Differences in photosynthetic activity between coral sections infested and not infested by boring spionid polychaetes

2006 ◽  
Vol 86 (4) ◽  
pp. 727-728 ◽  
Author(s):  
Jeffrey Wielgus ◽  
Oren Levy
Keyword(s):  
Photosystem Ii ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Repetition Rate ◽  
Photosynthetic Activity ◽  
Mean Value ◽  
Absorption Cross ◽  
Physiological Mechanisms ◽  
Coral Colony ◽  
The Mean

A SCUBA-based fast repetition rate fluorometer (FRRF) was used to study differences in the functional absorption cross-section of Photosystem II (σPSII) between areas of a coral colony of Astreoporamyriophthalma that were infested with spionid polychaetes vs areas lacking worms. The mean value of σPSII in infested areas (mean±SD=347.62±30.67 Å2) was significantly higher than in the areas that were not infested (316.32±17.49 Å2; P<0.0001). Several physiological mechanisms are discussed that may contribute to the observed differences.

State of the phycobilisome determines effective absorption cross-section of Photosystem II in Synechocystis sp. PCC 6803

2021 ◽  
Vol 1862 (12) ◽  
pp. 148494
Author(s):  
Elena A. Protasova ◽  
Taras K. Antal ◽  
Dmitry V. Zlenko ◽  
Irina V. Elanskaya ◽  
Evgeny P. Lukashev ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Absorption Cross ◽  
Effective Absorption ◽  
Synechocystis Sp ◽  
Pcc 6803

scholarly journals Probing functional and optical cross-sections of PSII in leaves during state transitions using fast repetition rate light induced fluorescence transients

2019 ◽  
Vol 46 (6) ◽  
pp. 567 ◽  
Author(s):  
Barry Osmond ◽  
Wah Soon Chow ◽  
Barry J. Pogson ◽  
Sharon A. Robinson
Keyword(s):  
Cross Section ◽  
Absorption Cross Section ◽  
Repetition Rate ◽  
Redox State ◽  
Protein Complexes ◽  
Photochemical Efficiency ◽  
Spectral Composition ◽  
State Transitions ◽  
Absorption Cross ◽  
Wild Type

Plants adjust the relative sizes of PSII and PSI antennae in response to the spectral composition of weak light favouring either photosystem by processes known as state transitions (ST), attributed to a discrete antenna migration involving phosphorylation of light-harvesting chlorophyll-protein complexes in PSII. Here for the first time we monitored the extent and dynamics of ST in leaves from estimates of optical absorption cross-section (relative PSII antenna size; aPSII). These estimates were obtained from in situ measurements of functional absorption cross-section (σPSII) and maximum photochemical efficiency of PSII (φPSII); i.e. aPSII = σPSII/φPSII (Kolber et al. 1998) and other parameters from a light induced fluorescence transient (LIFT) device (Osmond et al. 2017). The fast repetition rate (FRR) QA flash protocol of this instrument monitors chlorophyll fluorescence yields with reduced QA irrespective of the redox state of plastoquinone (PQ), as well as during strong ~1 s white light pulses that fully reduce the PQ pool. Fitting this transient with the FRR model monitors kinetics of PSII → PQ, PQ → PSI, and the redox state of the PQ pool in the ‘PQ pool control loop’ that underpins ST, with a time resolution of a few seconds. All LIFT/FRR criteria confirmed the absence of ST in antenna mutant chlorina-f2 of barley and asLhcb2–12 of Arabidopsis, as well as STN7 kinase mutants stn7 and stn7/8. In contrast, wild-type barley and Arabidopsis genotypes Col, npq1, npq4, OEpsbs, pgr5 bkg and pgr5, showed normal ST. However, the extent of ST (and by implication the size of the phosphorylated LHCII pool participating in ST) deduced from changes in aʹPSII and other parameters with reduced QA range up to 35%. Estimates from strong WL pulses in the same assay were only ~10%. The larger estimates of ST from the QA flash are discussed in the context of contemporary dynamic structural models of ST involving formation and participation of PSII and PSI megacomplexes in an ‘energetically connected lake’ of phosphorylated LHCII trimers (Grieco et al. 2015). Despite the absence of ST, asLhcb2-12 displays normal wild-type modulation of electron transport rate (ETR) and the PQ pool during ST assays, reflecting compensatory changes in antenna LHCIIs in this genotype. Impaired LHCII phosphorylation in stn7 and stn7/8 accelerates ETR from PSII →PQ, over-reducing the PQ pool and abolishing the yield difference between the QA flash and WL pulse, with implications for photochemical and thermal phases of the O-J-I-P transient.

Functionalized gold-nanoparticles enhance Photosystem II driven photocurrent in a hybrid nano-bio-photoelectrochemical cell

2021 ◽  
Author(s):  
Hagit Shoyhet ◽  
Nicholas G. Pavlopoulos ◽  
Lilac Amirav ◽  
Noam Adir
Keyword(s):  
Gold Nanoparticles ◽  
Photosystem Ii ◽  
Solar Energy ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Electrical Current ◽  
Photoelectrochemical Cell ◽  
Photoelectrochemical Cells ◽  
Absorption Cross ◽  
Functionalized Gold Nanoparticles

The use of Photosystem II (PSII) in hybrid bio-photoelectrochemical cells for conversion of solar energy to electrical current is hampered by PSII's narrow absorption cross-section and the generally poor electrical...

scholarly journals Photosynthetic light harvesting and thylakoid organization in a CRISPR/Cas9 Arabidopsis thaliana LHCB1 knockout mutant.

2021 ◽  
Author(s):  
Hamed Sattari Vayghan ◽  
Wojciech J Nawrocki ◽  
Christo Schiphorst ◽  
Dimitri Tolleter ◽  
Hu Chen ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Cross Section ◽  
Photosystem I ◽  
Absorption Cross Section ◽  
Light Harvesting ◽  
Higher Plants ◽  
Oxygenic Photosynthesis ◽  
Growth Delay ◽  
Absorption Cross ◽  
Light Harvesting Complexes

Light absorbed by chlorophylls of photosystem II and I drives oxygenic photosynthesis. Light-harvesting complexes increase the absorption cross-section of these photosystems. Furthermore, these complexes play a central role in photoprotection by dissipating the excess of absorbed light energy in an inducible and regulated fashion. In higher plants, the main light-harvesting complex is the trimeric LHCII. In this work, we used CRISPR/Cas9 to knockout the five genes encoding LHCB1, which is the major component of the trimeric LHCII. In absence of LHCB1 the accumulation of the other LHCII isoforms was only slightly increased, thereby resulting in chlorophyll loss leading to a pale green phenotype and growth delay. Photosystem II absorption cross-section was smaller while photosystem I absorption cross-section was unaffected. This altered the chlorophyll repartition between the two photosystems, favoring photosystem I excitation. The equilibrium of the photosynthetic electron transport was partially maintained by a lower photosystem I over photosystem II reaction center ratio and by the dephosphorylation of LHCII and photosystem II. Loss of LHCB1 altered the thylakoid structure, with less membrane layers per grana stack and reduced grana width. Stable LHCB1 knock out lines allow characterizing the role of this protein in light harvesting and acclimation and pave the way for future in vivo mutational analyses of LHCII.

Nuclear Absorption of Low-Energy Pions

1971 ◽  
Vol 49 (9) ◽  
pp. 1211-1214 ◽  
Author(s):  
Douglas S. Beder
Keyword(s):  
Numerical Calculation ◽  
Nuclear Matter ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Absorption Rate ◽  
Mean Free Path ◽  
Low Energy ◽  
Absorption Cross ◽  
Nuclear Absorption ◽  
The Mean

We derive an expression for the mean free path of low energy π's traversing nuclear matter, assuming that absorption is dominantly on nucleon pairs. Relating the absorption cross section to the data for the inverse reaction NN → NNπ makes this susceptible to numerical calculation. We also discuss how properly to account for nucleon Fermi motion in calculating the absorption rate.

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