Time-resolution of the Antheraxanthin- and ΔpH-dependent Chlorophyll a Fluorescence Components Associated with Photosystem II Energy Dissipation in Mantoniella squamata¶

Abstract

The electronic excited-state behavior of photosystem II (PSII) in Mantoniella squamata, as influenced by the xanthophyll cycle and the transthylakoid pH gradient (⌬pH), was examined in vivo. Mantoniella is distinguished from other photosynthetic organisms by two main features namely (1) a unique light-harvesting complex that serves both photosystems I (PSI) and II (PSII); and (2) a violaxanthin (V) cycle that undergoes only one de-epoxidation step in excess light to accumulate the monoepoxide antheraxanthin (A) as opposed to the epoxide-free zeaxanthin (Z). The cells were treated first with high light to induce the ⌬pH and A accumulation, followed by herbicide-induced closure of PSII traps and a chilling treatment, to sustain and stabilize the ⌬pH and nigericin-sensitive fluorescence level in the dark. De-epoxidation was controlled with subsaturating concentrations of dithiothreitol (DTT) and was 5-10 times more sensitive to DTT than higher plant thylakoids. The PSII energy dissipation involved two steps: (1) the pH activation of the xanthophyll binding site that was associated with a narrowing and slight attenuation of the main 2 ns (ns ‫؍‬ 10 Ϫ9 s) fluorescence lifetime distribution; and (2) the concentration-dependent binding of A to the activated binding site yielding a second distribution centered around 0.9 ns. Consistent with the model of Gilmore et al. (1998) (Biochemistry 37, 13 582-13 593), the fractional intensity of the 0.9 ns component depended almost entirely on the A concentration and correlated linearly with the decrease of the steady-state chlorophyll a fluorescence intensity.

Photosystem II and Pigment Dynamics among Ecotypes of the Green Alga Ostreococcus

“…Prasinophytes, however, show different NPQ and xanthophyll cycle properties. For example, the prasinophyte Mantoniella squamata can be distinguished from other photosynthetic organisms by a xanthophyll cycle that undergoes a single deepoxidation step under excess light, leading to the accumulation of monoepoxide xanthophyll antheraxanthin (Gilmore and Yamamoto, 2001). In this study, the slow kinetics of induction and relaxation make the sustained NPQs superficially look like the "q I " category of NPQ related to photoinhibition.…”

The cost of photoinhibition

“…It is also known that the green (ulvophycean) marine macroalga Chlorodesmis fastigiata lacks xanthophyll cycle activity despite living in a high irradiance environment (Franklin et al 1996, Franklin and Larkum 1997). Some green prasinophycean marine microalgae such as Mantoniella squamata only de‐epoxidise violaxanthin as far as antheraxanthin (Gilmore and Yamamoto 2001, Goss et al 1998). The organisms lacking xanthophyll cycles, and also those that have such cycles, operate a mechanism of non‐photochemical dissipation of excess excitation energy in PSII which, like xanthophyll cycles, involves a low pH in the intrathylakoid space (Goss and Jakob 2010).…”

PHOTOPHYSIOLOGICAL PROPERTIES OF THE MARINE PICOEUKARYOTE PICOCHLORUM RCC 237 (TREBOUXIOPHYCEAE, CHLOROPHYTA)1

“…Accumulation of Zx or diatoxanthin is triggered by the formation of a pH gradient across the thylakoid membrane (Demming‐Adams and Adams 2000). Much attention has been paid to the photoprotection mechanism in chromophyte algae (Lavaud et al 2004, Harris et al 2005), while few studies have dealt with marine green microalgae (Gilmore and Yamamoto 2001, Garcia‐Mendoza et al 2002). The presumed minor contribution of green algae into the phytoplankton community, as well as the similarity of their xanthophyll cycle to the well‐documented one observed in terrestrial plants (Havaux and Niyogi 1999, Demming‐Adams and Adams 2000) makes the study of photoregulation in this group of low ecological interest.…”