Cellular approach to the study of androgenesis in maize anthers: Immunocytochemical evidence of the involvement of the ubiquitin degradative pathway in androgenesis induction

Maize anthers in the late-uninucleate stage, corresponding to a DH 109 x ZK 191/a F1 hybrid line, were induced to produce embryoids by cold pre-treatm ent and incubation onto a modified YP medium. LM observation of sections of the anthers showed the existence of bicellular microspores two days after starting the culture. Several types of multicellular microspores (MCM) and multinucleate microspores (MNM) appeared from the fifth day after culture o nwards, together with many degenerated, non-induced microspores. This abund ance of forms reveals the presence of different patterns of division and de velopment. Ultrastructural observation of these cellular forms showed parti cular features, such as the presence of numerous nuclear pores in early sta ges of induction and the formation of a thick independent cell wall underne ath the microspore intine. A certain degree of polarity in these structures was also frequently observed. Proembryoids appeared after 10-13 days of cu lture, whereas embryo-like structures were observed several days later (16 days of culture). Immunocytochemical studies were carried out on semithin sections of the ant hers using a commercially available polyclonal antibody to ubiquitin. Sligh t labeling nas consistently found in most cell types, excluding degenerated and non-induced microspores. The intensity of the labeling was found to be substantially greater in putative androgenic MCM. A model for the involvem ent: of the ubiquitin-mediated degradation pathway in pollen cell cycle con trol and androgenesis induction is proposed.