On the origin of a slowly reversible fluorescence decay component in the Arabidopsis npq4 mutant

Abstract

Over-excitation of photosynthetic apparatus causing photoinhibition is counteracted by non-photochemical quenching (NPQ) of chlorophyll fluorescence, dissipating excess absorbed energy into heat. The PsbS protein plays a key role in this process, thus making the PsbS-less npq4 mutant unable to carry out qE, the major and most rapid component of NPQ. It was proposed that npq4 does perform qE-type quenching, although at lower rate than WT Arabidopsis. Here, we investigated the kinetics of NPQ in PsbS-depleted mutants of Arabidopsis. We show that red light was less effective than white light in decreasing maximal fluorescence in npq4 mutants. Also, the kinetics of fluorescence dark recovery included a decay component, qM, exhibiting the same amplitude and half-life in both WT and npq4 mutants. This component was uncouplersensitive and unaffected by photosystem II repair or mitochondrial ATP synthesis inhibitors. Targeted reverse genetic analysis showed that traits affecting composition of the photosynthetic apparatus, carotenoid biosynthesis and state transitions did not affect qM. This was depleted in the npq4phot2 mutant which is impaired in chloroplast photorelocation, implying that fluorescence decay, previously described as a quenching component in npq4 is, in fact, the result of decreased photon absorption caused by chloroplast relocation rather than a change in the activity of quenching reactions.

Photosynthesis under artificial light: the shift in primary and secondary metabolism

“…Some of these mechanisms are the specific topic of other papers included in this special issue (xanthophyll cycle [33], non-photochemical quenching [34], re-oxidation of the reduction equivalents through photorespiration, the malate valve and the action of antioxidants [35]). This section is dedicated to the metabolic shifts triggered by high light stress.…”

In Silico Analysis of the Regulation of the Photosynthetic Electron Transport Chain in C3 Plants

“…did not follow first-order kinetics). Although such kinetics are often explained as a sum of exponentials (Nilkens et al, 2010;Dall'Osto et al, 2014), a decomposition of qE into its components indicates that the direct contribution of PsbS + to qE had an "overshooting" behavior, whereas the contribution of ZX increased in a sigmoidal fashion (Fig. 6D).…”

“…The xanthophyll cycle, including regulation of violaxanthin de-epoxidase by lumen pH is included. Because of the importance of chloroplast movement in Arabidopsis (Kasahara et al, 2002;Dall'Osto et al, 2014), this process is also included, with expressions calibrated to published experiments (Davis and Hangarter, 2012;Łabuz et al, 2015), as described in the Supplementary Text. The model assumes a bifurcated reaction for the oxidation of PQH 2 at the oxidase site of cyt b 6 f (Kramer and Crofts, 1993), such that the Q cycle is always engaged (Sacksteder et al, 2000).…”

“…The study of NPQ in leaves makes use of measurements of chlorophyll fluorescence yield and lifetime (Nilkens et al, 2010;Dall'Osto et al, 2014;SylakGlassman et al, 2016). In plants, under many physiological conditions, NPQ is associated with the build-up of protonated PsbS (PsbS + ) and zeaxanthin (ZX), as regulated by lumen pH (Zaks et al, 2013;Horton, 2014), a process denoted as qE.…”

Changing the light environment: chloroplast signalling and response mechanisms

“…Ebenhö h et al [3] propose a mathematical model for relative contributions of non-photochemical quenching (NPQ) and state transition (ST) in light acclimation. The paper by Cazzaniga et al [4] identifies photoreceptor-dependent chloroplast movement as an additional pathway used to dissipate the excess absorbed energy, whereas Ruban & Belgio [5] investigate NPQ in relation to maximum light intensity tolerated by plants. Bertrand et al [6] investigate the different mechanisms involved in NPQ relaxation in diatoms.…”