. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 190 T. A. McCONNAUGHEY AND R. H. FALK. Proton cycling involves calcium Low Ca2+ concentrations inhibit photosynthesis (Fig. 5, inset). This inhibition appears to involve Ca2+ fluxes, because plants incubated at the same low Ca2+ activity show more photosynthesis if additional buffered Ca2+ is added to solution (Table I). The rate of photosynthesis and the stimulation by buffered Ca2+ are greater with cal- cified than with decalcified plants (two way ANOVA, both factors and interactions significant at P HI o EC HI U 3 - UJ O
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 190 T. A. McCONNAUGHEY AND R. H. FALK. Proton cycling involves calcium Low Ca2+ concentrations inhibit photosynthesis (Fig. 5, inset). This inhibition appears to involve Ca2+ fluxes, because plants incubated at the same low Ca2+ activity show more photosynthesis if additional buffered Ca2+ is added to solution (Table I). The rate of photosynthesis and the stimulation by buffered Ca2+ are greater with cal- cified than with decalcified plants (two way ANOVA, both factors and interactions significant at P HI o EC HI U 3 - UJ O |.H O. Solution Unbuffered Buffered Change Calcified Decalcified ± ± ± ± +26% + 18% KILOSECONDS Figure 6. Inhibition of proton influx by La3t and Gd'*, measured with a vibrating proton specific electrode. Ordinate: voltage difference registered by the electrode between the extremes of its 10 micron excursion perpendicular to the cell. Inset: apparent proton influx calculated from a diffusion model, as a function of pH at the probe, for a signal of 1 mV over an excursion of 10 microns. Fluxes scale almost linearly with ex- cursion and voltage. diving conditions. The Ca2+ ATPase model also predicts localized Ca:+ efflux, which, in principle, should be de- tectable with Ca2+ specific microelectrodes. This efflux might be difficult to detect, however. It may occur un- derneath CaCO3 crystals or within an endomembrane system, and calcification may consume it before it is de- tected externally. More importantly, Ca2+ influx and efflux must both occur within the alkaline band to produce its electrogenic character (Fig. Ib), regionally cancelling the Ca2+ efflux signal. Therefore, detection requires a local asymmetry between Ca2+ influx and efflux under non- calcifying conditions (Fig. If). Such conditions encourage CaCO, dissolution and Ca2+ leaching from the cell wall. The resulting increase in peri- cellular Ca2+ concentration may be confused
Size: 2148px × 1163px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
