Chemical Quenching of Singlet Oxygen by Carotenoids in Plants    

Abstract

Carotenoids are considered to be the first line of defense of plants against singlet oxygen ( 1 O 2 ) toxicity because of their capacity to quench 1 O 2 as well as triplet chlorophylls through a physical mechanism involving transfer of excitation energy followed by thermal deactivation. Here, we show that leaf carotenoids are also able to quench 1 O 2 by a chemical mechanism involving their oxidation. In vitro oxidation of b-carotene, lutein, and zeaxanthin by 1 O 2 generated various aldehydes and endoperoxides. A search for those molecules in Arabidopsis (Arabidopsis thaliana) leaves revealed the presence of 1 O 2 -specific endoperoxides in low-light-grown plants, indicating chronic oxidation of carotenoids by 1 O 2 . b-Carotene endoperoxide, but not xanthophyll endoperoxide, rapidly accumulated during high-light stress, and this accumulation was correlated with the extent of photosystem (PS) II photoinhibition and the expression of various 1 O 2 marker genes. The selective accumulation of b-carotene endoperoxide points at the PSII reaction centers, rather than the PSII chlorophyll antennae, as a major site of 1 O 2 accumulation in plants under high-light stress. b-Carotene endoperoxide was found to have a relatively fast turnover, decaying in the dark with a half time of about 6 h. This carotenoid metabolite provides an early index of 1 O 2 production in leaves, the occurrence of which precedes the accumulation of fatty acid oxidation products.

From ecophysiology to phenomics: some implications of photoprotection and shade–sun acclimation in situ for dynamics of thylakoids in vitro

“…Notably, a recent HPLC -MS study has detected carotenoid endoperoxides, the major oxidative cleavage products of b-C and xanthophylls (Z and L, indistinguishable owing to similar mass) by 1 O 2 , in leaves of Arabidopsis plants grown under low light [41]. However, compared with b-C that undergoes continuous turnover in the light together with Chl a [42], accumulation of L and/or Z endoperoxides in leaves appears to be much less and their levels change little during exposure of plants to high light and low temperature, while the concentrations of b-C endoperoxides more than double under the same condition.…”

Singlet Oxygen Signatures Are Detected Independent of Light or Chloroplasts in Response to Multiple Stresses

“…The chlorophyll triplet state can react with ground state oxygen to make the highly chemically reactive singlet state ( 3 Chl* + 3 O 2 → Chl + 1 O 2 ). Activated chlorophyll can give rise to the triplet state when light energy is inefficiently used, although even normal light conditions may result in detectable formation of singlet oxygen (Triantaphylidès et al, 2008;Ramel et al, 2012a). Singlet oxygen can participate in lipid peroxidation resulting in diagnostic chemical signatures.…”

“…Other scavengers such as ubiquinol, ascorbate, and glutathione may also quench singlet oxygen. Quenching can be physical, involving energy transfer dissipation as heat without scavenger consumption, or can be accompanied by chemical oxidation (Triantaphylidès and Havaux, 2009;Ramel et al, 2012a).…”

Low-molecular-weight metabolite systems chemistry

“…Figure 3 exemplifies structures. For example, carotenoids (3.1) represent terpenoid pigments that protect chloroplasts from the reactive oxygen species singlet oxygen that can be formed by energy transfer from relaxing chlorophyll pigments (Ramel et al, 2012). All animals that are endowed with the ability of sight absorb, transport and metabolize carotenoids into retinoids (3.2) (von Lintig, 2012).…”