Acetabularia acetabulum displays specific patterns of calcification. Adult cells that are placed in media permissive for calcification begin calcifying at the rhizoid and the calcification thereafter proceeds up the stalk towards the apex. The apex is generally the last part of the cell to calcify. In addition, a small region of the stalk adjacent to the rhizoid frequently remains uncalcified. Models of algal calcification state that calcification arises when the cell creates an alkaline environment near the cell wall. I used the BRC facilities to identify the direction and location of proton fluxes at several points along Acetabularia cells. As expected, the majority of rhizoids tested showed proton influx (and resulting alkalinity in the media), which correlates with calcification initially appearing at the rhizoid. Also as expected, the majority of cells showed proton efflux (which would acidify the media immediately adjacent to the rhizoid, which correlates with the lack of calcification in that region. Surprisingly, however, the apex always showed a proton influx and media alkalinization, which was unexpected since the apex is normally the last region to calcify. The proton fluxes also show light dependent patterns. Turning the lights off and on induced specific changes in flux intensity and direction in different parts of the alga. Experiments with DCMU (an inhibitor of photosynthesis) suggested that the apical proton flux patterns may be linked to photosynthesis. The fluxes at the rhizoid and the region adjacent to the rhizoid did not showas clear an effect of DCMU, suggesting light/dark effects on the fluxes of these directions may have a photomorphogenetic component. This initial characterization suggests that calcification in Acetabularia is not simply the result of direction of proton flux but may in some way be inhibited along the younger, apical cell wall. These data also demonstrate a spatial separation of function (proton flux) within the Acetabularia cell and have provided the beginning for an exploration of the mechanism underlying calcification.
Showing the most recent 10 out of 144 publications
