Search results for "PHOTOCHEMICAL"
showing 10 items of 108 documents
Linking photosynthesis and sun-induced fluorescence at sub-daily to seasonal scales
2018
Abstract Due to its close link to the photosynthetic process, sun-induced chlorophyll fluorescence (F) opens new possibilities to study dynamics of photosynthetic light reactions and to quantify CO2 assimilation rates. Although recent studies show that F is linearly related to gross primary production (GPP) on coarse spatial and temporal scales, it is argued that this relationship may be mainly driven by seasonal changes in absorbed photochemical active radiation (APAR) and less by the plant light use efficiency (LUE). In this work a high-resolution spectrometer was used to continuously measure red and far-red fluorescence and different reflectance indices within a sugar beet field during t…
Remote sensing of solar-induced chlorophyll fluorescence (SIF) in vegetation: 50 years of progress
2019
Remote sensing of solar-induced chlorophyll fluorescence (SIF) is a rapidly advancing front in terrestrial vegetation science, with emerging capability in space-based methodologies and diverse application prospects. Although remote sensing of SIF – especially from space – is seen as a contemporary new specialty for terrestrial plants, it is founded upon a multi-decadal history of research, applications, and sensor developments in active and passive sensing of chlorophyll fluorescence. Current technical capabilities allow SIF to be measured across a range of biological, spatial, and temporal scales. As an optical signal, SIF may be assessed remotely using high-resolution spectral sensors in …
Early Diagnosis of Vegetation Health From High-Resolution Hyperspectral and Thermal Imagery: Lessons Learned From Empirical Relationships and Radiati…
2019
[Purpose of Review] We provide a comprehensive review of the empirical and modelling approaches used to quantify the radiation–vegetation interactions related to vegetation temperature, leaf optical properties linked to pigment absorption and chlorophyll fluorescence emission, and of their capability to monitor vegetation health. Part 1 provides an overview of the main physiological indicators (PIs) applied in remote sensing to detect alterations in plant functioning linked to vegetation diseases and decline processes. Part 2 reviews the recent advances in the development of quantitative methods to assess PI through hyperspectral and thermal images.
In vivo photoprotection mechanisms observed from leaf spectral absorbance changes showing VIS–NIR slow-induced conformational pigment bed changes
2019
Abstract Regulated heat dissipation under excessive light comprises a complexity of mechanisms, whereby the supramolecular light-harvesting pigment–protein complex (LHC) shifts state from light harvesting towards heat dissipation, quenching the excess of photo-induced excitation energy in a non-photochemical way. Based on whole-leaf spectroscopy measuring upward and downward spectral radiance fluxes, we studied spectrally contiguous (hyperspectral) transient time series of absorbance A(λ,t) and passively induced chlorophyll fluorescence F(λ,t) dynamics of intact leaves in the visible and near-infrared wavelengths (VIS–NIR, 400–800 nm) after sudden strong natural-like illumination exposure. …
Photoprotection dynamics observed at leaf level from fast temporal reflectance changes
2018
Vegetation dynamically reacts to the available photosynthetically active radiation (PAR) by adjusting the photosynthetic apparatus to either a light harvesting or a photoprotective modus. When activating the photoprotection mechanism, either minor or major pigment-protein interactions may occur at the leaf level, resulting in different light absorption and consequently reflectance intensities. The reflectance changes were measured during sudden illumination transients designed to provoke fast adaptation to high irradiance. Different spectral reflectance change features were observed during different stages of photoprotection activation, extending over part of the visible spectral range (i.e…
Spatial Variation of Leaf Optical Properties in a Boreal Forest Is Influenced by Species and Light Environment
2017
Leaf Optical Properties (LOPs) convey information relating to temporally dynamic photosynthetic activity and biochemistry. LOPs are also sensitive to variability in anatomically related traits such as Specific Leaf Area (SLA), via the interplay of intra-leaf light scattering and absorption processes. Therefore, variability in such traits, which may demonstrate little plasticity over time, potentially disrupts remote sensing estimates of photosynthesis or biochemistry across space. To help to disentangle the various factors that contribute to the variability of LOPs, we defined baseline variation as variation in LOPs that occurs across space, but not time. Next we hypothesized that there wer…
Chromophore-Protein Interplay During the Phytochrome Photocycle Revealed by Step-Scan FTIR Spectroscopy
2018
Phytochrome proteins regulate many photoresponses of plants and microorganisms. Light absorption causes isomerization of the biliverdin chromophore, which triggers a series of structural changes to activate the signaling domains of the protein. However, the structural changes are elusive, and therefore the molecular mechanism of signal transduction remains poorly understood. Here, we apply two-color step-scan infrared spectroscopy to the bacteriophytochrome from Deinococcus radiodurans. We show by recordings in H2O and D2O that the hydrogen bonds to the biliverdin D-ring carbonyl become disordered in the first intermediate (Lumi-R) forming a dynamic microenvironment, then completely detach …
Coordination of the biliverdin D-ring in bacteriophytochromes.
2018
Phytochrome proteins translate light into biochemical signals in plants, fungi and microorganisms. Light cues are absorbed by a bilin chromophore, leading to an isomerization and a rotation of the D-ring. This relays the signal to the protein matrix. A set of amino acids, which is conserved across the phytochrome superfamily, holds the chromophore in the binding pocket. However, the functional role of many of these amino acids is not yet understood. Here, we investigate the hydrogen bonding network which surrounds the D-ring of the chromophore in the resting (Pr) state. We use UV/vis spectroscopy, infrared absorption spectroscopy and X-ray crystallography to compare the photosensory domains…
Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein
2016
Many biological processes depend on detecting and responding to light. The response is often mediated by a structural change in a protein that begins when absorption of a photon causes isomerization of a chromophore bound to the protein. Pande et al. used x-ray pulses emitted by a free electron laser source to conduct time-resolved serial femtosecond crystallography in the time range of 100 fs to 3 ms. This allowed for the real-time tracking of the trans-cis isomerization of the chromophore in photoactive yellow protein and the associated structural changes in the protein.Science, this issue p. 725A variety of organisms have evolved mechanisms to detect and respond to light, in which the re…
Biological activity of PtIV prodrugs triggered by riboflavin-mediated bioorthogonal photocatalysis
2018
AbstractWe have recently demonstrated that riboflavin (Rf) functions as unconventional bioorthogonal photocatalyst for the activation of PtIV prodrugs. In this study, we show how the combination of light and Rf with two PtIV prodrugs is a feasible strategy for light-mediated pancreatic cancer cell death induction. In Capan-1 cells, which have high tolerance against photodynamic therapy, Rf-mediated activation of the cisplatin and carboplatin prodrugs cis,cis,trans-[Pt(NH3)2(Cl)2(O2CCH2CH2CO2H)2] (1) and cis,cis,trans-[Pt(NH3)2(CBDCA)(O2CCH2CH2CO2H)2] (2, where CBDCA = cyclobutane dicarboxylate) resulted in pronounced reduction of the cell viability, including under hypoxia conditions. Such …