A new interpretation of meiotic prophase in lycopersicon esculentum (tomato)

Abstract

1. Meiotic prophase in the tomato was studied through the use of longitudinal anther sections. The existence of a maturity gradient through each pollen sac was established and the proper sequence of meiotic prophase stages determined. 2. After pachynema the homologous arms separate; the centromeres, and frequently the telomeres, remain paired. The stage has traditionally been interpreted as zygonema occuring before pachynema. It is suggested that this stage be referred to as schizonema. 3. Progressive separation causes the nucleus to become filled with strands. The stage is referred to as diffuse stage. During diffuse stage the centromeres become separated. 4. The individual bivalents become discernible again as diplotene chromosomes, the centromeres are separated and the homologous arms are held together at points of contact. Diakinesis follows. 5. Normal pachynema, the stage during which the chromosomes spread easily and therefore preferred for cytological studies, is preceded, for a considerable length of time, by cells which have tightly-bunched pachytene (paired) chromosomes. These cells are preceded by very early pollen mother cells which have interphase nuclei. 6. Evidence is presented that the sequence interphase — pachynema — schizonema — diffuse stage — diplonema — diakinesis exists in some other plants as well. 7. It is suggested that synapsis is complete in interphase, prossibly prior to duplication. If a similarity exists to Neurospora meiotic prophase, it may be that the telophase chromosomes of the premeiotic mitosis synapse and then elongate.