Poster: Photosynthesis

Abs # 349: Involvement of the xanthophyll cycle in the photosystem II damage and repair cycle in Dunaliella salina

Presenter:	Yokthongwattana, Kittisak , thylakoids@yahoo.com
Authors	Yokthongwattana, Kittisak  (A)   Jin, EonSeon  (A)   Polle, Juergen E.W. (B)   Melis, Anastasios  (A)
Affiliations:	(A): Department of Plant & Microbial Biology, 111 Koshland Hall, University of California, Berkeley CA 94720-3102 USA (B): Department of Biology, Brooklyn College, 2900 Bedford Ave, 200NE, Brooklyn, NY 11210 USA

The Dunaliella salina photosynthetic apparatus organization and function was investigated in wild type and a mutant (zea1) lacking all b,b-epoxycarotenoids derived from zeaxanthin. The zea1 mutant constitutively accumulated zeaxanthin under all growth conditions. In spite of the pronounced difference observed in the composition of b,b-epoxycarotenoids between wild type and zea1, no discernible difference could be observed between the two strains in terms of growth, photosynthesis, organization of the photosynthetic apparatus, photoacclimation, sensitivity to photodamage or recovery from photoinhibition. Wild type and zea1 were probed for the above parameters over a broad range of growth irradiance and upon light shift experiments (low-light to high-light shift and vice versa). A constitutive accumulation of zeaxanthin in the zea1 strain did not affect the acclimation of the photosynthetic apparatus to irradiance, as evidenced by indistinguishable irradiance-dependent adjustments in the chlorophyll antenna size and photosystem content of wild type and zea1 strain. Additionally, a constitutive accumulation of zeaxanthin in the zea1 strain did not affect rates of photodamage or the recovery of the photosynthetic apparatus from photoinhibition. However, zeaxanthin in the wild type accumulated in parallel with the accumulation of photodamaged PSII centers in the chloroplast thylakoids and decayed in tandem with a chloroplast recovery from photoinhibition. These results suggest a role for zeaxanthin in the protection of photodamaged and disassembled PSII reaction centers, apparently needed while PSII is in the process of degradation and replacement of the D1/32 kD reaction center protein.