. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 186 T. A. McCONNAUGHEY AND R. H. FALK Connaughey, in prep). Since HCO3 is more abundant in alkaline solutions, its unimportance in calcification suggests that the calcifying region can be fairly isolated from solution. The calcifying cell must therefore supply calcium, and remove the protons generated by the reaction Ca2+ + CO2 + H2O = CaCO3 + 2H+. And finally, Ca2+ is well known to affect characean photosynthesis and membrane properties associated with pH banding (, Lucas, 1976; Wiesenseel and Ruppert, 1977; Luhring and
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 186 T. A. McCONNAUGHEY AND R. H. FALK Connaughey, in prep). Since HCO3 is more abundant in alkaline solutions, its unimportance in calcification suggests that the calcifying region can be fairly isolated from solution. The calcifying cell must therefore supply calcium, and remove the protons generated by the reaction Ca2+ + CO2 + H2O = CaCO3 + 2H+. And finally, Ca2+ is well known to affect characean photosynthesis and membrane properties associated with pH banding (, Lucas, 1976; Wiesenseel and Ruppert, 1977; Luhring and Tazawa, 1985; Bisson, 1984; Tazawa el a/.. 1987). A Ca:+ ATPase model and a more conventional proton channel model for characean calcification are illustrated in Figure 1. Both models are elaborated to fit the available data. Ca2+ influx into the cell, in the Ca:+ ATPase model, occurs within the alkaline band (Fig. Ib) to produce the observed electrogenic character of pH banding (Walker and Smith, 1977). Figure Ic, e shows the use of molecular COi from the plant as the major carbon source for cal- cification (McConnaughey, in prep.) and the accretion of extracellular calcium deposits from the inside (demon- strated here). Figures Id and Ifdepict non-calcifying con- ditions, such as when Ca2+ or carbon levels are too low to sustain much CaCO^ precipitation. The non-calcifying condition can be experimentally useful, because the H+ fluxes measured extracellularly then reflect cellular H + transport most closely. The energy (E) required for proton uptake under both models is given by: E = FV(aZCa - bZH) + RT In (Ca,/Cat,)a/(H,/H0)b (1) The terms on the right represent work done against the membrane electrical potential V, and against the mem- brane chemical gradients. F is the Faraday constant, "a" and "b" are the numbers of Ca2i and H+ ions transported per cycle, Z is ionic charge. R is the gas constant, and T is Kelvin temperature. Cytoplasmic and external Ca
Size: 1688px × 1480px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
