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Light intensity

About: Light intensity is a(n) research topic. Over the lifetime, 79515 publication(s) have been published within this topic receiving 1349233 citation(s).
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Journal ArticleDOI
Abstract: Measurements of the quantum yields of chlorophyll fluorescence and CO2 assimilation for a number of plant species exposed to changing light intensity and atmospheric CO2 concentrations and during induction of photosynthesis are used to examine the relationship between fluorescence quenching parameters and the quantum yield of non-cyclic electron transport. Over a wide range of physiological conditions the quantum yield of non-cyclic electron transport was found to be directly proportional to the product of the photochemical fluorescence quenching (qQ) and the efficiency of excitation capture by open Photosystem II (PS II) reaction centres (Fv/Fm). A simple fluorescence parameter, ΔφF/φFm, which is defined by the difference in fluorescence yield at maximal φFm, and steady-state φFs, divided by φFm, can be used routinely to estimate changes in the quantum yield of non-cyclic electron transport. It is demonstrated that both the concentration of open PS II reaction centres and the efficiency of excitation capture by these centres will determine the quantum yield of non-cyclic electron transport in vivo and that deactivation of excitation within PS II complexes by non-photochemical processes must influence the quantum yield of non-cyclic electron transport.

7,262 citations


Journal ArticleDOI
Robert L. Heath1, Lester Packer1Institutions (1)
TL;DR: It is concluded that isolated chloroplasts upon illumination can undergo a cyclic peroxidation initiated by the light absorbed by chlorophyll.
Abstract: A photo-induced cyclic peroxidation in isolated chloroplasts is described In an osmotic buffered medium, chloroplasts upon illumination produce malondialdehyde (MDA)—a decomposition product of tri-unsaturated fatty acid hydroperoxides—bleach endogenous chlorophyll, and consume oxygen These processes show ( a ) no reaction in the absence of illumination; ( b ) an initial lag phase upon illumination of 10–20 minutes duration; ( c ) a linear phase in which the rate is proportional to the square root of the light intensity; ( d ) cessation of reaction occurring within 3 minutes after illumination ceases; and ( e ) a termination phase after several hours of illumination The kinetics of the above processes fit a cyclic peroxidation equation with velocity coefficients near those for chemical peroxidation The stoichiometry of MDA/O 2 = 002, and O 2 Chl bleached = 69 correlates well with MDA production efficiency in other biological systems and with the molar ratio of unsaturated fatty acids to chlorophyll The energies of activation for the lag and linear phases are 17 and 0 kcal/mole, respectively, the same as that for autoxidation During the linear phase of oxygen uptake the dependence upon temperature and O 2 concentration indicates that during the reaction, oxygen tension at the site of peroxidation is 100-fold lower than in the aqueous phase It is concluded that isolated chloroplasts upon illumination can undergo a cyclic peroxidation initiated by the light absorbed by chlorophyll Photoperoxidation results in a destruction of the chlorophyll and tri-unsaturated fatty acids of the chloroplast membranes

7,148 citations


Journal ArticleDOI
Abstract: A systematic study of metal ion doping in quantum (Q)-sized (2-4 nm) TiO_2 colloids is performed by measuring their photoreactivities and the transient charge carrier recombination dynamics. The presence of metal ion dopants in the TiO_2 crystalline matrix significantly influences photoreactivity, charge carrier recombination rates, and interfacial electron-transfer rates. The photoreactivities of 21 metal ion-doped colloids are quantified in terms of both the conduction band electron reduction of an electron acceptor (CCl_4 dechlorination) and the valence band hole oxidation of an electron donor (CHCl_3 degradation). Doping with Fe^(3+), Mo^(5+), Ru^(3+), Os^(3+), Re^(5+), V^(4+), and Rh^(3+) at 0.1-0.5 at.% significantly increases the photoreactivity for both oxidation and reduction while Co^(3+) and Al^(3+) doping decreases the photoreactivity. The transient absorption signals upon laser flash photolysis (λ_(ex) = 355 nm) at λ = 600 nm are extended up to 50 ms for Fe^(3+)-, V^(4+)-, Mo^(5+)-, and Ru^(3+)-doped TiO_2 while the undoped Q-sized TiO_2 shows a complete "blue electron" signal decay within 200 μs. Co^(3+)- and Al^(3+)-doped TiO_2 are characterized by rapid signal decays with a complete loss of absorption signals within 5 μs. The quantum yields obtained during CW photolyses are quantitatively correlated with the measured transient absorption signals of the charge carriers. Photoreactivities are shown to increase with the relative concentration of trapped charge carriers. The photoreactivity of doped TiO_2 appears to be a complex function of the dopant concentration, the energy level of dopants within the TiO_2 lattice, their d electronic configuration, the distribution of dopants, the electron donor concentration, and the light intensity.

3,364 citations



Journal ArticleDOI
Gad Miller1, Nobuhiro Suzuki1, Sultan Ciftci-Yilmaz1, Ron Mittler1  +1 moreInstitutions (2)
TL;DR: An overview of ROS homeostasis and signalling in response to drought and salt stresses is provided and the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses is discussed.
Abstract: Water deficit and salinity, especially under high light intensity or in combination with other stresses, disrupt photosynthesis and increase photorespiration, altering the normal homeostasis of cells and cause an increased production of reactive oxygen species (ROS). ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules. In this review, we provide an overview of ROS homeostasis and signalling in response to drought and salt stresses and discuss the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses.

2,330 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202261
20212,218
20203,306
20193,846
20184,302
20174,068

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Topic's top 5 most impactful authors

Yukio Taniguchi

35 papers, 261 citations

Masakiyo Matsumura

27 papers, 351 citations

René H. Wijffels

24 papers, 1.7K citations

Suresh C. Ameta

23 papers, 207 citations

Eva-Mari Aro

21 papers, 1.8K citations