Ultrastructural observations on anther tapetum development of freeze-fixed Ledebouria socialis Roth (Hyacinthaceae)

Abstract

The tapetal ultrastructure of high-pressure-frozen, freeze-substituted Ledebouria socialis Roth (Hyacinthaceae) is described from the tetrad stage up to microspore mitosis. Cytoplasmic degeneration of the tapeturn occurs after microspore mitosis. During the tetrad stage and the early free-microspore stage the tapetum cells appear to be meristematic; after callose dissolution they show an intense exocytosis of polysaccharides into the anther locule. Later, the tapetum cells are characterized by abundant endoplasmic reticulum (ER). Highly osmiophilic pollenkitt precursor substances accumulate within distinct, partly irregular shaped cytoplasmic domains (“osmiophilic bodies”), which are intimately associated with the ER. It remains to be verified whether or not these bodies are derived from the ER. Because of their preservation and staining patterns the contents of these bodies are tentatively interpreted as flavonoids, one of the main pollenkitt pigments in angiosperms. Apart from these pigment bodies, there exist four other kinds of lipophilic inclusion within the anther (cells). The general aspects of lipid preservation in freeze-substituted samples are discussed. Staining with hot alcoholic phosphotungstic acid yielded good contrast of the ER and other membranes, which are often difficult to visualize in freeze-substituted, resin-embedded samples.