Abstract
We report on the changes the photosynthetic apparatus of Chlamydomonas reinhardtii undergoes upon acclimation to different light intensity. When grown in high light, cells had a faster growth rate and higher biomass production compared with low and control light conditions. However, cells acclimated to low light intensity are indeed able to produce more biomass per photon available as compared with high light-acclimated cells, which dissipate as heat a large part of light absorbed, thus reducing their photosynthetic efficiency. This dissipative state is strictly dependent on the accumulation of LhcSR3, a protein related to light-harvesting complexes, responsible for nonphotochemical quenching in microalgae. Other changes induced in the composition of the photosynthetic apparatus upon high light acclimation consist of an increase of carotenoid content on a chlorophyll basis, particularly zeaxanthin, and a major down-regulation of light absorption capacity by decreasing the chlorophyll content per cell. Surprisingly, the antenna size of both photosystem I and II is not modulated by acclimation; rather, the regulation affects the PSI/PSII ratio. Major effects of the acclimation to low light consist of increased activity of state 1 and 2 transitions and increased contributions of cyclic electron flow.
Highlights
Photosynthetic organisms deal with different irradiance conditions
Because we show that cyclic electron flow is reduced in high light (HL) acclimated cells versus low light (LL) and control light (CL) cells (Fig. 10), we tentatively suggest that Lhca4
C. reinhardtii cells acclimated to different light conditions are characterized by a reduction of pigment content per cells leading to a modulation of PSI and photosystem II (PSII) content
Summary
Photosynthetic organisms deal with different irradiance conditions. Results: In Chlamydomonas reinhardtii, acclimation to different irradiances of growth involves modulation of photosynthetic protein content per cell. Cells acclimated to low light intensity are able to produce more biomass per photon available as compared with high light-acclimated cells, which dissipate as heat a large part of light absorbed, reducing their photosynthetic efficiency This dissipative state is strictly dependent on the accumulation of LhcSR3, a protein related to light-harvesting complexes, responsible for nonphotochemical quenching in microalgae. We analyzed in detail the acclimatized response of C. reinhardtii cells to light intensity and observed that modulation of the relative abundance of Lhc proteins is restricted to minor component(s) of the antenna system, whereas bulk antenna subunits are constitutively expressed These results support the possibility of a genetically manipulated light-harvesting apparatus of C. reinhardtii for increased light use efficiency in photobioreactors
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