REGULATION OF R-PROTEIN AND ENDONUCLEASE ACTIVITIES IN MEIOCYTES BY HOMOLOGOUS CHROMOSOME-PAIRING

Achiasmate meiocytes of Lilium cv. Black Beauty do not undergo DNA nicking at pachytene, nor do they acquire the high level of R-protein during zygotene-pachytene that is characteristic of chiasmate types. Induction of tetraploidy in such meiocytes with its accompanying increase in chiasma frequency results in a pachytene nicking pattern that is indistinguishable from what occurs in chiasmate plants. R-protein also increases to a level that on a per diploid genome basis is at least as high, and probably higher, than the level of chiasmate diploids. The absence of nicking in the achiasmate diploid is not due to a lack of appropriate enzyme activity but seems to result from the fact that unpaired or ineffectively paired chromosome regions are not accessible to the enzyme. The regulation of R-protein level by homologous pairing is examined but remains poorly understood. © 1979 Springer-Verlag.