Ultrastructural and Cytochemical Evidence for the Presence of Peroxisomes in the Generative Cell of Magnolia × soulangeana Pollen Grain

Abstract

The generative cell (GC) development during three sequential stages of Magnolia × soulangeana pollen grain maturation was investigated by light and electron microscopy. Plastids were not identified in this cell but mitochondria, Golgi bodies and vesicles as well as rough endoplasmic reticulum profiles were always present. Microtubules were also present, their number increasing and their disposition varying during GC maturation. The most conspicuous components of the GC cytoplasm were the microbodies. The latter were few in number in the newly formed GC, and the appearance of their matrix was different from later developmental stages. A clear microbodial proliferation occurred in the GC during an intermediate stage of pollen maturation. Then, the microbody matrix was either fibrillar to granular as in the vegetative cell microbodies or very dense and compact. The polymorphism and size range and the frequent aggregation of these organelles in one or more clusters were also noteworthy. Tilting of semithin sections as well as the analysis of serial sections suggested that a number or enlarged and irregularly shaped microbodies co-exist with smaller and more spherical ones, the latter probably originating by budding. In the GC of the mature pollen the microbody-like organelles were in general more uniform both in shape and size. The cytochemical test of DAB was positive in the microbodies of both the pollen cells, thus demonstrating their peroxisomic nature. The function of the microbodies in the GC is not clear. In this cell, a few lipid droplets only exist during the first developmental stage and the microbodies were apparently unrelated to any other organelle. Possibly, these are unspecialized microbodies which are paternally transmitted, but it is not excluded that, temporarily, they may play some special role during GC maturation.