SYNCHRONIZATION OF CHLOROPLAST DIVISION IN THE ULTRAMICROALGA CYANIDIOSCHYZON MEROLAE (RHODOPHYTA) BY TREATMENT WITH LIGHT AND APHIDICOLIN

A system of highly synchronized chloroplast divisions was developed in the unicellullar red alga Cyanidioschyzon merolae De Luca, Taddei, & Varano. Chloroplast divisions were examined by epifluorescence microsc opy following treatments with light and inhibitors. When the cells dur ing stationary phase were transferred into a new medium under a 12:12 h LD cycle, chloroplasts, mitochondria, and cell nuclei divided synchr onously in that order soon after the initiation of dark periods. More than 40% of the cells contained dividing chloroplasts. To obtain a sys tem of highly synchronized cell division and chloroplast division, the cells synchronized by a 12:12 h LD cycle were treated with various in hibitors. Nocodazole and propyzamide did not affect cell and organelle divisions, whereas aphidicolin markedly inhibited cell-nuclear divisi ons and cytokinesis and induced a delay in chloroplast division. More than 80% of the cells contained dividing chloroplasts when cells synch ronized by light were treated with aphidicolin for 12 h. This synchron ized system will be useful for studies of the molecular and cellular m echanisms of organelle divisions.