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Plant Cell Advance Online Publication
Published on January 15, 2010; 10.1105/tpc.109.071084

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Received August 31, 2009
Returned for revision December 2, 2009
Accepted December 23, 2009

An Arabidopsis Mutant with High Cyclic Electron Flow around Photosystem I (hcef) Involving the NADPH Dehydrogenase Complex

Aaron K. Livingston 1, Jeffrey A. Cruz 1, Kaori Kohzuma 1, Amit Dhingra 2, and David M. Kramer 1*

1 Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340
2 Horticulture and Landscape Architecture, Washington State University, Pullman, Washington 99164-6340

* To whom correspondence should be addressed. E-mail: dkramer{at}wsu.edu.

Cyclic electron flow (CEFI) has been proposed to balance the chloroplast energy budget, but the pathway, mechanism, and physiological role remain unclear. We isolated a new class of mutant in Arabidopsis thaliana, hcef for high CEF1, which shows constitutively elevated CEF1. The first of these, hcef1, was mapped to chloroplast fructose-1,6-bisphosphatase. Crossing hcef1 with pgr5, which is deficient in the antimycin A–sensitive pathway for plastoquinone reduction, resulted in a double mutant that maintained the high CEF1 phenotype, implying that the PGR5-dependent pathway is not involved. By contrast, crossing hcef1 with crr2-2, deficient in thylakoid NADPH dehydrogenase (NDH) complex, results in a double mutant that is highly light sensitive and lacks elevated CEF1, suggesting that NDH plays a direct role in catalyzing or regulating CEF1. Additionally, the NdhI component of the NDH complex was highly expressed in hcef1, whereas other photosynthetic complexes, as well as PGR5, decreased. We propose that (1) NDH is specifically upregulated in hcef1, allowing for increased CEF1; (2) the hcef1 mutation imposes an elevated ATP demand that may trigger CEF1; and (3) alternative mechanisms for augmenting ATP cannot compensate for the loss of CEF1 through NDH.






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