com espessamento de parede anelar, tapete secretor; microsporogênese sucessiva; tétrades isobilaterais; grãos de pólen esféricos, tricelulares, monoporados, com anel e opérculo. Por outro lado, o padrão de ornamentação da exina do grão de pólen é distinto. Olyra humilis e Sucrea monophylla (Bambusoideae) apresentam padrão granuloso e as demais espécies padrão insular. Axonopus aureus e Paspalum polyphyllum (Panicoideae) apresentam espínulos densamente agrupados, enquanto Chloris elata e Eragrostis solida (Chloridoideae) espínulos esparsamente agrupados. A ornamentação da exina dos grãos de pólen pode ser considerada caráter importante a nível infrafamiliar.

Contenido microbiológico cultivable del tracto intestinal y polen almacenado de Apis mellifera (Hymenoptera: Apidae) / Cultured Microbiological Content of the Intestinal Tract and Stored Pollen of Apis mellifera (Hymenoptera: Apidae)

Se caracterizaron los microorganismos cultivables asociados con Apis mellifera. Las muestras fueron tomadas a partir de polen almacenado (joven y maduro) y transportado en corbículas y tracto digestivo de las abejas (forrajeras y recién nacidas). Se aislaron bacterias pertenecientes a los géneros Pseudomonas, Streptococcus, Micrococcus, Lactobacillus, Klebsiella, Proteus, Yersinia y Arthrobacter y hongos de los géneros Rhizopus, Alternaria y Epicoccum. De acuerdo a sus propiedades bioquímicas, algunas de estas bacterias pueden estar involucradas en la degradación de los compuestos de la capa externa del polen y son adquiridas por las abejas a través del alimento y contacto con otros individuos de la colmena. La presencia de los hongos se explica por su amplia distribución en el ambiente, ya que los tres géneros se encuentran comúnmente en el suelo y en las plantas que las abejas pueden seleccionar como fuente de alimento.

Symmetric pollen mitosis I and suppression of pollen mitosis II prevent pollen development in Brachiaria jubata (Gramineae)

Microsporogenesis and pollen development were analyzed in a tetraploid (2n = 4x = 36) accession of the forage grass Brachiaria jubata (BRA 007820) from the Embrapa Beef Cattle Brachiaria collection that showed partial male sterility. Microsporocytes and pollen grains were prepared by squashing and staining with 0.5 percent propionic carmine. The meiotic process was typical of polyploids, with precocious chromosome migration to the poles and laggards in both meiosis I and II, resulting in tetrads with micronuclei in some microspores. After callose dissolution, microspores were released into the anther locule and appeared to be normal. Although each microspore initiated its differentiation into a pollen grain, in 11.1 percent of them nucleus polarization was not observed, i.e., pollen mitosis I was symmetric and the typical hemispherical cell plate was not detected. After a central cytokinesis, two equal-sized cells showing equal chromatin condensation and the same nuclear shape and size were formed. Generative cells and vegetative cells could not be distinguished. These cells did not undergo the second pollen mitosis and after completion of pollen wall synthesis each gave rise to a sterile and uninucleate pollen grain. The frequency of abnormal pollen mitosis varied among flowers and also among inflorescences. All plants were equally affected. The absence of fertile sperm cells in a considerable amount of pollen grains in this accession of B. jubata may compromise its use in breeding and could explain, at least in part, why seed production is low when compared with the amount of flowers per raceme.