Unravelling the different components of nonphotochemical quenching using a novel analytical pipeline

Summary

Photoprotection in plants includes processes collectively known as nonphotochemical quenching (NPQ), which quench excess excitation-energy in photosystem II. NPQ is triggered by acidification of the thylakoid lumen, which leads to PsbS-protein protonation and violaxanthin de-epoxidase activation, resulting in zeaxanthin accumulation. Despite extensive study, questions persist about the mechanisms of NPQ. We have set up a novel analytical pipeline to disentangle NPQ induction curves measured at many light intensities into a limited number of different kinetic components. To validate the method, we applied it to Chl-fluorescence measurements, which utilised the saturating-pulse methodology, on wild-type (wt) and zeaxanthin-lacking (npq1) Arabidopsis thaliana plants. NPQ induction curves in wt and npq1 can be explained by four components ((Formula presented.), (Formula presented.), (Formula presented.) and (Formula presented.)). The fastest two ((Formula presented.) and (Formula presented.)) correlate with pH difference formed across the thylakoid membrane in wt and npq1. In wt, the slower component ((Formula presented.)) appears to be due to the formation of zeaxanthin-related quenching whilst for npq1, this component is ‘replaced’ by a slower component ((Formula presented.)), which reflects a photoinhibition-like process that appears in the absence of zeaxanthin-induced quenching. Expanding this approach will allow the effects of mutations and other abiotic-stress factors to be directly probed by changes in these underlying components.