CYCLOHEXIMIDE-INDUCED NUCLEAR ALTERATIONS IN MAIZE ROOT TIPS

Abstract

Cycloheximide appears to act in G2 and also at the end of metaphase in disrupting the normal progression of chromosomes through the nuclear cycle in Zea mays L. A dose of 7.5 µg/ml resulted in the accumulation of metaphase figures at 60 min. Regardless of the length of treatment (60 or 120 min), a drop in mitotic index occurred after 60 min due to a decrease in the frequency of prophases. This reduction is attributed to a cycloheximide-sensitive transition point in G2 approximately 1 to 1.5 h before the start of mitosis. The incorporation of 14C-leucine into proteins was found to be inhibited by cycloheximide at concentrations ranging from 0.75 µg/ml (very slight inhibition) to 750 µg/ml (almost complete inhibition). Label incorporation into those proteins found in the nuclear fraction was inhibited sooner and to a lesser extent than into total proteins. Cycloheximide at 75.0 µg/ml induces a variety of cytogenetic variants of which nine classes were observed. These included alterations in both chromosome morphology and nuclear organization and occurred at frequencies significantly higher than the controls. The results suggest that cycloheximide can act at several levels of organization which together are essential for establishing and maintaining the events of the nuclear cycle.