SHORT‐TERM RESPONSE OF THE DIADINOXANTHIN CYCLE AND FLUORESCENCE YIELD TO HIGH IRRADIANCE IN CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)¹

Abstract

The relationship between the diadinoxanthin cycle and changes in fluorescence yield in the diatom Chaetoceros muelleri Lemm. (clone CH10, Amorient Aquafarm, Inc., Hawaii) was investigated. High‐light‐induced changes in fluorescence yield and xanthophyll de‐epoxidation occurred very rapidly (first order rate constant 1.60 min−1). The observed light‐induced changes in diatoxanthin and diadinoxanthin concentration were consistent with a two‐pool scheme for diadinoxanthin, one of which does not undergo de‐epoxidation. Changes in xanthophyll concentration correlated with changes in in vivo absorbance indicating that diadinoxanthin cycle activity in vivo can be monitored spectrophotometrically. However, changes in cell absorbance were small relative to total optical absorption cross section. Increases in the concentration of diatoxanthin were linearly correlated with increases in the rate constant for thermal de‐excitation in the antenna of photosystem II (PSII). Antenna quenching produced or mediated by diatoxanthin may, thus, protect the PSII reaction center in diatoms. Changes in the maximum fluorescence yield suggested that changes in the reaction center also contributed to nonphotochemical quenching of fluorescence. Thus, reaction center quenching affected the relationship between antenna quenching and changes in photochemical efficiency producing the effect of a decrease in fluorescence yield without a decrease in photochemical efficiency.

Limits to productivity of the algaPleurochrysis carterae(Haptophyta) grown in outdoor raceway ponds

“…Acclimation, as defined by Raven and Geider (2003), is the change of the macromolecular composition of an organism that occurs in response to variation of environmental conditions. Photoacclimation in free-living phytoplankton has been demonstrated in several studies (Brown and Richardson, 1968;Meeson and Sweeney, 1982;Olaizola and Yamamoto, 1994;Prezelin, 1976), however these studies have only measured photoacclimation over periods of less than 3 weeks whereas our results show that outdoor cultures of P. carterae take 4 weeks to photoacclimate fully. Several mechanisms are known to be involved in photoacclimation (Raven and Geider, 2003): (1) changes in the composition and cellular abundance of light-harvesting pigment-protein complexes, (2) changes in the abundance and ratios of PSI and PSII reaction centres and of other catalysts within the electron transport chain, (3) changes in the activity of CO 2 -fixing enzymes such as Rubisco and/or electron transport systems (Rivkin et al, 1982;Sukenik et al, 1987), and (4) changes in the content of photoprotective pigments (Macintyre et al, 2002).…”

Responses ofEmiliania huxleyi(Prymnesiophyceae) to step changes in photon flux density

“…First, DD is hypothesised to be a precursor in the biosynthesis of FUCO (Goericke & Welschmeyer, 1992b;Lohr & Wilhelm, 2001). Second, DD can be de-epoxidised to DT in the xanthophyll cycle Olaizola & Yamamoto, 1994). These two functions have opposite effects on light harvesting.…”

“…The other DD pool was hypothesised to serve as a precursor for FUCO synthesis. Data on the kinetics of DD and DT following step increases of PFD in diatoms also suggests that there are two DD pools (Willemoe¨s & Monas, 1991;Olaizola & Yamamoto, 1994). First, upon a shift to high light there is a rapid stoichiometric conversion of DD to DT that occurs within minutes.…”

Microphytobenthos Primary Production Estimated by Hyperspectral Reflectance

“…These indices were calculated using in vivo second derivative spectra absorption features and absorption properties previously published [15,[25][26][27].…”

“…DD 1 according to [25], DT 3 according to [15] ETR prediction following eq. 3 and 4, needed the estimation of LUE by radiometry (from eq.14), but also the optical absorption cross-section (a*) retrieved from the radiative transfer model MPBOM applied to each reflectance spectrum.…”