A transthylakoid proton gradient and inhibitors induce a non-photochemical fluorescence quenching in unicellular algae Nannochloropsis sp.

Non-photochemical quenching (NPQ) of chlorophyll fluorescence is thought to be an indicator of an essential regulation and photoprotection mechanism against high-light stress in photosynthetic organisms. In this report, special chemicals were used to perturb the kinetics of the ΔpH build-up and the xanthophyll cycle (XC) in Nannochloropsis sp. We found that NPQ was stimulated rapidly on exposure to high light and relaxed rapidly in darkness. The ΔpH could be obligatory for NPQ and ΔpH alone was not sufficient to induce NPQ. The XC, being strictly mediated by ΔpH, was also essential for NPQ. The results demonstrate that the mechanism of NPQ in Nannochloropsis sp. resembled that of diatoms.

► NPQ was stimulated rapidly in actinic light and promptly relaxed in the dark.
► The ΔpH could be obligatory for NPQ in Nannochloropsis sp.
► The xanthophylls, being strictly mediated by the ΔpH, are essential for NPQ.
► There may be protonable LHCSR-like proteins contributing to NPQ in Nannochloropsis sp.
► The mechanism of NPQ in Nannochloropsis sp. resembled that of diatoms.