Search

No Abstract

No Abstract

N. Orologas, S.G. Delivopoulos, A. Dimopoulou andI. Tsekos. 2005. Effects of 2,6-dichlorobenzonitrile on plasma membrane cellulose synthesizing complexes and cellulose localization in cells of the red alga Erythrocladia subintegra. Phycologia44: 465–476.The effects of 2,6-dichlorobenzonitrile (DCB), a cellulose biosynthesis inhibitor, on the density (number/μm2), the terminal complex (TC) length, the number of transverse rows of TC subunits of cellulose synthesizing linear TCs, the cellulose microfibril width and the structure and morphology of cell wall and colonies of Erythrocladia subintegrawere investigated. Treatment with 50 μM of DCB caused a partial inhibition of cellulose synthesis, whereas with higher concentrations (75–100 μM) no TCs were observed; this shows that DCB at these concentrations inhibits cellulose synthesis completely. The cellulose synthesis inhibition had a direct impact on the morphology of cells and colonies as well as on the cell wall structure and function. Ultrathin sections of E. subintegrafixed cells, when treated with cellobiohydrolase I (CBH I)–colloidal gold complex (10 nm gold particles), showed significant gold particle labelling on the cellulose microfibrils. In order to better visualize the inhibitory effect of DCB on cellulose synthesis, a combination of DCB and CBH I–gold complex treatment was applied. DCB treatment with increasing concentration (50, 75 and 100 μM) resulted in a gradual decreasing of the enzyme–gold labelling.

AbstractAs shown by freeze-fracture electron microscopy, the linear terminal complexes (TCs) in Erythrocladia subintegraRosenvinge, Erythrotrichia carnea(Dillwyn) J. Agardh, Porphyra leucostictaThuret, and Porphyra yezoensisUeda typically have regularly spaced rows of particles aligned transverse to the longitudinal axis of the TCs. The spacing between neighboring transverse particle rows is almost constant and ranges from 10.5 to 13.5 nm among the four species. The TC subunits appear to be interconnected by filament-like structures in transverse as well as longitudinal directions along the long axis of the TC. In the investigated species, both linear TCs and microfibrils are randomly distributed and the microfibrils show a flat, ribbon-like morphology. Isolated cellulose microfibrils in negatively stained preparations from Erythrocladiaand Porphyraappear as thin, ribbon-shaped structures, 1 to 1.5 nm thick (constant) and 5 to 70 nm wide (variable). It is proposed that each protein particle subunit in an ErythrocladiaTC synthesizes three glucan chains that are then assembled into a minisheet. Each transverse row of four TC subunits contributes to a fibrillar (minicrystal) component containing 12 glucan chains, with dimensions of 1.20 × 1.59 nm. The number of fibrillar (minicrystal) components assembled by a given TC and then laterally associated equals the number of transverse particle rows. The laterally associated minicrystal components contribute to the variation in microfibrillar width. The arrangement and consolidation of polymerases (cellulose synthase) and variation in their number in a single linear TC (Erythrocladia32 to 140 subunits, Erythrotrichia30 to 110, Porphyra yezoensis11 to 25, Porphyra leucosticta6 to 24) are responsible for the structure and flat, ribbon-like morphology of the microfibrils and for the variation in the width/diameter of the cellulose microfibrils. In red algae, cellulose occurs as highly oriented crystalline microfibrils.