CYTOPLASMIC CHANNELS AND CHROMATIN MIGRATION IN MEIOCYTES OF ARNEBIA HISPIDISSIMA (SIEB) DC

Microsporogenesis was studied in Arnebia hispidissima which provided interesting evidence for the occurrence of cytoplasmic channels and DNA migration between the meiocytes. The intercommunicating channels (0.25-1.75 μ in diameter) are considered to be a prerequisite for chromatin migration and to act as pathways between the connected meiocytes. They may develop at any stage of meiosis from early prophase to metaphase II and the migration may take place at any time following channel formation. The tendency of chromatin to migrate seemed to be higher in the early prophasic stages when it moved in the form of ill-defined masses or clumps. The chances of migration as well as the amount of migrating chromatin is reduced as the meiosis advances. The amount of chromatin migrating varies from a small portion to the entire chromatin mass or nucleus. Pollen mother cells with double the normal amount of chromatin as well as those with little or none were studied as well as cells with increased or decreased chromosome numbers. In the chromatin mass, uni- or bivalents stretched between the meiocytes or attenuated towards the channel, were frequently seen. Occasional semi-asyndesis, multivalent formation, precocity, and nondisjunction was also noted.The possibility of channel formation and the induction of chromatin movement as a consequence of mechanical or procedural defect is ruled out. It is believed that these cytoplasmic channels have no relation with the plasmodesmata but they arise de novo and that chromatin migration occurs as a natural phenomenon (in some species). The observations are not due to faulty fixation, staining, or squashing. © 1969 OXFORD UNIVERSITY PRESS.