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33. Enhanced photochemical efficiency of PSII in Prosopis juliflora suggests contribution to invasion advantage over native C3 xero-halophytes under salt stress.

Author

Zia, Ahmad, Gulzar, Salman, and Ruban, Alexander V.

Subjects
PROSOPIS juliflora, HALOPHYTES, CHLOROPHYLL spectra, FLUORIMETRY, FLUORESCENCE quenching, ELECTRON transport
Abstract

Chlorophyll a fluorescence parameters related to PSII photochemistry, photoprotection and photoinhibition were investigated in four C3 plant species growing in their natural habitat: Prosopis juliflora; Abutilon indicum; Salvadora persica; and Phragmites karka. This study compared the light reaction responses of P. juliflora, an invasive species, with three native co-existing species, which adapt to varying water deficit and high salt stress. Chlorophyll a fluorescence quenching analyses revealed that P. juliflora had the highest photochemical quantum efficiency and yield, regulated by higher fraction of open reaction centres and reduced photoprotective energy dissipation without compromising the integrity of photosynthetic apparatus due to photoinhibition. Moreover, the elevated values of parameters obtained through polyphasic chlorophyll a fluorescence induction kinetics, which characterise the photochemistry of PSII and electron transport, highlighted the superior performance index of energy conservation in the transition from excitation to the reduction of intersystem electron carriers for P. juliflora compared to other species. Enhanced pigment contents and their stoichiometry in P. juliflora apparently contributed to upregulating fluxes and yields of energy absorbance, trapping and transport. This enhanced photochemistry, along with reduced non-photochemical processes, could explain the proclivity for invasion advantage in P. juliflora across diverse stress conditions. [ABSTRACT FROM AUTHOR]

Published
2024
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37. Chlorophyll a de-excitation pathways in the LHCII antenna.

Author

Ruban, Alexander V. and Saccon, Francesco

Subjects
*CHLOROPHYLL, *FLUORESCENCE resonance energy transfer, *PHOTOSYSTEMS, *ENERGY storage, *ENERGY transfer, *CHARGE transfer, *CAROTENOIDS
Abstract

Photosystem II (PSII) uses light energy to split water into protons, electrons, and oxygen, ultimately sustaining heterotrophic life on Earth. The major light harvesting complex in plants (LHCII) is packed with chlorophylls and carotenoids and is the main supplier of excitation energy to PSII reaction centers. The protein scaffold acts as a programmed solvent for the pigments in LHCII, tuning their orientations while at the same time impeding concentration quenching to ensure efficient storage of excitation energy by chlorophylls. However, under stress, the very fuel of PSII, solar photons, can damage its delicate inner components and hamper photosynthesis. In a crucial regulatory strategy in plants, LHCII evolved a flexible design that allows it to switch between light-harvesting and dissipative conformations, thereby safely releasing the excess energy that is absorbed into heat. Several mechanisms have been proposed to explain chlorophyll de-excitation pathways in LHCII, such as chlorophyll–chlorophyll charge transfer states, resonance energy transfer from chlorophylls to a carotenoid S1 state, and chlorophyll–carotenoid reductive energy transfer. This Perspective critically assesses the listed proposals, addressing both the physical mechanism of quenching and the nature of the quenching pigment. These hypotheses are then discussed in the context of state-of-the-art biochemical, physiological, and genetic knowledge to scrutinize their likeliness to occur in the native thylakoid membranes. [ABSTRACT FROM AUTHOR]

Published
2022
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45. Photosynthesis in Action : Harvesting Light, Generating Electrons, Fixing Carbon

Author

Ruban, Alexander, Foyer, Christine, Murchie, Erik, Ruban, Alexander, Ruban, Alexander, Foyer, Christine, Murchie, Erik, and Ruban, Alexander

Abstract

Photosynthesis in Action examines the molecular mechanisms, adaptations and improvements of photosynthesis. With a strong focus on the latest research and advances, the book also analyzes the impact the process has on the biosphere and the effect of global climate change. Fundamental topics such as harvesting light, the transport of electronics and fixing carbon are discussed. The book also reviews the latest research on how abiotic stresses affect these key processes as well as how to improve each of them. This title explains how the process is flexible in adaptations and how it can be engineered to be made more effective. End users will be able to see the significance and potential of the processes of photosynthesis. Edited by renowned experts with leading contributors, this is an essential read for students and researchers interested in photosynthesis, plant science, plant physiology and climate change. Provides essential information on the complex sequence of photosynthetic energy transduction and carbon fixation Covers fundamental concepts and the latest advances in research, as well as real-world case studies Offers the mechanisms of the main steps of photosynthesis together with how to make improvements in these steps Edited by renowned experts in the field Presents a user-friendly layout, with templated elements throughout to highlight key learnings in each chapter

Published
2022

47. Ferredoxin C2 is required for chlorophyll biosynthesis and accumulation of photosynthetic antennae in Arabidopsis

Author

Tournaire, Marcela Davalos, Scharff, Lars B., Kramer, Manuela, Goss, Tatjana, Vuorijoki, Linda, Rodriguez-Heredia, Melvin, Wilson, Sam, Kruse, Inga, Ruban, Alexander, Balk L., Janneke, Hase, Toshiharu, Jensen, Poul Erik, Hanke, Guy T., Tournaire, Marcela Davalos, Scharff, Lars B., Kramer, Manuela, Goss, Tatjana, Vuorijoki, Linda, Rodriguez-Heredia, Melvin, Wilson, Sam, Kruse, Inga, Ruban, Alexander, Balk L., Janneke, Hase, Toshiharu, Jensen, Poul Erik, and Hanke, Guy T.

Abstract

Ferredoxins (Fd) are small iron-sulphur proteins, with sub-types that have evolved for specific redox functions. Ferredoxin C2 (FdC2) proteins are essential Fd homologues conserved in all photosynthetic organisms and a number of different FdC2 functions have been proposed in angiosperms. Here we use RNAi silencing in Arabidopsis thaliana to generate a viable fdC2 mutant line with near-depleted FdC2 protein levels. Mutant leaves have ~50% less chlorophyll a and b, and chloroplasts have poorly developed thylakoid membrane structure. Transcriptomics indicates upregulation of genes involved in stress responses. Although fdC2 antisense plants show increased damage at photosystem II (PSII) when exposed to high light, PSII recovers at the same rate as wild type in the dark. This contradicts literature proposing that FdC2 regulates translation of the D1 subunit of PSII, by binding to psbA transcript. Measurement of chlorophyll biosynthesis intermediates revealed a build-up of Mg-protoporphyrin IX, the substrate of the aerobic cyclase. We localise FdC2 to the inner chloroplast envelope and show that the FdC2 RNAi line has a disproportionately lower protein abundance of antennae proteins, which are nuclear-encoded and must be refolded at the envelope after import.

Published
2023

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