Morphological and quantitative changes in the population of cell organelles during microsporogenesis of Pinus sylvestris L. III. Morphological changes during the tetrad stage and in the young microspore. A quantitative approach to the changes in the population of cell organelles

A description and discussion are given of the morphological changes of the cell organelles during the middle and late tetrad stage and the young microspore of Pinus sylvestris with special reference to the pollen wall formation. In the middle tetrad stage the template of the pollen wall pattern appears to be the result of Golgi material excretion and callose wall formation. The fine fibrillar material from the content of the Golgi vesicles, consisting partly of a polysaccharide, forms the primesexine. During the late tetrad stage the sporopollenin originates from the microspore and is deposited on membranes mainly outside the cell. It penetrates into the primesexine. The starch in the plastids disappears and the lipid granules become voluminous; both elements are related to the pollen wall formation. The swelling of the sacci may be an osmotic process. From the quantitative approach it appears, that the young microspore contains approximately one fourth of the number of cell organelles present in the cell during zygotene. The cell organelle population probably does not change in number during the meiotic stages. A general survey summarizes the whole process of microsporogenesis till the young microspore stage. The control of pollen wall formation is also discussed.