Endogenous Singlet Oxygen Photosensitizers in Plants.

Singlet oxygen, a highly reactive oxygen species, is inherently produced in chloroplasts of plants. Chlorophylls are used by plants to harvest light and to transport the singlet electronic excitation from the antenna complexes to the reaction centre (RC) of photosystem I (PSI) and PSII. However, chlorophylls are also efficient photosensitizers of singlet oxygen when they are isolated, when the excitation energy flow is impaired in the antenna complexes, or when the electron transport in PSII is inhibited. In the last case, chlorophyll triplets are formed, and transfer their electronic excitation to molecular oxygen. That chlorophylls act as donors of singlet excitation to other chlorophylls or as donors of triplet excitation to carotenoids as well as molecular oxygen makes singlet oxygen a constant threat for plants. However, plants have developed protection mechanisms for dealing with the danger. Several molecular processes work together in chloroplasts to cope with photosensitization of singlet oxygen and to minimize the resulting damage. Protection utilizes two strategies: to forestall the formation of singlet oxygen (either by preventing the formation of the would-be sensitizer or through deactivating it by a quencher other than molecular oxygen), and to quench, by physical or chemical means, any singlet oxygen that does get formed. Among the photosynthetic complexes, PSII is unique in that its primary electron donor is unprotected by carotenoids and singlet oxygen oxidizes the pigments of PSII RC; intriguingly the carotenoid oxidation products are signalling molecules that can reprogram gene expression. Finally, the distance over which singlet oxygen can diffuse in a viscous cellular medium, as found inside chloroplasts, is analysed.

Bibliographic Details

Main Authors:	Arellano, Juan B., Naqvi, K. Razi
Format:	capítulo de libro biblioteca
Language:	English
Published:	Royal Society of Chemistry (UK) 2016-01
Subjects:	Singlet oxygen, Endogenous photosensitizers, Plants, Photosystem II, Chloroplasts, Chlorophylls, Singlet Oxygen Diffusion, Quenchers,
Online Access:	http://hdl.handle.net/10261/129256
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