SUMMARY The sequence of events leading to wound‐healing and resumption of growth are studied by light microscopy including the use of differential interference contrast optics in Vaucheria longicaulis Hoppaugh var. macounii Blum. Wound‐healing has been divided into four stages. In stage 1, a wound‐healing vesicle is rapidly extruded from the wound site. Loss of turgor pressure, as observed by the appearance of plasmolysis, is seen along the length of the filament. In stage 2, the wound‐healing vesicle is sealed‐off from the filament. Organelles then accumulate at the barrier created by the sealing‐off process. This is followed by chloroplast retraction from and return to the wound site, concurrent with the restoration of turgor pressure in late stage 2. In stage 3 chloroplasts again retract from and return to the wound site, in preparation for stage 4 that finally leads to the resumption of growth on the part of the healed filament. The effect of wound healing on organelle distribution has been studied with the use of selective fiuorochromes. The distribution of nuclei, identified by DAPI staining, remains largely unchanged after wounding. Mitochondria and probable lipid bodies (designated RBIs) are identified by staining with DiOC6 and Rhodamine B, respectively. Their presence in the wound‐healing vesicle cytoplasm and accumulation along the wound site points to the existence of an efficient mechanism of ATP synthesis in support of the energy requirements associated with the healing process. CTC fluorescence along the wound site and wound vesicle cytoplasm suggests that Ca2+‐based exocytosis is important in both wound‐healing vesicle expansion and its sealing‐off from the filament.

SUMMARYDifferential 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.

No abstract