Photoprotection in a monophyletic branch of chlorophyte algae is independent of energy‐dependent quenching (qE)

Abstract

Phototrophic organisms need to ensure high photosynthetic performance whilst suppressing reactive oxygen species (ROS)-induced stress occurring under excess light conditions. The xanthophyll cycle (XC), related to the high-energy quenching component (qE) of the nonphotochemical quenching (NPQ) of excitation energy, is considered to be an obligatory component of photoprotective mechanisms. The pigment composition of at least one representative of each major clade of Ulvophyceae (Chlorophyta) was investigated. We searched for a light-dependent conversion of pigments and investigated the NPQ capacity with regard to the contribution of XC and the qE component when grown under different light conditions. A XC was found to be absent in a monophyletic group of Ulvophyceae, the Bryopsidales, when cultivated under low light, but was triggered in one of the 10 investigated bryopsidalean species, Caulerpa cf. taxifolia, when cultivated under high light. Although Bryopsidales accumulate zeaxanthin (Zea) under high-light (HL) conditions, NPQ formation is independent of a XC and not related to qE. qE- and XC-independent NPQ in the Bryopsidales contradicts the common perception regarding its ubiquitous occurrence in Chloroplastida. Zea accumulation in HL-acclimated Bryopsidales most probably represents a remnant of a functional XC. The existence of a monophyletic algal taxon that lacks qE highlights the need for broad biodiversity studies on photoprotective mechanisms.

Diversity in Xanthophyll Cycle Pigments Content and Related Nonphotochemical Quenching (NPQ) Among Microalgae: Implications for Growth Strategy and Ecology

“…, Christa et al. ). In fact, in V‐containing microalgae, the NPQ mechanism appears very heterogeneous and can be achieved by different processes beyond the XC at the molecular level (reviewed in Finazzi and Minagawa ).…”

“…, Christa et al. , Berne et al. ), well illustrating the amazingly complex functional biodiversity of the XC‐NPQ process (Goss and Lepetit ).…”

“…, Christa et al. , Magdaong and Blankenship ) has strongly helped to better understand the physiological fundamentals of the xanthophyll cycle and related NPQ, particularly in plants and trees (Adams and Demmig‐Adams ). Photoautotrophs show great interspecific differences in XC pigment pool, de‐epoxidation state (DES = Dt/[Dt+Dd] or [Z+A]/[Z+A+V]) and related NPQ, partially because they experience different in situ growth environments (e.g., typically sun vs. shade acclimation in plants; Demmig‐Adams et al.…”

Photoprotective Non-photochemical Quenching Does Not Prevent Kleptoplasts From Net Photoinactivation

“…Understanding the basics of kleptoplast photophysiology is thus necessary to find factors that might be beneficial for an autonomous functioning of the photosynthetic apparatus (Handrich et al, 2017). Therefore, photoprotection mechanisms might be important to reduce PSII photoinactivation (Serôdio et al, 2014;Christa et al, 2017) and an active repair of damaged D1 would ensure continuing PSII activity (de Vries et al, 2013).…”

“…Many Sacoglossa feed on alga that lack important photoprotection mechanisms, such as the xanthophyll cycle (XC) and the q E part of NPQ (Cruz et al, 2015;Christa et al, 2017), and with regard to the kleptoplast longevity, there is no difference between the various retention forms since NR, StR and LtR forms feed on both types of algae and keep them for comparable starvation periods (Händeler et al, 2010;Christa et al, 2014b). The most prominent examples are Elysia chlorotica, which feeds on Vaucheria litorea, an alga that possess both mechanisms (Cruz et al, 2015), and Plakobranchus ocellatus, that consumes only XC and q E -deficient species (Maeda et al, 2012;Christa et al, 2013;Wade and Sherwood, 2018).…”