Polysome formation and incorporation of new ribosomes into polysomes during germination of the embryonic axis of maize

Abstract

Isolated axes of Zea mays L. cvs CiV 2 and CUZCO were imbibed for different periods of time, and free polysomes were extracted and analysed by centrifugation in a sucrose gradient. The amount of rRNA per axis was determined at different moments of germination. Polysome reassembly was practically completed by 8 h and 54% of the preformed ribosomes were found in the polysome fraction. An increase in the proportion of large polysomes was also observed during this period of germination. During the following period, the polysome content and the distribution of the various classes of polysomes remained unchanged. The time of appearance of newly synthesized ribosomes into the polysomes was investigated using axes germinated in the presence of [ 3 H]‐uridine. Centrifugal analysis of EDTA‐dissociated polysomes and gel electrophoretic analysis of polysomal RNA showed that new ribosomes appeared into polysomes a few hours after completion of the initial polysome assembly. When released into the cytoplasm, the new ribosomes were preferentially incorporated into polysomes rather than stored as free ribosomes.