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Plant function and evolutionary biology
RESEARCH ARTICLE

Involvement of Plasmalemmasomes and Carbonic Anhydrase in Photosynthetic Utilization of Bicarbonate in Chara corallina

G.D Price, M.R Badger, M.E Bassett and M.I Whitecross

Australian Journal of Plant Physiology 12(3) 241 - 256
Published: 1985

Abstract

There is a clear relationship between the density of plasmalemmasomes (PLSs) in the acid band regions of whorl cells of Chara corallina and the capacity of these cells to utilize HCO*¯/3 for photosynthesis. For cells grown in alkaline media, high PLS densities on the plasmalemma (50-85% coverage) were always correlated with high rates of HCO*¯/3 dependent O2 evolution (pH 9.3), reaching rates of 17-23 mol O2 mg Chl-¹ h-¹ at 5 mM inorganic carbon concentration. In alkaline culture, development of high PLS densities and high rates of HCO*¯/3 usage were related to provision of limiting levels of CO2 (< 12 M) in the media. High growth levels of CO2 (267 M) markedly reduced PLS densities and rates of HCO*¯/3 usage. Bicarbonate dependent O2 evolution (pH 9.3) was extremely sensitive to the carbonic anhydrase inhibitor ethoxyzolamide (20 M), whilst CO2-dependent O2 evolution (pH 5.5) was insensitive. Carbonic anhydrase (CA) activity was present in homogenates and in intact cells, suggesting that a periplasmic location is possible. It seems reasonable to suggest that, for Chara corallina, high PLS densities and CA activity are required for efficient utilization of HCO*¯/3 at alkaline pH. Plasmalemmasomes may be part of the HCO*¯/3-utilizing mechanism by acting as sites for localized pH generation, thus facilitating HCO*¯/3 utilization by either H+/HCO*¯/3 active cotransport or CA and pH-mediated external conversion of HCO*¯/3 to CO2 in the periplast.

https://doi.org/10.1071/PP9850241

© CSIRO 1985

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