This Article Full Text Full Text (PDF) All Versions of this Article: 132/3/1464    most recent pp.102.018861v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (18) Citing Articles via Google Scholar Google Scholar Articles by Forti, G. Articles by Finazzi, G. Search for Related Content PubMed PubMed Citation Articles by Forti, G. Articles by Finazzi, G. Agricola Articles by Forti, G. Articles by Finazzi, G.

BIOENERGETICS AND PHOTOSYNTHESIS

In Vivo Changes of the Oxidation-Reduction State of NADP and of the ATP/ADP Cellular Ratio Linked to the Photosynthetic Activity in Chlamydomonas reinhardtii¹

Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Sezione di Milano, Dipartimento di Biologia dell'Università di Milano, Via Celoria 26, Milano 20133, Italy

The ATP/ADP and NADP/NADPH ratios have been measured in whole-cell extract of the green alga Chlamydomonas reinhardtii, to understand their availability for CO₂ assimilation by the Calvin cycle in vivo. Measurements were performed during the dark-light transition of both aerobic and anaerobic cells, under illumination with saturating or low light intensity. Two different patterns of behavior were observed: (a) In anaerobic cells, during the lag preceding O₂ evolution, ATP was synthesized without changes in the NADP/NADPH ratio, consistently with the operation of cyclic electron flow. (b) In aerobiosis, illumination increased the ATP/ADP ratio independently of the intensity used, whereas the amount of NADPH was decreased at limiting photon flux and regained the dark-adapted level under saturating photon flux. Moreover, under these conditions, the addition of low concentrations of uncouplers stimulated photosynthetic O₂ evolution. These observations suggest that the photosynthetic generation of reducing equivalents rather than the rate of ATP formation limits the photosynthetic assimilation of CO₂ in C. reinhardtii cells. This situation is peculiar to C. reinhardtii, because neither NADPH nor ATP limited this process in plant leaves, as shown by their increase upon illumination in barley (Hordeum vulgare) leaves, independent of light intensity. Experiments are presented and were designed to evaluate the contribution of different physiological processes that might increase the photosynthetic ATP/NADPH ratio—the Mehler reaction, respiratory ATP supply following the transfer of reducing equivalents via the malate/oxaloacetate shuttle, and cyclic electron flow around PSI—to this metabolic situation.

¹ This work was supported by the Consiglio Nazionale delle Ricerche of Italy.

² Present address: Unité Propre de Recherche 1261 Centre National de la Recherche Scientifique, 13 rue Pierre et Marie Curie, Paris, France.

^* Corresponding author; e-mail Giorgio.Forti{at}unimi.it; fax 39–02–5031–4813.

Received December 9, 2002; returned for revision January 15, 2003; accepted January 28, 2003.

This article has been cited by other articles:

				P. Cardol, J. Alric, J. Girard-Bascou, F. Franck, F.-A. Wollman, and G. Finazzi Impaired respiration discloses the physiological significance of state transitions in Chlamydomonas PNAS, September 15, 2009; 106(37): 15979 - 15984. [Abstract] [Full Text] [PDF]

				B. B. Fischer, M. Wiesendanger, and R. I. L. Eggen Growth Condition-Dependent Sensitivity, Photodamage and Stress Response of Chlamydomonas reinhardtii Exposed to High Light Conditions Plant Cell Physiol., August 1, 2006; 47(8): 1135 - 1145. [Abstract] [Full Text] [PDF]

				K.-i. Wakabayashi and S. M. King Modulation of Chlamydomonas reinhardtii flagellar motility by redox poise J. Cell Biol., June 5, 2006; 173(5): 743 - 754. [Abstract] [Full Text] [PDF]

				G. Forti and G. Caldiroli State Transitions in Chlamydomonas reinhardtii. The Role of the Mehler Reaction in State 2-to-State 1 Transition Plant Physiology, February 1, 2005; 137(2): 492 - 499. [Abstract] [Full Text] [PDF]

				D. Chamot, K. R. Colvin, S. L. Kujat-Choy, and G. W. Owttrim RNA Structural Rearrangement via Unwinding and Annealing by the Cyanobacterial RNA Helicase, CrhR J. Biol. Chem., January 21, 2005; 280(3): 2036 - 2044. [Abstract] [Full Text] [PDF]

				S. Esposito, G. Guerriero, V. Vona, V. Di Martino Rigano, S. Carfagna, and C. Rigano Glutamate synthase activities and protein changes in relation to nitrogen nutrition in barley: the dependence on different plastidic glucose-6P dehydrogenase isoforms J. Exp. Bot., January 1, 2005; 56(409): 55 - 64. [Abstract] [Full Text] [PDF]

				G. Finazzi The central role of the green alga Chlamydomonas reinhardtii in revealing the mechanism of state transitions J. Exp. Bot., January 1, 2005; 56(411): 383 - 388. [Abstract] [Full Text] [PDF]