Wound-healing in Vaucheria longicaulis Hoppaugh var. macounii Blum.

2. Cytoplasmic streaming and organdie movement

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SUMMARY

Differential interference contrast microscopy of the cytoplasm of Vaucheria longicaulis Hoppaugh var. macounii Blum reveals the presence of cable-like strands (tracks). The cytoplasmic tracks are orientated parallel to the length of the filament, and the organelles are closely associated and appear to move along them. Nuclei, mitochondria and Rhodamine B-positive bodies (RBIs) interact with a single track. Chloroplasts are closely associated with several tracks, although preferential association with one of the tracks is clearly observed. In uncut filaments, the different classes of organelles move independently of one another and travel at different speeds. Chloroplasts, mitochondria, RBIs, and smaller inclusions (SSIs) exhibit a bulk pattern of motion characterized by brief reversals in their primary pattern of movement that do not affect their final direction of travel. Nuclei move independently of each other and do not reverse their direction of movement. In cut filaments, cytoplasmic track density and relationship to organelles in the wound region during stage 1 is similar to that in uncut filaments. The cytoplasmic tracks extend into the wound-healing vesicle cytoplasm. Mitochondria and similarly-sized organelles move rapidly (in bulk) toward the wound site and into the wound-healing vesicle. In stage 2, an increase in cytoplasmic track density is observed in the wound region, and bulk movement of mitochondria and RBIs occurs toward the wound site. Nuclei also move in bulk, unidirectionally toward the wound. Organelle retraction from the wound is restricted to the chloroplasts.

Both uncut and cut filaments were treated with the cytoskeleton depolymerizers Cytochalasin B and Oryzalin to determine the role(s) of microfilaments and microtubules respectively in organelle movement and the overall role of the cytoskeleton in the wound-healing process. In uncut filaments, cytoplasmic streaming is severely reduced by both Cytochalasin B and Oryzalin, with the greatest reduction observed following cytochalasin B treatment. In cut filaments Cytochalasin B shows a greater effect on chloroplasts, mitochondria, and RBIs behaviour, while Oryzalin preferentially affects the nuclei. The results indicate that the bulk movement of chloroplasts, mitochondria and RBIs in uncut filaments may be microfilament-based, and the movement of nuclei microtubule-based.

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