The intracellular distribution of mass during ontogeny of pollen in Tradescantia L

Abstract

1. 1. Changes in the distribution of intracellular mass during ontogeny of pollen grains, as recorded by the application of Engström's X-ray absorption technique, are reported for the first time. 2. 2. During development of the mature pollen grain the greatest relative mass is associated with the chromosomes early in the process (pachytene through metaphase I). 3. 3. The extranuclear portions of the cells attain absorption (mass) characteristics similar to those of early prophase I chromosomes beginning approximately at late anaphase I—early telophase I. 4. 4. Cytokinesis, at telophase I and II, is strikingly associated with sharply localized heavy X-ray absorption in the newly-formed cell walls. 5. 5. By the end of telophase II, each microsporocyte has produced four microspores whose distinctive vacuome is recorded by minimal X-ray absorption. 6. 6. In the microspore, and particularly in the vegetative (tube) nucleus of the early binucleate pollen grain, the nucleolus becomes distinctly differentiated from the remainder of the nuclear structures by its comparatively intense X-ray absorption. 7. 7. During the later phases of ontogeny of the pollen grain, there appears to be a gradual increase in mass (X-ray absorption) in the cytoplasm. 8. 8. In the mature binucleate pollen grain high X-ray absorption is associated with extranuclear structure (cytoplasm and cell wall). Minimal absorption is recorded at this stage in both of the nuclei. 9. 9. Specific difficulties encountered in investigating microsporocyte (pollenmother-cell) material with this X-ray technique are briefly reviewed.