pheophytin-a and antheraxanthin

The ecological importance and diversity of pico/nanoplanktonic algae remains poorly studied in marine waters, in part because many are tiny and without distinctive morphological features. Amongst green algae, Mamiellophyceae such as Micromonas or Bathycoccus are dominant in coastal waters while prasinophytes clade VII, yet not formerly described, appear to be major players in open oceanic waters. The pigment composition of 14 strains representative of different subclades of clade VII was analyzed using a method that improves the separation of loroxanthin and neoxanthin. All the prasinophytes clade VII analyzed here showed a pigment composition similar to that previously reported for RCC287 corresponding to pigment group prasino-2A. However, we detected in addition astaxanthin for which it is the first report in prasinophytes. Among the strains analyzed, the pigment signature is qualitatively similar within subclades A and B. By contrast, RCC3402 from subclade C (Picocystis) lacks loroxanthin, astaxanthin, and antheraxanthin but contains alloxanthin, diatoxanthin, and monadoxanthin that are usually found in diatoms or cryptophytes. For subclades A and B, loroxanthin was lowest at highest light irradiance suggesting a light-harvesting role of this pigment in clade VII as in Tetraselmis.

Topics: Carotenoids; Chlorophyll; Chlorophyll A; Chlorophyta; Light; Lutein; Oceans and Seas; Photosynthesis; Pigments, Biological; Xanthophylls; Zeaxanthins

In the Crassulacean acid metabolism (CAM) plants Clusia alata Triana and Planch., decarboxylation of citrate during phase III of CAM took place later than malate decarboxylation. The interdependence of these two CO(2) and NADPH sources is discussed. High light accelerated malate decarboxylation during the day and lowered citrate levels. Strong light stress also activated mechanisms that can protect the plant against oxidative stress. Upon transfer from low light (200micromol m(-2)s(-1)) to high light (650-740micromol m(-2)s(-1)), after 2 days, there was a transient increase of non-photochemical quenching (NPQ) of fluorescence of chlorophyll a of photosystem II. This indicated acute photoinhibition, which declined again after 7 days of exposure. Conversely, after 1 week exposure to high light, the mechanisms of interconversion of violaxanthin (V), antheraxanthin (A), zeaxanthin (Z) (epoxydation/de-epoxydation) were activated. This was accompanied by an increase in pigment levels at dawn and dusk.

Topics: Adaptation, Physiological; Chlorophyll; Chlorophyll A; Citric Acid; Clusia; Decarboxylation; Fluorescence; Light; Malates; Photosynthesis; Photosystem II Protein Complex; Stress, Physiological; Xanthophylls; Zeaxanthins

Nonlinear regression analysis (NLR) is applied to quantify the dynamic response of non-photochemical fluorescence quenching (NPQ) of Trifolium repens cv. Regal upon dark to light transition. Commonly, only steady-state levels of NPQ are evaluated, ignoring transient kinetics. Experimental NPQ kinetics are fitted best with a sum of two functions: a sigmoidal Hill function plus a transient logarithmic normal function. It is shown that not only steady-state level of NPQ, but also the speed at which steady state is reached, increased with light intensity. The question is raised which biological processes cause the induction of the components of NPQ kinetics. The NPQ kinetics are found to resemble the kinetics of antheraxanthin and zeaxanthin formation during a dark to light transition. Furthermore, both molecules are known to induce NPQ. The hypothesis is put forward that a transient phase of NPQ (0-2 min after transition) is dependent upon concentrations of antheraxanthin, whereas the saturating phase corresponds with the production of zeaxanthin. A mathematical model, based on the presented hypothesis, predicts the effect of increasing light intensity on concentrations of antheraxanthin and zeaxanthin which correspond with experimental results. Implications of the hypothesis are discussed as well as the role of NLR in evaluating chlorophyll a fluorescence kinetics.

Topics: Adaptation, Ocular; beta Carotene; Chlorophyll; Chlorophyll A; Fluorescence; Models, Biological; Photosynthesis; Regression Analysis; Trifolium; Xanthophylls; Zeaxanthins

The electronic excited-state behavior of photosystem II (PSII) in Mantoniella squamata, as influenced by the xanthophyll cycle and the transthylakoid pH gradient (delta 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 delta pH and A accumulation, followed by herbicide-induced closure of PSII traps and a chilling treatment, to sustain and stabilize the delta 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(-9) 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 alpha fluorescence intensity.

Topics: Carotenoids; Chlorophyll; Chlorophyll A; Chlorophyta; Hydrogen-Ion Concentration; Light-Harvesting Protein Complexes; Photochemistry; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Xanthophylls

The xanthophyll cycle-dependent dissipation of excitation energy in higher plants is one of the most important regulatory and photoprotective mechanisms in photosynthesis. Using parallel time-resolved and pulse-amplitude modulation fluorometry, we studied the influence of the intrathylakoid pH and the xanthophyll cycle carotenoids on the PSII chlorophyll (Chl) a fluorescence yield in thylakoids of Arabidopsis, spinach, and barley. Increases in concentrations of dithiothreitol in thylakoids, which have a trans-thylakoid membrane pH gradient and are known to have decreased conversion of violaxanthin (V) to zeaxanthin (Z), lead to (1) decreases in the fractional intensity of the approximately 0.5 ns Chl a fluorescence lifetime (tau) distribution component and simultaneous increases in a 1.6-1.8 ns fluorescence component and (2) increases in the maximal fluorescence intensity. These effects disappear when the pH gradient is eliminated by the addition of nigericin. To quantitatively explain these results, we present a new mathematical model that describes the simultaneous effects of the chloroplast trans-thylakoid membrane pH gradient and xanthophyll cycle pigments on the PSII Chl a fluorescence tau distributions and intensity. The model assumes that (1) there exists a specific binding site for Z (or antheraxanthin, A) among or in an inner antenna complex (primarily CP29), (2) this binding site is activated by a low intrathylakoid pH (pK approximately 4.5) that increases the affinity for Z (or A), (3) about one Z or A molecule binds to the activated site, and (4) this binding effectively "switches" the fluorescence tau distribution of the PSII unit to a state with a decreased fluorescence tau and emission intensity (a "dimmer switch" concept). This binding is suggested to cause the formation of an exciton trap with a rapid intrinsic rate constant of heat dissipation. Statistical analysis of the data yields an equilibrium association constant, Ka, that ranges from 0.7 to 3.4 per PSII for the protonated/activated binding site for Z (or A). The model explains (1) the relative fraction of the approximately 0.5 ns fluorescence component as a function of both Z and A concentration and intrathylakoid pH, (2) the dependence of the ratio of F'm/Fm on the fraction of the 0.5 ns fluorescence tau component (where F'm and Fm are maximal fluorescence intensities in the presence and the absence of a pH gradient), and (3) the dependence of the ratio of F'm/Fm on the concentra

Topics: beta Carotene; Carotenoids; Chlorophyll; Chlorophyll A; Chloroplasts; Fluorescence Polarization; Hordeum; Hydrogen-Ion Concentration; Intracellular Membranes; Lutein; Photochemistry; Pigments, Biological; Spectrometry, Fluorescence; Spinacia oleracea; Xanthophylls; Zeaxanthins

The xanthophyll cycle apparently aids the photoprotection of photosystem II by regulating the nonradiative dissipation of excess absorbed light energy as heat. However, it is a controversial question whether the resulting nonphotochemical quenching is soley dependent on xanthophyll cycle activity or not. The xanthophyll cycle consists of two enzymic reactions, namely deepoxidation of the diepoxide violaxanthin to the epoxide-free zeaxanthin and the much slower, reverse process of epoxidation. While deepoxidation requires a transthylakoid pH gradient (delta pH), epoxidation can proceed irrespective of a delta pH. Herein, we compared the extent and kinetics of deepoxidation and epoxidation to the changes in fluorescence in the presence of a light-induced thylakoid delta pH. We show that epoxidation reverses fluorescence quenching without affecting thylakoid delta pH. These results suggest that epoxidase activity reverses quenching by removing deepoxidized xanthophyll cycle pigments from quenching complexes and converting them to a nonquenching form. The transmembrane organization of the xanthophyll cycle influences the localization and the availability of deepoxidized xanthophylls is to support nonphotochemical quenching capacity. The results confirm the view that rapidly reversible nonphotochemical quenching is dependent on deepoxidized xanthophyll.

Topics: beta Carotene; Carotenoids; Chlorophyll; Chlorophyll A; Chloroplasts; Epoxy Compounds; Hydrogen-Ion Concentration; Light-Harvesting Protein Complexes; Membrane Potentials; NADP; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Spectrometry, Fluorescence; Xanthophylls; Zeaxanthins