Poster: Photosynthesis

Abs # 308: Site and mode of PsbS action in photosystem II revealed at 77K

Presenter:	Gilmore, Adam M, gilmore@rsbs.anu.edu.au
Authors	Gilmore, Adam M (A)   Li, Xiao-Ping  (B)   Niyogi, Krishna K (B)   Komura, Masayuki  (C)   Itoh, Shigeru  (C)
Affiliations:	(A): Ecosystem Dynamics Group, RSBS, IAS, Canberra, Australia (B): Dept. of Plant and Microbial Biology, U.C. Berkeley, Berkeley, CA, USA (C): Dept. of Physics, Nagoya Univ., Nagoya, Japan

Excess light-energy dissipation in Photosystem II (PSII) depends on xanthophyll carotenoids and lumen-pH-dependent protonation of the PsbS protein. The site and mode of PsbS action remain undetermined with respect to the peripheral versus the core-inner-antennae of PSII. In this study Arabidopsis chlorophyll b-less mutants lacking all peripheral antennae and most if not all minor chlorophyll a and b proteins of PSII were generated with varying doses of PsbS. The chlorophyll-b-less lines were compared to b-replete lines that also exhibited varying PsbS doses. PsbS-dependent energy dissipation induced at room-temperature was cryo-fixed at 77K. The flow of energy was measured and analyzed, respectively, using a streak-camera-spectrograph and double-convolution-integral method. The relative amplitudes of all PSII bands, including F680, F685 and F695 were systematically altered in a PsbS-dependent manner. The rapid F680 kinetics of peripheral antenna excitation transfer to the core-inner-antennae and the F685 band were mostly unaltered. The F695 band showed the major change as a strong, rapid energy dissipation mode. Similar changes with and without the peripheral antennae indicate a site of PsbS action near the core-inner-antennae and probably closely associated with CP47.