Rapid formation of antheraxanthin and zeaxanthin in seconds in microalgae and its relation to non-photochemical quenching.

The violaxanthin (V)-antheraxanthin (A)-zeaxanthin (Z) (VAZ) cycle was deemed a non-second-scale process of photoprotection in higher plants and microalgae, but the validity of this view has not been confirmed. To test this view, we explored responses of the VAZ cycle and the relationship between the VAZ cycle and non-photochemical quenching (NPQ) under highlight at second and minute scales in Heterosigma akashiwo and Platymonas sp. Both A and Z were generated in H. akashiwo during 15 s of light exposure, whereas only A rapidly accumulated within 15 s of exposure in Platymonas sp. The above results, together with a time-dependent sigmoidal relationship between the VAZ cycle (de-epoxidation state, A/Chl a, and Z/Chl a) and NPQ, proved that the VAZ cycle was a second-scale process related to NPQ. In addition, we found that not all NPQ was dependent on the VAZ cycle and suggested that NPQ model should be carefully modified due to the species-specific proportions of de-epoxidation-dependent NPQ.