Spatial distribution of functional OH− carriers along a characean internodal cell: Determined by the effect of cytochalasin B on H14CO 3 − assimilation
- 29 Downloads
The present study was aimed at testing an hypothesis relating to the OH− efflux pattern developed on internodal cells ofChara corallina. It was suggested that OH− efflux carriers were restricted to a limited number of sites along the internodal cell. Hydroxyl ions were considered to be delivered to these sites via the streaming cytoplasm. To test this hypothesis, cytochalasin B was used to inhibit cyclosis. Under these conditions OH− efflux and H14CO 3 − assimilation should have been inhibited.
Our results indicated that cyclosis was inhibited within 60 min in the presence of 30 μg/ml cytochalasin B. When14CO2 (pH 5.0) fixation experiments were conducted under these conditions, no inhibition of photosynthesis was observed. Cytochalasin B was shown, therefore, to inhibit cyclosis without affecting thein vivo reactions of photosynthesis.
A parallel study on the effect of increasing cytochalasin B concentrations on cyclosis and H14CO 3 − assimilation revealed that there was a limiting velocity of cyclosis below which H14CO 3 − assimilation was inhibited. These results were interpreted in terms of a rate-limiting step associated with the supply of OH− to the operational efflux sites.
At cytochalasin B concentrations below 15–20 μg/ml, no effect was observed on H14CO 3 − assimilation. This suggested that cytochalasin B does not interfere with the membrane-bound HCO 3 − and OH− transport systems of this species.
The OH− efflux pattern underwent significant modification following cyclosis inhibition. A change from discrete band efflux sites to a network of numerous small, localized, disc-shaped efflux sites was observed. The discovery of this modified OH− efflux system provided an explanation for the observed limited sensitivity of H14CO 3 − influx to cessation of cyclosis.
These results invalidated part of our hypothesis, since they revealed that the OH− carriers are uniformly distributed over the plasmalemma surface. A modified hypothesis to account for the spatial distribution of the OH− efflux sites is presented.
KeywordsHydroxyl Spatial Distribution Human Physiology Transport System Significant Modification
Unable to display preview. Download preview PDF.
- 5.Costerton, J.W.F., MacRobbie, E.A.C. 1970. Ultrastructure ofNitella translucens in relation to ion transport.J. Exp. Bot. 21:535Google Scholar
- 11.Lucas, W.J. 1975. Analysis of the diffusion symmetry developed by the alkaline and acid bands which form at the surface ofChara corallina cells.J. Exp. Bot. 26:271Google Scholar
- 12.Lucas, W.J. 1975. The influence of light intensity on the activation and operation of the hydroxyl efflux system ofChara corallina.J. Exp. Bot. 26:347Google Scholar
- 13.Lucas, W.J. 1975. Photosynthetic fixation of14carbon by internodal cells ofChara corallina.J. Exp. Bot. 26:331Google Scholar
- 14.Lucas, W.J. 1976. Plasmalemma transport of HCO3− and OH− inChara corallina: Nonantiporter systems.J. Exp. Bot. 27:19Google Scholar
- 15.Lucas, W.J., Smith, F.A. 1973. The formation of alkaline and acid regions at the surface ofChara corallina cells.J. Exp. Bot. 24:1Google Scholar
- 16.Lucas, W.J., Smith, F.A. 1976. Influence of irradiance on H+ efflux and Cl− influx inChara corallina: An investigation aimed at testing two Cl− transport models.Aust. J. Plant Physiol. 3:1Google Scholar
- 17.Sawa, T. 1974. New chromosome numbers for the genusTolypella (Characeae).Bull. Torrey Bot. Club 101:21Google Scholar
- 18.Sawa, T., Frame, P.W. 1974. Comparative anatomy of Charophyta: I. Oogonia and Oospores ofTolypella, with special references to the sterile Oogonial cell.Bull. Torrey Bot. Club 101:136Google Scholar
- 19.Smith, F.A. 1970. The mechanism of chloride transport in Characean cells.New Phytol. 69:903Google Scholar
- 24.Wood, R.D., Imahori, K. 1965. A revision of the Characeae, Part I. J. Cramer, WeinheimGoogle Scholar