Plant Physiol. Drug Metab Dispos
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Plant Physiology 75:146-150 (1984)
© 1984 American Society of Plant Biologists

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Reevaluation of the Role of Bicarbonate and Formate in the Regulation of Photosynthetic Electron Flow in Broken Chloroplasts

Jan F. H. Snel and Jack J. S. van Rensen

Laboratory of Plant Physiological Research, Gen. Foulkesweg 72, 6703 BW Wageningen, The Netherlands

The stimulation of the Hill reaction in CO2-depleted broken chloroplasts (Pisum sativum L. cv Rondo) by the total amount of dissolved CO2 and HCO3– (bicarbonate*) was measured at several formate concentrations. Formate appears to be a competitive inhibitor of the bicarbonate* stimulation of electron flow. From these experiments we have obtained a reactivation constant (Kr) of 78 ± 31 micromolar NaHCO3 and an inhibition constant (Ki) of 2.0 ± 0.7 millimolar HCOONa at pH 6.5. In the absence of formate, significant electron flow was measured at a bicarbonate* concentration well below Kr, suggesting that electron flow from Q, the primary electron acceptor of photosystem II, to plastoquinone can proceed when no bicarbonate* is bound to the regulatory site at the QB-protein. If so, bicarbonate* stimulation of electron flow is mainly a diminution of the inhibition of electron flow by formate. In view of the results, it is proposed that regulation of linear electron flow by bicarbonate* and formate is a mechanism that could link cell metabolism to photosynthetic electron flow.




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S. I. Allakhverdiev, I. Yruela, R. Picorel, and V. V. Klimov
Bicarbonate is an essential constituent of the water-oxidizing complex of photosystem II
PNAS, May 13, 1997; 94(10): 5050 - 5054.
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Copyright © 1984 by the American Society of Plant Biologists