The trade-off between the light-harvesting and photoprotectivefunctions of fucoxanthin-chlorophyll proteins dominates lightacclimation in Emiliania huxleyi (clone CCMP 1516)

摘要

Mechanistic understanding of the costs and benefits of photoacclimation requires knowledgeof how photophysiology is affected by changes in the molecular structure of the chloroplast. We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemicalquenching and PSII photoinactivation arises from changes in the abundancesof chloroplast proteins in Emiliania huxleyi strain CCMP 1516 grown at 30 (Low Light; LL)and 1000 (High Light; HL) lmol photons m~(-2)s~(-1) photon flux densities. Carbon-specific light-saturated gross photosynthesis rates were not significantly differentbetween cells acclimated to LL and HL. Acclimation to LL benefited cells by increasing biomass-specific light absorption and gross photosynthesis rates under low light, whereas acclimationto HL benefited cells by reducing the rate of photoinactivation of PSII under high light.Differences in the relative abundances of proteins assigned to light-harvesting (Lhcf), photoprotection(LI818-like), and the photosystem II (PSII) core complex accompanied differencesin photophysiology: specifically, Lhcf:PSII was greater under LL, whereas LI818:PSII wasgreater in HL. Thus, photoacclimation in E. huxleyi involved a trade-off amongst the characteristics oflight absorption and photoprotection, which could be attributed to changes in the abundanceand composition of proteins in the light-harvesting antenna of PSII.