Joao Marcelo Santos de Oliveira

Histology of embryogenic responses in soybean anther culture

In order to clarify the embryogenic responses in soybean anther culture, anthers of four cultivars were cultured under known conditions to trigger androgenic response. A histological study was performed with anthers in vivo and with approximately 100 explants sampled after 9, 12, 15, 18, 21, 30 and 45 days of culture. In vitro culture triggered the frequent accumulation of phenolic compounds on the locular and anther surfaces, and also caused the destruction of cells and tissues in complex structure such as the tapetum, microspores and pollen grains. Somatic embryogenesis of unicellular origin was observed from the epidermis and the middle layer, and of multicellular origin from connective calluses. No androgenic response could be observed in the anthers of these four soybean genotypes, in the medium and conditions indicated. We point out to the need of changing the approach to the study of androgenesis in soybean, either by using culture conditions unfavourable to the proliferation of diploid tissues, or by culturing isolated microspores.

Anther culture and cold treatment of floral buds increased symmetrical and extra nuclei frequencies in soybean pollen grains

Androgenic response is characterized by a multinucleate or multicellular stage of pollen development. Histological sections stained with toluidine blue and squashes in propionic-carmine and in 4′-6-diamidino-2-phenylindole (DAPI) were used for serial observations (0, 14 and 28xa0days) in soybean pollen grains from cultured anthers and floral buds submitted to cold treatment at 4xa0°C. In a total of 62,536 pollen grains, it were observed general averages of 2.06% of pollen grains with two symmetrical nuclei and of 1.41% pollen grains with typical extra nuclei (i.e. additional nuclei with typical morphology). Symmetrical and extra nuclei frequencies increased in both treatments but only the number of pollen grains with typical extra nuclei increased significantly with time of exposure to treatments. In addition, 8.59% of multinucleate pollen grains were recorded with atypical nuclei, smaller than vegetative or generative-types and with a fragmented shape. The frequency of these grains increased significantly with time of exposure to treatments. Thus, soybean multinucleate grains occurrence was not an exclusive response to culture. These preliminary results point to the need of further studies to clarify the relationship between typical and fragmented extra nuclei with both androgenesis and programmed cell death.

Desenvolvimento floral e estaminal no clone CP76 de Anacardium occidentale L.: cajueiro-anão precoce (Anacardiaceae)

The early floral development as well as anther ontogeny in the Anacardium occidentale L. was studied. The flowers present five sepals and five petals with helical and unidirectional development, respectively, and androceum with a stamen with striking heterochronic and heteromorphic development in relation to the remaining nine stamens. At the terminal position an unilocular carpel arises. The histogenic processes is identical in both stamens. At the end of ontogeny both anther types possess four sporangia, with epidermis, endothecium, two middle layers and secretory tapetum, as parietal layers and a sporogenic tissue. The inner portion of the tapetum does not arise from the connective.

Grãos de pólen anômalos no clone CP76 de Anacardium occidentale L. (Anacardiaceae)

Anomalies of male gametophyte development was observed during anther development investigation in the clone CP76 of Anacardium occidentale. Androspores that stop development before the first pollen mitosis, and grains that show male gametophyte anomalies in early stage of development, was observed. The anomalous first mitosis generate two identical cells, or quite, or grains where cell plate was partially formed. Nuclear fusion occurs in those cells where partial cell walls were formed. The interruption of development before first pollen mitosis occurs in high frequency, on the other hand, the anomalies related with the first pollen mitosis are very rare.