[Histological and cytological study on the ontogeny of embryoid in pepper anther culture].

Abstract

The characteristics of histology and cytology of embryogenesis in pepper anther culture were examined with fluorescence microscopy, scanning microscopy, and electron microscopy. Pepper was characterized by a strong asynchrony of pollen development within a single anther. With the change of culture period, the proportion of dead pollen increased drastically from 2 day after culture. Microspores that were cultured at the late-uninucleate stage followed one of two developmental pathways. In the more common route, the first sporophytic division was asymmetric and produced what appeared to be typical bicellular pollen. Embryogenic pollen was formed by repeated divisions of the vegetative nuclei. An exine with its specific pattern had already been formed, when microspores were released from tetrads. During subsequent pollen development, microspores increased in size and continued to strengthen the exine. After 24 h in culture, the microspores had increased in size. Thereafter, embryogenesis was indicated in some microspores by two different morphological changes. One featured an expansion in volume of the cell cluster around the germination aperture, the other showed cell cluster volume expansion over the entire microspore surface. Morphogenesis of microspore-derived embryos has been analyzed, at both light and electron microscopical levels. The changes in cell organization after embryogenesis induction, and the characterization of the time sequence of a set of structural events, had been also explained. These changes mainly affected the plastids, the vacuolar compartment, the cell wall and the nucleus. Further differentiation processes mimicked that of the zygotic development.