The Transfer of Desoxyribose Nucleic Acid from the Tapetum to the Microsporocytes at the Onset of Meiosis

The tapetum of the anther secretes specific substances at definite stages of development of the enclosed sporogenous tissue, as well as nutrients for its growth and differentiation. Globules with chromatin-like staining properties form at the surface of the tapetal nuclei when the enclosed sporogenous ceils are in a late leptotene stage of meiosis. They are Feulgen-positive, indicating that they contain an appreciable amount of desoxyribose nucleic acid. The globules move from the nuclei to the inner faces of the cells, pass through the cell walls and migrate between the microspore mother cells. The nuclei of the microsporocytes move from a central position to a peripheral one. During the course of this shift in position the loosely paired and somewhat polarized chromosomes become oriented so that the centromeres are adjacent to that portion of the nuclear membrane which is in close contact with the cell wall. The chromatin-like bodies between the microsporocytes collect opposite the regions where the nuclear membranes and cell walls are in contact. Their contents move through the walls into the adjacent nuclei and become associated with the paired chromosomes, bringing them into a close relationship. The formation of such bodies in the tapetum, their movement into the locule and ultimately into the nuclei of the microsporocytes has been observed in 17 species of angiosperms. The presence of such bodies between the spore mother cells and in close association with their peripherally located nuclei was noted in an additional six species. Chromatin-like materials likewise move from the nucellar cells of the ovule to the megasporocyte at the onset of megasporogenesis in Lilium regale and L. martagon. Droplets of a waxy material are later synthesized in the cytoplasm of the tapetal cells. These are secreted into the locule where they contribute to the formation of the exine of the developing pollen grains.