DIVISION APPARATUS OF THE CHLOROPLAST IN NANNOCHLORIS BACILLARIS (CHLOROPHYTA)¹

Abstract

Chloroplast division in Nannochloris bacillaris Naumann (Chlorophyta) was examined by electron microscopy after preparation of samples by freeze‐substitution. A pair of belts appeared on the surface of the outer and inner envelope membranes at the middle of the chloroplast. These belts seemed to be constructed of thin fibrils that run parallel to the longitudinal direction of the belts. The outer fibrillar belt increased in width as the constriction of the chloroplast advanced. It appears that the fibrillar belt is the division apparatus of the chloroplast. It encircles the chloroplast and finally divides the chloroplast in two as the diameter of the belt decreases.

Novel Filaments 5 nm in Diameter Constitute the Cytosolic Ring of the Plastid Division Apparatus

“…This finding suggests that the filament itself does not have the ability to adhere directly to the outer envelope and that some linker proteins probably bind the bundle of filaments to the outer envelope specifically at the division site. In the green algae Nannochloris bacillaris (Ogawa et al, 1995) and Trebouxia potteri (Chida and Ueda, 1991), the outer PD ring appeared as a bundle of filaments in tangential sections, suggesting that our finding in Rhodophyta is probably applicable to Chlorophyta as well.Although no protein has been localized to the PD ring, FtsZ has been proposed as a candidate. On the basis of molecular genetic studies in Arabidopsis , it is hypothesized that chloroplast-targeted and nontargeted forms of FtsZs are components of the inner and outer PD rings, respectively (Osteryoung and Pyke, 1998;Erickson, 2000;Margolin, 2000;Osteryoung, 2000).…”

“…This finding suggests that the filament itself does not have the ability to adhere directly to the outer envelope and that some linker proteins probably bind the bundle of filaments to the outer envelope specifically at the division site. In the green algae Nannochloris bacillaris (Ogawa et al, 1995) and Trebouxia potteri (Chida and Ueda, 1991), the outer PD ring appeared as a bundle of filaments in tangential sections, suggesting that our finding in Rhodophyta is probably applicable to Chlorophyta as well.…”

“…In contrast, the outer rings remain in the cytosol after chloroplast division (Miyagishima et al, 2001). Some of these morphological changes have been reported in Chlorophyta (Chida and Ueda, 1991;Ogawa et al, 1995). The differences among the three rings suggest that the protein compositions of the rings are different (Miyagishima et al, 2001).…”

“…It has been detected in several species of Chlorophyta (green algae and terrestrial plants) (Hashimoto, 1986; Tewinkel and Volkmann, 1987;Hashimoto and Possingham, 1989;Oross and Possingham, 1989; Chida and Ueda, 1991;Duckett and Ligrone, 1993a, 1993b;Ogawa et al, 1995;Robertson et al, 1996), Rhodophyta (Mita et al, 1986;Suzuki et al, 1994), and Chromophyta (Hashimoto, 1997; Beech and Gilson, 2000) and is thought to be ubiquitous in the plant kingdom (summarized in Kuroiwa, 1998;Kuroiwa et al, 1998). In most organisms, the PD ring consists of a double ring structure, with one ring on the cytosolic face of the outer envelope (outer ring) and one on the stromal face of the inner envelope (inner ring).…”

Chloroplast Division and Differentially Regulated Expression of <i>FtsZ1</i> and <i>FtsZ2</i> in the Synchronous Culture of <i>Nannochloris bacillaris</i> (Chlorophyta, Trebouxiophyceae)

“…N. bacillaris has minimal cellular organization, consisting of 1 chloroplast and 1 mitochondrion, and divides by binary fission (Ogawa et al 1995, Arai et al 1998). NbFtsZ1 and NbFtsZ2, which belong to the FtsZ1 and FtsZ2 families, respectively, have been identified in N. bacillaris, and both NtFtsZ genes rescue ftsZ deficiency in E. coli (Koide et al 2004).…”