Development of Nuclear Vacuoles in Sugar Beet Male Meiocytes

The formation, development and disappearance of nuclear vacuoles in three genetically different lines of Beta vulgaris L. are presented. Nuclear vacuoles may be generated in zygotene by the nuclear envelope, providing the membrane necessary for the formation of vacuoles within the nucleus. During subsequent stages of meiotic prophase nuclear vacuole volume increases rapidly, peaking in pachytene. In diplotene/diakinesis total nuclear vacuole volume falls gradually, and vacuoles eventually disappear in metaphase I. Maximum nuclear vacuole size in pachytene coincides with a notable increase in nuclear surface. We therefore suggest that nuclear vacuoles do not perform a mechanical function in the contraction of the karyoplasm, but instead act as compartments in which products of nuclear metabolism may be stored, and subsequently participate in the elimination of nuclear products to the cytoplasm. These processes may be related to changes occurring preparatory to the transition from sporophyte to gametophyte generation.