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Can Parietin Transfer Energy Radiatively to Photosynthetic Pigments?

ABSTRACT: The main role of lichen anthraquinones is in protection against biotic and abiotic stresses, such as UV radiation. These compounds are frequently deposited as crystals outside the fungal hyphae and most of them emit visible fluorescence when excited by UV. We wondered whether the conversion of UV into visible fluorescence might be photosynthetically used by the photobiont, thereby converting UV into useful energy. To address this question, thalli of Xanthoria parietina were used as a model system. In this species the anthraquinone parietin accumulates in the outer upper cortex, conferring the species its characteristic yellow-orange colouration. In ethanol, parietin absorbed strongly in the blue and UV-B and emitted fluorescence in the range 480?540 nm, which partially matches with the absorption spectra of photosynthetic pigments. In intact thalli, it was determined by confocal microscopy that fluorescence emission spectra shifted 90 nm towards longer wavelengths. Then, to study energy transfer from parietin, we compared the response to UV of untreated and parietin-free thalli (removed with acetone). A chlorophyll fluorescence kinetic assessment provided evidence of UV-induced electron transport, though independently of the presence of parietin. Thus, a role for anthraquinones in energy harvesting is not supported for X. parietina under presented experimental conditions.

SUBMITTER: Fernandez-Marin B

PROVIDER: S-EPMC6099737 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Can Parietin Transfer Energy Radiatively to Photosynthetic Pigments?

Fernández-Marín Beatriz B Artetxe Unai U Becerril José María JM Martínez-Abaigar Javier J Núñez-Olivera Encarnación E García-Plazaola José Ignacio JI

Molecules (Basel, Switzerland) 20180717 7

The main role of lichen anthraquinones is in protection against biotic and abiotic stresses, such as UV radiation. These compounds are frequently deposited as crystals outside the fungal hyphae and most of them emit visible fluorescence when excited by UV. We wondered whether the conversion of UV into visible fluorescence might be photosynthetically used by the photobiont, thereby converting UV into useful energy. To address this question, thalli of <i>Xanthoria parietina</i> were used as a mode ...[more]

PMID: 30018202

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Project description:BackgroundPhotosynthetic pigments participating in the absorption, transformation and transfer of light energy play a very important role in plant growth. While, the spatial distribution of foliar pigments is an important indicator of environmental stress, such as pests, diseases and heavy metal stress.ResultsIn this paper, in situ quantitative visualization of chlorophyll and carotenoid was realized by combining the Raman spectroscopy with calibration model transfer, and a laboratory Raman spectral model was successfully extended to a portable field spectral measurement. Firstly, a nondestructive and fast model for determination of chlorophyll and carotenoid in tea leaf was established based on confocal micro-Raman spectrometer in the laboratory. Then the spectral model was extended to a real-time foliar map scanning spectra of a field portable Raman spectrometer through calibration model transfer, and the spectral variation between the confocal micro-Raman spectrometer in the laboratory and the portable Raman spectrometer were effectively corrected by the direct standardization (DS) algorithm. The portable map scanning Raman spectra of the tea leaves after the model transfer were got into the established quantitative determination model to predict the concentration of photosynthetic pigments at each pixel of the tea leaves. The predicted photosynthetic pigments concentration of each pixel was imaged to illustrate the distribution map of foliar pigments. Statistical analysis showed that the predicted pigment contents were highly correlated with the real contents.ConclusionsIt can be concluded that the Raman spectroscopy was applicable for in situ, non-destructive and rapid quantitative detecting and imaging of photosynthetic pigment concentration in tea leaves, and the spectral detection model established based on the laboratory Raman spectrometer can be applied to a portable field spectrometer for quantitatively imaging of the foliar pigments.

Project description:Steady-state and ultrafast time-resolved optical spectroscopic investigations have been carried out at 293 and 10 K on LH2 pigment-protein complexes isolated from three different strains of photosynthetic bacteria: Rhodobacter (Rb.) sphaeroides G1C, Rb. sphaeroides 2.4.1 (anaerobically and aerobically grown), and Rps. acidophila 10050. The LH2 complexes obtained from these strains contain the carotenoids, neurosporene, spheroidene, spheroidenone, and rhodopin glucoside, respectively. These molecules have a systematically increasing number of pi-electron conjugated carbon-carbon double bonds. Steady-state absorption and fluorescence excitation experiments have revealed that the total efficiency of energy transfer from the carotenoids to bacteriochlorophyll is independent of temperature and nearly constant at approximately 90% for the LH2 complexes containing neurosporene, spheroidene, spheroidenone, but drops to approximately 53% for the complex containing rhodopin glucoside. Ultrafast transient absorption spectra in the near-infrared (NIR) region of the purified carotenoids in solution have revealed the energies of the S1 (2(1)Ag-)-->S2 (1(1)Bu+) excited-state transitions which, when subtracted from the energies of the S0 (1(1)Ag-)-->S2 (1(1)Bu+) transitions determined by steady-state absorption measurements, give precise values for the positions of the S1 (2(1)Ag-) states of the carotenoids. Global fitting of the ultrafast spectral and temporal data sets have revealed the dynamics of the pathways of de-excitation of the carotenoid excited states. The pathways include energy transfer to bacteriochlorophyll, population of the so-called S* state of the carotenoids, and formation of carotenoid radical cations (Car*+). The investigation has found that excitation energy transfer to bacteriochlorophyll is partitioned through the S1 (1(1)Ag-), S2 (1(1)Bu+), and S* states of the different carotenoids to varying degrees. This is understood through a consideration of the energies of the states and the spectral profiles of the molecules. A significant finding is that, due to the low S1 (2(1)Ag-) energy of rhodopin glucoside, energy transfer from this state to the bacteriochlorophylls is significantly less probable compared to the other complexes. This work resolves a long-standing question regarding the cause of the precipitous drop in energy transfer efficiency when the extent of pi-electron conjugation of the carotenoid is extended from ten to eleven conjugated carbon-carbon double bonds in LH2 complexes from purple photosynthetic bacteria.

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Can Parietin Transfer Energy Radiatively to Photosynthetic Pigments?

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Can Parietin Transfer Energy Radiatively to Photosynthetic Pigments?

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