Journal Article

The Excess Light Energy that is neither Utilized in Photosynthesis nor Dissipated by Photoprotective Mechanisms Determines the Rate of Photoinactivation in Photosystem II

Masaharu C. Kato, Kouki Hikosaka, Naoki Hirotsu, Amane Makino and Tadaki Hirose

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 3, pages 318-325
Published in print March 2003 | ISSN: 0032-0781
Published online March 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg045
The Excess Light Energy that is neither Utilized in Photosynthesis nor Dissipated by Photoprotective Mechanisms Determines the Rate of Photoinactivation in Photosystem II

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Photoinactivation of PSII is thought to be caused by the excessive light energy that is neither used for photosynthetic electron transport nor dissipated as heat. However, the relationship between the photoinactivation rate and excess energy has not been quantitatively evaluated. Chenopodium album L. plants grown under high-light and high-nitrogen (HL-HN) conditions show higher tolerance to photoinactivation and have higher photosynthetic capacity than the high-light and low-nitrogen (HL-LN)- and low-light and high-nitrogen (LL-HN)-grown plants. The rate of photoinactivation in the LL-HN plants was faster than that in the HL-LN, which was similar to that in the HL-HN plants, while the LL-HN and HL-LN plants had similar photosynthetic capacities [Kato et al. (2002b) Funct. Plant Biol. 29: 787]. We quantified partitioning of light energy between the electron transport and heat dissipation at the light intensities ranging from 300 to 1,800 µmol m–2 s–1. The maximum electron transport rate was highest in the HL-HN plants, heat dissipation was greatest in the HL-LN plants, and the excess energy, which was neither consumed for electron transport nor dissipated as heat, was greatest in the LL-HN plants. The first-order rate constant of the PSII photoinactivation was proportional to the magnitude of excess energy, with a single proportional constant for all the plants, irrespective of their growth conditions. Thus the excess energy primarily determines the rate of PSII photoinactivation. A large photosynthetic capacity in the HL-HN plants and a large heat dissipation capacity in the HL-LN plants both contribute to the protection of PSII against photoinactivation.

Keywords: Keywords: Acclimation — Chenopodium album — Heat dissipation — Photoinhibition — Photoprotection —Xanthophyll cycle.; Abbreviations: A, antheraxanthin; Ci, intercellular CO2 concentration; D, fraction of light energy that is dissipated in the light; E, fraction of excess energy; Fm, maximal fluorescence level in the dark; Fo minimal fluorescence level in the dark; Fs, actual fluorescence level; Fv, variable fluorescence level in the dark; Fm′, maximal fluorescence in the light; Fo′, minimal fluorescence in the light; Fv′/Fm′, quantum yield of electron transport in open PSII; ΔF/Fm′, quantum yield of PSII electron transport; HL-HN, high-light and high-nitrogen; HL-LN, high-light and low-nitrogen; kpi, rate constant of photoinactivation; L, fraction of light energy that is dissipated in the dark; LL-HN, low-light and high-nitrogen; P, fraction of light energy that is consumed by electron transport; PPFD, photosynthetically active photon flux density; QA, primary quinone acceptor in PSII; qP, photochemical quenching; V, violaxanthin; Z, zeaxanthin.

Journal Article.  5744 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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