Author: Xu Shi-xiong, Zhu Cheng and Hu Shi-yi
J Integr Plant Biol 1990, 32 (11): -.
Changes in the organization of microtubules in Lilium during generative cell division and sperm formation were studied using in vitro grown pollen tubes and immunofluorescence techniques. In lily, 2--3 hours after polleff germination the generative cell following the vegetative nucleus enters the pollen tube. Once in the pollen tube the nucleus of the generative cell begins to elongate. The chromosomes inside the nucleus start to condense and the overall shape of the generative cell becomes spindle in shape. Due to the presence of strong background fluorescence induced during fixation, it is difficult to see clearly the pattern of distribution of the microtubules in most generative cells, especially, at the nucleus region. However, in those cells which do not show such strong background fluorescence, one can see that in the cytoplasm of the generative cell.there are a number of axially orientated microtubule fibers extending from one end of the cell to the other. Occasionally a few helically orientated microtubule fibers can also be seen outside the nucleus. But these helical fibers are never seen in the cytoplasm of the head and tail regions. During metaphase, all the chromosomes move towards the equatorial plate region and each chromosome appears to have an axially orientated microtubule fiber associated with it. When the fiber enters the equatorial plate region, the fiber is inter rupted by a dark spot. This dark interruption resembles closely the kinetochore region seen in Tradescantia virginiana. During anaphase, sister chromatids separate to opposite poles and two future nuclei will be formed. These two newly formed nuclei are still connected to each other by a number of microtubule fibers. Each fiber becomes much thickened when it enters the region where the original equatorial plate was situated. Thus at this region there is a very strongly fluorescent area. Thia strongly fluorescent area resembles closely the fluorescent 'bar' region due to microtubule overlapping and interdigitating seen in the dividing cells of the diatom, Stephanopyxis turris. During telophase, however, a opaque band begins to appear in the middle region of this strongly fluorescent area. According to our interpretation, this opaque band may represent the region of formation of the cell plate. As this interpretation is cor rect or not, we believe it can be resolved easily using either confocal laser scanning microscopy or electron microscopy. The pattern of distribution of the microtubules in the sperm is very similar to that seen in the generative cell. The sheets or bundles of microtubules seen by Derksen et al. in the generative cells of Lilium we suspect, could be artefacts due to background fluorescence.