Morphological changes in the tapetal cell during microsporogenesis of Pinus sylvestris L.

After zygotene the tapetal cell becomes osmiophilic. The electron density of the cytoplasm decreases during the early tetrad stage and increases afterwards. During the young microspore stage the tapetal cell degenerates. The electron density of the cytoplasm is caused mainly by the high content of ribosomes. From interphase II onwards the tapetal cell starts to produce sporopollenin. In the cytoplasm pro-orbicular bodies are found. The formation of orbicules seems connected with the endoplasmic reticulum and ribosomes. Outside the cell the sporopollenin appears around the orbicules and as a pollen sac against the cell wall of the endothecium cells. The electron dense globules on the plasma membrane may be related to the formation of sporopollenin.