Desynapsis and the blockage of meiosis in Pennisetum orientale Rich.

Meiotic behaviour of a desynaptic plant of Pennisetum orientale Rich., which seems to have arisen through spontaneous gene mutation/s, is recorded. The plant showed an extremely rare type of desynapsis in which the precocious falling-apart of the homologous chromosomes was accompanied by the blockage of the meiotic course from metaphase I onwards. Different factors which may have led to the failure of chromosome synapsis and to the blockage of the meiotic division are discussed. The possibility of the participation of different enzymes in the initiation and continued progress of chromosome synapsis as well as for the different meiotic steps is considered. It has been inferred that the absence or later inactivation of these genetically-controlled enzymes might have resulted in the meiotic abnormalities observed in the present material. Another plausible regulatory mechanism based on the existence of a switch - through gene-repressing effect of histones - has been hypothesized and its possible evolutionary significance indicated.