Antagonist effect between violaxanthin and de-epoxidated pigments in nonphotochemical quenching induction in the qE deficient brown alga Macrocystis pyrifera.

Nonphotochemical quenching (NPQ) of Photosystem II fluorescence is one of the most important photoprotection responses of phototropic organisms. NPQ in Macrocystis pyrifera is unique since the fast induction of this response, the energy dependent quenching (qE), is not present in this alga. In contrast to higher plants, NPQ in this organism is much more strongly related to xanthophyll cycle (XC) pigment interconversion. Characterization of how NPQ is controlled when qE is not present is important as this might represent an ancient response to light stress. Here, we describe the influence of the XC pigment pool (ΣXC) size on NPQ induction in M. pyrifera. The sum of violaxanthin (Vx) plus antheraxanthin and zeaxanthin (Zx) represents the ΣXC. This pool was three-fold larger in blades collected at the surface of the water column (19molmol(-1) Chl a×100) than in blades collected at 6m depth. Maximum NPQ was not different in samples with a ΣXC higher than 12molmol(-1) Chl a×100; however, NPQ induction was faster in blades with a large ΣXC. The increase in the NPQ induction rate was associated with a faster Vx to Zx conversion. Further, we found that NPQ depends on the de-epoxidation state of the ΣXC, not on the absolute concentration of Zx and antheraxanthin. Thus, there was an antagonist effect between Vx and de-epoxidated xanthophylls for NPQ. These results indicate that in the absence of qE, a large ΣXC is needed in M. pyrifera to respond faster to light stress conditions.