Tapetal Ultrastructural Changes During Pollen Development. I. Studies onAntirrhinum Maius

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Abstract
Anther sections of Antirrhinum maius in various stages of development have been examined with the electron microscope and the ultrastructural modifications of the tapetal cells have been followed during the development of the pollen grains. Characteristic of the early stages of development is the presence of a great number of intensely proliferating Golgi bodies and of spherical bodies, located in the perinuclear space in proximity of the plasmalemma and in the endoplasmic reticulum. They are bounded by a single membrane on which ribosomes are regularly ranged facing the body cavity. Probably the bodies located in the perinuclear space play a role in the nuclear-cytoplasmic information exchanges, while those in connection with the endoplasmic reticulum seem to be simply related to an enhanced endoplasmic reticulum activity. In the late tetrad stage a second body population appears. These bodies are spherical, electrondense and without bounding membrane. They are located at the cell periphery towards the anther cavity near the plasma membrane; probably they are connected with the sporopollenin deposition. In the final stage of pollen development a large amount of grey bodies, generally lacking a bounding membrane, appears inside the tapetal cells, togheter with numerous proplastids, showing a dark and highly vesiculated matrix. Of particular interest seems the frequent close connection between the vesiculated proplastids and the grey bodies. It is supposed that the vesiculated proplastids contribute to the carotenoid increase in the grey bodies; probably the latter are responsible for the « Pollenkitt » formation around the differentiated pollen grains.