1. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102, USA
2. Carnegie Institution of Washington, Department of Plant Biology, 260 Panama Street, Stanford, California 94305, USA
3. Umeå Plant Science Center, Department of Plant Physiology, University of Umeå, 901 87 Umeå, Sweden
4. Present address: Plant Biochemistry, University of Lund, PO Box 117, S-221 00 Lund, Sweden.

Correspondence to: Krishna K. Niyogi¹ Correspondence and requests for materials should be addressed to K.K.N. (e-mail: Email: niyogi@nature.berkeley.edu).

Abstract

Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO₂ results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules, thereby protecting the plant against photo-oxidative damage. To identify specific proteins that are involved in nonphotochemical quenching, we have isolated mutants of Arabidopsis thaliana that cannot dissipate excess absorbed light energy. Here we show that the gene encoding PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis. These results indicate that PsbS may be the site for nonphotochemical quenching, a finding that has implications for the functional evolution of pigment-binding proteins.

1. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102, USA
2. Carnegie Institution of Washington, Department of Plant Biology, 260 Panama Street, Stanford, California 94305, USA
3. Umeå Plant Science Center, Department of Plant Physiology, University of Umeå, 901 87 Umeå, Sweden
4. Present address: Plant Biochemistry, University of Lund, PO Box 117, S-221 00 Lund, Sweden.

Correspondence to: Krishna K. Niyogi¹ Correspondence and requests for materials should be addressed to K.K.N. (e-mail: Email: niyogi@nature.berkeley.edu).