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Plant and Cell Physiology Advance Access published online on January 31, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcj010
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Plant and Cell Physiology 2006 © The Japanese Society of Plant Physiologists (JSPP); all rights reserved.
Received December 19, 2005
Accepted January 16, 2006

Regular Paper

Compensation for Photosystem II Photoinactivation by Regulated Non-Photochemical Dissipation Influences the Impact of Photoinactivation on Electron Transport and CO2 Assimilation

Dmytro Kornyeyev 1, Barry A. Logan 2, David T. Tissue 3, Randy D. Allen 3, and A. Scott Holaday 3 *

1 Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA; Institute of Plant Physiology and Genetics, Vasylkivska St. 31/17, 03022, Kyiv, Ukraine
2 Department of Biology, Bowdoin College, Brunswick, ME 04011, USA
3 Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA

* To whom correspondence should be addressed.
A. Scott Holaday, E-mail: scott.holaday{at}ttu.edu


  Abstract

The extent to which photosystem (PS) II photoinactivation affects electron transport ({Phi}PSII) and CO2 assimilation remains controversial, in part, because it frequently occurs alongside inactivation of other components of photosynthesis, such as PSI. By manipulating conditions (darkness versus low light) after a high light/low temperature treatment, we examined the influence of different levels of PSII inactivation at the same level of PSI inactivation on {Phi}PSII and CO2 assimilation for Arabidopsis. Furthermore, we compared {Phi}PSII at high light and optimum temperature for wildtype Arabidopsis and a mutant (npq4-1) with impaired capacities for energy dissipation. Levels of PSII inactivation typical of natural conditions (less than 50%) were not associated with decreases in {Phi}PSII and CO2 assimilation at photon flux densities (PFD) above 150 µmol m-2 s-1. At higher PFDs, the light energy being absorbed was in excess of the energy that could be utilised by downstream processes. Arabidopsis plants downregulate PSII activity to dissipate such excess in accordance with the level of PSII photoinactivation that also serves to dissipate absorbed energy. Therefore, the overall levels of non-photochemical dissipation and the efficiency of photochemistry were not affected by PSII inactivation at high PFD. Under low PFD conditions, such compensation is not necessary, because the amount of light energy absorbed is not in excess of that needed for photochemistry and inactive PSII complexes are dissipating energy. We conclude that moderate photoinactivation of PSII complexes will only affect plant performance when periods of high PFD are followed by periods of low PFD.

Keywords: electron transport; photosystem II; photoinactivation; Arabidopsis; non-photochemical dissipation.
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