PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Non-photochemical quenching (qe) involves interaction of PsbS with the Photosystem II core antenna. Xiao-Ping Li^*,1, Adam Gilmore², Krishna Niyogi¹, ¹ Department of Plant and Microbial Biology, University of California, Berkeley, 111 Koshland Hall, Berkeley, CA, USA² Jobin-Yvon Inc., 3880 Park Ave, Edison, NJ, USA

ABSTRACT- The S subunit of photosystem II (PsbS) is a key element of excess energy dissipation in the photosynthetic apparatus. Through its two lumen-exposed glutamates, E122 and E226, PsbS senses lumen pH changes and regulates the xanthophyll-dependent de-excitation of chlorophyll when the absorbed light energy is excessive. Overexpression of PsbS in a triple mutant strain lacking chlorophyll b, Lhcb5, and the endogenous psbS gene showed that none of the six PS II light harvesting proteins (Lhcb1 to Lhcb6) is necessary for PsbS-mediated energy dissipation. Chlorophyll fluorescence lifetime measurements showed specific quenching of a fluorescence band at 695 nm that has been associated with the core antenna protein CP47. Results with single and double mutations of E122 and E226 have suggested a bifacial PsbS quenching model in which one of two functional halves of the PsbS protein must contact the PS II core antenna (most probably CP47) to allow for energy transfer from core antenna chlorophylls to pigments bound to PsbS. Data from F1 generation crosses have shown that non-functional PsbS competes with wild-type PsbS for functional association with PS II cores. These results support our proposed model that the energy dissipation occurs in PsbS that closely contacts the PS II core antenna.

KEY WORDS: non-photochemical quenching, psbs, qe