| Abstract: | The formation of chlortetracycline (CTC)-induced wall appositions or plugs in internodal cells of Nitella flexilis (L.) Ag. was studied with light, fluorescence and electron microscopy. These plugs contain callose and pectin. A few minutes after CTC addition plug formation starts by fusion of polysaccharide-containing vesicles (glycosomes) with the plasmalemma. Plug growth is continued by incorporation of glycosome-endoplasmic reticulum (ER) complexes. The cytoplasm near the plug appears dense because of the accumulation of glycosomes and the increased electron density of plasma matrix and organelles. About 1 h after CTC addition plug growth ceases, the cytoplasm recovers to its pretreatment appearance, and a few glycosomes fuse singly with the plug membrane. Crystalline inclusions which consist of hexagonally packed rods are found near the plug. Coated vesicles and coated pits are clearly seen only in very early and late stages of plug formation. Callose is also found in parts of wound plugs produced after mechanical injury. No callose is present in the underlying, highly ordered wound wall. The failure to produce a wound wall beneath CTC-induced plugs appears to be related to the lower number of coated vesicles during plug formation. The possible significance of the partially coated reticulum in plug and wound wall formation is discussed. |
