PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Ultraviolet radiation affects xanthophylls cycle activity in the diatom Thalassiosira weissflogii. Ernesto Garcia-Mendoza^*,1, Nicole Dijkman², Rüdiger Röttgers ³, ¹ Departamento de Oceanografía Biológica/CICESE, Ensenada, Mexico² Centre for Estuarine and Marine Ecology/NIOO, Yerseke, The Netherlands³ Institute for Coastal Research/GKKS, Geesthacht, Germany

ABSTRACT- Ultraviolet radiation (UVR) has strong deleterious effects on biological systems. One of the most important physiological processes affected by UVR is photosynthesis. The RUV affects different components of the photosynthetic apparatus and enzymes involve in the photosynthetic dark reaction, but specifically photosystem II can be considered as the main target for damage. On the other hand, photosynthetically active radiation (PAR) in excess can produce also impairment of photosynthetic activity. Amongst other mechanisms, the xanthophyll cycle (XC) plays an important role in photoprotection against high light. The synthesis of zeaxanthin (or diatoxanthin in chromophytes)as a result of XC brings protection against excessive energy accumulation in the photosynthetic apparatus. Zeaxanthin protects via deactivation of excited chlorophyll a molecules or by promoting allosteric changes in PS II protein-pigment complexes that increases the quenching of energy. There is an extensive survey of the biochemical control and protective role of xanthophyll cycle to excess irradiance considering only PAR. However, in natural conditions, high irradiances may be accompanied by potentially damaging fluences of UVR (UVA+UVB). In the present work, we analyzed XC activity (reaction kinetics and related non-photochemical induction)in the marine diatom Thalassiosira weissflogii under natural and natural simulated conditions of UVR. It is reported that the protective reaction of the XC (synthesis of Diatoxanthin) is negatively affected when cells are exposed to high light in the presence of UVR. The consequences of this reduction is discussed in the view of short term exposures to HL together with UVR, and we postulate that reduction of the potential protective role of XC could be one of the main reasons for the impairment of photosynthesis activity under UVR.

KEY WORDS: photoinhibition, Xanthophyll cycle, Ultraviolet radiation, nonphotochemical quenching