The mechanism of bicarbonate assimilation by the polar leaves of Potamogeton and Elodea. CO2 concentrations at the leaf surface |
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Authors: | H. B. A. PRINS J. F. H. SNEL P. E. ZANSTRA R. J. HELDER |
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Affiliation: | Department of Plant Physiology, University of Groningen, P.O. Box 14, 9750 AA Haren (Gn), The Netherlands |
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Abstract: | Abstract. Photosynthetic utilization of HCO, in leaves of Poiamogeton and Elodea occurs at the lower leaf side, with subsequent OH∼ release at the upper side. It is accompanied by transport of cations, in the present experiment K +, across the leaf. The resulting pH and K+ concentration changes near the leaf surface were recorded with miniature electrodes. From the pH and K+ concentration the concentrations of the different inorganic carbon species were calculated and compared with photosynthetic O, production. HCO−3 utilization is accompanied by a drastic increase in the free CO2 concentration near the lower epidermis. Experiments with CO2− and HCO3−free solutions showed an oscillating acidification near the lower epidermis and alkalinization near the upper epidermis. It is concluded that the acidification results from the activity of light-dependent H+ pumps. The finding that an increase in pH at the upper side always coincided with a decrease at the lower in these experiments shows that the H+ pumps and the OH− extruding mechanism are coupled although occurring in different cell layers. Previously we have suggested that the first step in the process of photosynthetic HCO3− utilization is external conversion of HCO3−" by acidification caused by light-dependent H+ pumps. The present results strongly support this hypothesis. Two possible pathways for the accompanying K + transport are discussed. The model presented here explains the known inhibiting effects of buffers and high pH on photosynlhetic HCO3− utilization. |
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Keywords: | Potatnogeton lucens Elodea canadensis photosynthesis aquatic ungiosperms bicarbonate carbon dioxide polar transport surface pH unstirred layer |
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