Multiple FtsZ rings in a pleomorphic chloroplast in embryonic cap cells of Pelargonium zonale

Abstract

The behaviors of the chloroplast FtsZ ring and outer cytosolic and inner stromal plastid dividing rings (PD rings) of chloroplast division were investigated in the higher plant Pelargonium zonale using immuno-fluorescence and electron microscopy. For these studies, we used embryonic cap cells from early embryos, in which small chloroplasts duplicate by multiple fission of a pleomorphic chloroplast. FtsZ proteins were localized to several rings at future division sites preceding contraction. FtsZ rings were found at the leading edges of the chloroplast constriction sites throughout division. In contrast, the PD rings were observed at the constriction sites after the formation of the FtsZ rings. These observations demonstrate that FtsZ rings differ from PD rings, and indicate that the FtsZ ring determines the dividing plane before the initiation of chloroplast contraction and then, in concert with the PD rings, promotes chloroplast division.