Differentiation of the tapetum in A vena II. the endoplasmic reticulum and golgi apparatus

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Abstract
During the differentiation of the tapetai cell the endoplasmic reticulum develops into an extensive, regionally differentiated system, consisting of 2 types of smooth cisternae interconnected by rough cisternae. Smooth cisternae with narrow lumens encircle the plastids and mitochondria and lead into rough cisternae with a wider lumen containing a moderately densely staining material. This material is stored in an unusual system of distended smooth cisternae, rather than being transferred to the Golgi apparatus. This system is believed to represent a holocrine secretion system, since it disappears at cell senescence at the same time as the pollen grains accumulate metabolite reserves. No morphological evidence could be found for the contribution of products of the reticulum to orbicule or sporopollenin synthesis. The dictyosomes and vesicles undergo a continuous series of changes as the tapetai cells differentiate. Development of flat dictyosome cisternae with dark amorphous contents is followed by a further change to more undulating, or curved cisternae. These different dictyosomes produce vesicles with morphologically distinct contents, some of which are observed fused with the plasma membrane. At maturity the vesicles form unique cylindrical channels, sometimes branched, which occur throughout the cytoplasm. Examination of thick sections by HVEM and STEM suggests that they are developed to facilitate movement of the dictyosome product through the masses of endoplasmic reticulum cisternae to the cell surface.