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

Solving the molecular mechanisms of photoprotection in diatoms. Johann LAVAUD^*,,

ABSTRACT- Planktonic diatoms are ubiquitous marine photosynthetic micro-organisms of ecological importance. Because of water motions, diatoms have to cope with fluctuating light intensities. They periodically experience excess light exposures, when transported to the surface of the water column, that can lead to lethal photo-oxidative damages. To survive, they have evolved several photoprotective mechanisms, among which the dissipation of excess energy (or NPQ for 'non-photochemical chlorophyll fluorescence quenching') is considered as one of the most important mechanisms on a short time scale. This is an essential process that allows phytoplanktonic algae to maintain their capacity for primary production. In higher plants, where the NPQ mechanism elucidation is a longstanding topic of interest, several elements are necessary for the process, including a transthylakoid proton gradient, de-epoxidised forms of xanthophylls, and PsbS, a light-harvesting complex type protein. Although diatoms share with higher plants common components involved in NPQ, they show clear specific characteristics; especially PsbS does not exist and no orthologue of PsbS has yet been found. In diatoms, NPQ is larger and its development more rapid than in higher plants, partly due to the capacity of diatoms to accumulate very large amounts of xanthophylls in their light-harvesting complex. Understanding of the molecular mechanisms involved in NPQ process in diatoms is of first importance to elucidate the peculiar ecophysiology of diatoms and especially their high ability to adapt to changing environmental conditions. References for further reading: Lavaud et al., 2002, Plant Physiology, 129, 1398-1406/ Lavaud et al., 2002, Photosynthesis Research, 74, 51-59/ Lavaud et al., 2002, FEBS Letters, 523, 163-166/ Lavaud et al., 2003, Biochemistry, 42, 5802-5808/ Lavaud et al., 2004, Journal of Phycology, 40, 130-137/ Ruban, Lavaud et al., Photosynthesis research, in press.

KEY WORDS: Photoprotection, Diatoms, Non-photochemical chlorophyll fluorescence quenching, Xanthophyll cycle