Chloroplast division machinery in higher plant

-The relation between PD ring and FtsZ ring-

Abstract

Summary: As chloroplasts(plastid)increase by binary fission, the understanding of the division machinery of the chloroplast is an important theme. Previously we reported on the chloroplast division apparatus, which consists of inner and outer double or triple rings(PD rings). Chloroplasts are assumed to arise from bacterial endosymbionts, while bacterial division is instigated by a bacterial cytokinesis Z ring protein(FtsZ). Here we present immuno-fluorescent and electron microscopic evidence of chloroplast division via complex machinery involving the FtsZ and PD rings in the higher plant Pelargonium zonale Ait. Prior to invagination, the FtsZ protein was attached to a ring at the stromal division site. Following formation of the FtsZ ring, the inner stromal and outer cytosolic PD rings appeared, signifying the initiation of invagination. The FtsZ ring and the PD rings were found at the leading edge of chloroplast constriction throughout division. During chloroplast division, neither the FtsZ nor the inner rings changed width, but the volume of the outer ring gradually increased. We suggest that the FtsZ ring determines the division region, after which the inner and outer PD rings are formed as a lining for the FtsZ ring. With the outerring providing the motivating force, the FtsZ and inner PD rings ultimately decompose to their base components.