Photochemical and Nonphotochemical Fluorescence Quenching Processes in the Diatom Phaeodactylum tricornutum

Abstract

Nonphotochemical fluorescence quenching was found to exist in the dark-adapted state in the diatom Pbaeodactyhm tricornutum. Pretreatment of cells with the uncoupler carbonylcyanide mchlorophenylhydrazone (CCCP) or with nigericin resulted in increases in dark-adapted minimum and maximum fluorescence yields. This suggests that a pH gradient exists across the thylakoid membrane in the dark, which serves to quench fluorescence levels nonphotochemically. The physiological processes involved in establishing this proton gradient were sensitive to anaerobiosis and antimycin A. Based on these results, it is likely that this energization of the thylakoid membrane is due in part to chlororespiration, which involves oxygen-dependent electron flow through the plastoquinone pool. Chlororespiration has been shown previously to occur in diatoms. In addition, we observed that cells treated with 3-(3,4-dichlorophenyI)-l,l-dimethylurea exhibited very strong nonphotochemical quenching when illuminated with actinic light.The rate and extent of this quenching were light-intensity dependent. This quenching was reversed upon addition of CCCP or nigericin and was thus due primarily to the establishment of a pH gradient across the thylakoid membrane. Preincubation of cells with CCCP or nigericin or antimycin A completely abolished this quenching. Cyclic electron transport processes around photosystem I may be involved in establishing this proton gradient across the thylakoid membrane under conditions where linear electron transport is inhibited. At steady state under normal physiological conditions, the qualitative changes in photochemical and nonphotochemical fluorescence quenching at increasing photon flux densities were similar to those in higher plants. However, important quantitative differences existed at limiting and saturating intensities. Dissimilarities in the factors that regulate fluorescence quenching mechanisms in these organisms may account for these differences.One process that competes directly with photochemistry for deactivation of excited-state energy is fluorescence emission from Chl a molecules of the PSII antenna. Changes in the proportion of excited states utilized for photochemistry will result in changes in fluorescence intensity. In recent years, it has been shown that both photochemical and nonphotochemical processes reduce the yield of fluorescence during photosynthesis (Krause et al., 1982). However, our current knowledge of these processes is based primarily on studies with higher plants and green algae. The components involved in qP are present in the PSII reaction center, which has been found to be highly conserved throughout evolution (Thornber, 1986). It is therefore likely that the mechanism of photochemical quenching has also been conserved. In contrast, a diverse group of underlying processes controls qN, whose primary site of action is thought to be in the lightharvesting antennae. With the extensive diversity in the composition of light-harvesting complexes among the algae, it is likely that the m...

Endogenous versus environmental control of vertical migration by intertidal benthic microalgae

“…The rapid and large increase of F v /F m to maximum (and thereafter virtually constant) values is consistent with the well-known dissipation of non-photochemical quenching (NPQ) induced by low light that can occur in diatoms after prolonged darkness (Arsalane et al, 1994;Olaizola et al, 1994;Muller et al, 2001;Jesus et al, 2006;Seroˆdio et al, 2006). NPQ induces a decrease in F v /F m and its build-up in diatoms in the dark has been attributed to processes leading to the formation of a proton gradient across the thylakoid membrane, probably chlororespiration (Ting & Owens, 1993;Jakob et al, 1999;Lavaud et al, 2002). The decrease in F v /F m that was observed as microalgae accumulated at the surface in the dark may be the result of the operation of chlororespiration as cells come in contact with atmospheric oxygen, or the manifestation of an endogenous physiological rhythm affecting the transthylakoid proton gradient (Seroˆdio et al, 2005).…”

The place of diatoms in the biofuels industry

“…State transitions increase photosynthetic efficiency, as has been demonstrated by mutants in this process, which have reduced capacity to make ATP via cyclic-photophosphorylation and have impaired growth [49]. No evidence for state transitions or a reaction centerbased quenching mechanism has been found in diatoms [50], yet they are inherently more efficient than chlorophytes in balancing photosynthetic electron flow [48]. Perhaps the lower efficiency of chlorophytes involves the need for physical movements of antenna proteins over 500 nm [49], as compared with localized quenching by additional xanthophyll as occurs in diatoms.…”

Use of in vivo chlorophyll a fluorescence to quantify short-term variations in the productive biomass of intertidal microphytobenthos

“…4). However, such variability is restricted to extreme situations leading to the inactivation of functional reaction centres, such as extreme temperatures, photoinhibiting irradiances or anaerobiosis (Büchel & Wilhelm 1993, Ting & Owens 1993. In particular, changes in a* 650 may occur as a result of relatively slow photoadaptative processes affecting pigmentation and chloroplast morphology (e.g.…”