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Special Issue "Photosystem II Photochemistry in Biotic and Abiotic Stress"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Photochemistry".

Deadline for manuscript submissions: 30 September 2021.

Special Issue Editor

Prof. Dr. Michael Moustakas
E-Mail Website
Guest Editor

Special Issue Information

Dear Colleagues,

Photosynthesis is the process by which organisms convert absorbed solar energy into chemical energy via photosystem II (PSII) and photosystem I (PSI). In the light reactions of photosynthesis, the absorbed light as photons by the light-harvesting complexes (LHCs) is transferred to the reaction centers (RCs), where through charge separation, the electrons flow from photosystem II (PSII) through cytochrome b6f and diffusible electron carriers to photosystem I (PSI). PSII and PSI, which work coordinately for efficient electron transfer, are located in the photosynthetic membranes of chloroplasts, the thylakoids. Chloroplasts exhibit stacked and unstacked thylakoid membranes, designated as grana and stroma thylakoids, respectively. The two photosystems, PSI and PSII, are laterally and functionally separated mainly into the stroma (non-appressed) and grana (appressed) thylakoid membranes, respectively, that allow the regulation of the excitation energy distribution between the two photosystems. PSII is a multi-protein super-complex that initiates electron transport within the thylakoid membrane, catalyzing one of the most exciting reactions in nature, the light-driven oxidation of H2O and the production of O2. PSII eventually provides the electrons required for the conversion of inorganic molecules into the organic molecules and establishes itself as the engine of life. In the light reactions, the result is the generation of a proton gradient (ΔpH) for ATP synthesis and the reduction of NADP+ by the electrons transferred.

In light reactions of photosynthesis, reactive oxygen species (ROS), such as superoxide anion radical (O2), hydrogen peroxide (H2O2), and singlet oxygen (1O2) are continuously produced at basal levels that are incapable of causing damage, as they are being scavenged by different antioxidant mechanisms. Under most biotic or abiotic stresses the absorbed light energy exceeds what can be used and, thus, it can damage the photosynthetic apparatus, with PSII being particularly exposed to damage. If this excess excitation energy is not quenched by the photoprotective mechanism of non-photochemical quenching (NPQ), increased production of ROS occurs that can lead to oxidative stress. Thus, under biotic or abiotic stress, the oxidative stress that results from an imbalance between ROS production and scavenging by the antioxidant mechanisms can cause cellular damage that can lead to cell death. The response of plants to this imbalance before damage to their cellular structures is critical for maintaining high rates of photosynthesis and also for their survival. Nevertheless, these ROS signals not only provide cells with tools to monitor electron transport and, thus, prevent over-reduction or over-oxidation, but also produce redox regulatory networks that facilitate plants to sense and respond to biotic and abiotic stress conditions.

We encourage original research submissions, as well as review/mini-review articles, concerning basic aspects and future research directions in the field.

Prof. Dr. Michael Moustakas
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Photosynthesis
  • Light reactions
  • Electron transport
  • Chlorophyll fluorescence
  • Excitation energy
  • Light-harvesting complex
  • Antioxidant mechanisms
  • Thylakoids
  • Reaction centers
  • Stacked and un-stacked membranes
  • Reactive oxygen species (ROS)
  • ROS production and scavenging
  • Superoxide anion radical
  • Hydrogen peroxide
  • Proton gradient (ΔpH)
  • Singlet oxygen
  • Oxidative stress
  • Environmental stress
  • Redox regulation

Published Papers (2 papers)

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Research

Open AccessArticle
Changes in Light Energy Utilization in Photosystem II and Reactive Oxygen Species Generation in Potato Leaves by the Pinworm Tuta absoluta
by , , , , and
Molecules 2021, 26(10), 2984; https://doi.org/10.3390/molecules26102984 - 18 May 2021
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Abstract
We evaluated photosystem II (PSII) functionality in potato plants (Solanum tuberosum L.) before and after a 15 min feeding by the leaf miner Tuta absoluta using chlorophyll a fluorescence imaging analysis combined with reactive oxygen species (ROS) detection. Fifteen minutes after feeding, [...] Read more.
We evaluated photosystem II (PSII) functionality in potato plants (Solanum tuberosum L.) before and after a 15 min feeding by the leaf miner Tuta absoluta using chlorophyll a fluorescence imaging analysis combined with reactive oxygen species (ROS) detection. Fifteen minutes after feeding, we observed at the feeding zone and at the whole leaf a decrease in the effective quantum yield of photosystem II (PSII) photochemistry (ΦPSII). While at the feeding zone the quantum yield of regulated non-photochemical energy loss in PSII (ΦNPQ) did not change, at the whole leaf level there was a significant increase. As a result, at the feeding zone a significant increase in the quantum yield of non-regulated energy loss in PSII (ΦNO) occurred, but there was no change at the whole leaf level compared to that before feeding, indicating no change in singlet oxygen (1O2) formation. The decreased ΦPSII after feeding was due to a decreased fraction of open reaction centers (qp), since the efficiency of open PSII reaction centers to utilize the light energy (Fv′/Fm′) did not differ before and after feeding. The decreased fraction of open reaction centers resulted in increased excess excitation energy (EXC) at the feeding zone and at the whole leaf level, while hydrogen peroxide (H2O2) production was detected only at the feeding zone. Although the whole leaf PSII efficiency decreased compared to that before feeding, the maximum efficiency of PSII photochemistry (Fv/Fm), and the efficiency of the water-splitting complex on the donor side of PSII (Fv/Fo), did not differ to that before feeding, thus they cannot be considered as sensitive parameters to monitor biotic stress effects. Chlorophyll fluorescence imaging analysis proved to be a good indicator to monitor even short-term impacts of insect herbivory on photosynthetic function, and among the studied parameters, the reduction status of the plastoquinone pool (qp) was the most sensitive and suitable indicator to probe photosynthetic function under biotic stress. Full article
(This article belongs to the Special Issue Photosystem II Photochemistry in Biotic and Abiotic Stress)
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Open AccessArticle
A Computational Study of the S2 State in the Oxygen-Evolving Complex of Photosystem II by Electron Paramagnetic Resonance Spectroscopy
Molecules 2021, 26(9), 2699; https://doi.org/10.3390/molecules26092699 - 04 May 2021
Viewed by 292
Abstract
The S2 state produces two basic electron paramagnetic resonance signal types due to the manganese cluster in oxygen-evolving complex, which are influenced by the solvents, and cryoprotectant added to the photosystem II samples. It is presumed that a single manganese center oxidation [...] Read more.
The S2 state produces two basic electron paramagnetic resonance signal types due to the manganese cluster in oxygen-evolving complex, which are influenced by the solvents, and cryoprotectant added to the photosystem II samples. It is presumed that a single manganese center oxidation occurs on S1 → S2 state transition. The S2 state has readily visible multiline and g4.1 electron paramagnetic resonance signals and hence it has been the most studied of all the Kok cycle intermediates due to the ease of experimental preparation and stability. The S2 state was studied using electron paramagnetic resonance spectroscopy at X-band frequencies. The aim of this study was to determine the spin states of the g4.1 signal. The multiline signal was observed to arise from a ground state spin ½ centre while the g4.1 signal generated at ≈140 K NIR illumination was proposed to arise from a spin 52 center with rhombic distortion. The ‘ground’ state g4.1 signal was generated solely or by conversion from the multiline. The data analysis methods used involved numerical simulations of the experimental spectra on relevant models of the oxygen-evolving complex cluster. A strong focus in this paper was on the ‘ground’ state g4.1 signal, whether it is a rhombic 52 spin state signal or an axial 32 spin state signal. The data supported an X-band CW-EPR-generated g4.1 signal as originating from a near rhombic spin 5/2 of the S2 state of the PSII manganese cluster. Full article
(This article belongs to the Special Issue Photosystem II Photochemistry in Biotic and Abiotic Stress)
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