Cytochemical and ultrastructural peculiarities of embryogenic pollen grains and of young androgenic embryos in Datura innoxia

Publisher Website
Google Scholar
Abstract
Cytochemical and ultrastructural studies of androgenic embryogenesis in Datura innoxia Mill. have been performed on (a) uncultured pollen grains collected at the stage favourable to embryo formation, i.e., at the time just before and just after the first haploid mitosis of the microspore nucleus (flower bud length of 4–5 cm); and (b) pollen grains and young androgenic embryos picked from the medium after 5, 9, and 11 days in culture.Only features presumed to play a role in the induction of androgenic embryogenesis are described.The phase of pollen development favourable to embryogenesis is very short but it involves important changes in the cytochemical features and in the ultrastructure of pollen grains. The changes are particularly clear in RNA and nucleohistone stainabilities and in the number and activity of the cytoplasmic organelles.It is suggested that it is not one particular metabolic or ultrastructural state of the cell which is responsible for the embryogenesis competence but that it is the fact that the changes occur which is important. Pollen which is in an unstable ultrastructural and metabolic state will be more sensitive to external stimuli.The study of very young androgenic embryos shows several features which are presumed to be responsible for the induction of embryogenesis: (a) Changes in cytoplasmic distribution and in nuclear organization consecutive to the first haploid mitosis in the microspore. These modifications sometimes lead to the formation of two equal pollen nuclei instead of differing vegetative and generative nuclei. The two identical nuclei are located in two equal-sized cells or in a single pollen cell. (b) Variations in pollen RNA content and in the organization of the endoplasmic reticulum which are related to changes in the pollen metabolism. (c) Modifications of the plasmalemma within pollen grains and of the cell wall surrounding the pollen grains. Such modifications are presumed to cause variations in the intercellular exchanges as well as in the exchanges between pollen and medium.

This publication has 0 references indexed in Scilit: