Identification of peroxisome-dividing ring in cyanidioschyzon merolae based on organelle partner hypothesis

Eukaryotic cells contain at least 3 types of double membrane-bound organelles (cell nucleus, mitochondrion and chloroplast (plastid), and 4 types of single membrane-bound organelles (endoplasmic reticulum (ER), Golgi apparatus, lysosome (vacuole) and peroxisome (microbody)). These membrane-bounded organelles cannot be formed de novo but are inherited by growth, division and separation during cell cycle. The double membrane-bounded organelle plays a role as a leading apparatus of the inheritance (division and separation) of the single membrane-bounded organelles. The cell-nucleus divides accompanied by ER and Golgi apparatus while the mitochondra divide accompanied by a peroxisome and lysosomes. Chloroplasts divide independently. In particular, although the peroxisome divides as an intimate partner of mitochondrial division, the peroxisome-dividing ring has not yet been observed at the division site by traditional electron microscopic fixation. So we examined the putative peroxisome-dividing ring in the primitive red alga Cyanidioschyzon merolae cells by use of chemical fixation and high pressure freeze fixation. We were able to identify an electron dense peroxisome-dividing ring at the division site by use of high pressure freeze fixation.