Photodynamics of the Bacteriochlorophyll-Carotenoid System. 1. Bacteriochlorophyll-photosensitized Oxygenation of β-Carotene in Acetone¶

Abstract

Carotenoids are well-known physical quenchers of chlorophyll excited states and reactive oxygen species both in vivo and in vitro. They may also be involved in chemical quenching undergoing, e.g. isomerizations or oxidations. We have found that ␤-carotene (Car) in aerobic acetone is rapidly oxygenated under strong illumination with red light ( exc Ն 630 nm) in the presence of bacteriopheophytin a. At the same time the photosensitizer undergoes only slight (Ͻ10%) photodegradation. By preparative high-performance liquid chromatography as many as seven major products of oxygen attachment to Car have been isolated. Their molecular masses show that Car sequentially accumulates up to six oxygen atoms while its C 40 -skeleton remains intact.

Chemical Quenching of Singlet Oxygen by Carotenoids in Plants

“…For b-carotene and lutein, the accumulation of the endoperoxide (m/z 569 and 602, respectively) occurred during the first 15 min of illumination and then declined. A similar transitory accumulation of b-carotene endoperoxide was reported for bacteriochlorophyll-photosensitized oxidation of b-carotene in vitro (Fiedor et al, 2001). In Figure 1.…”

“…High-light stress induced an increase in the b-carotene endoperoxide levels, but this effect was not more pronounced in the cat2 mutant compared with the wild type, confirming that this compound is specific to 1 O 2 attack on b-carotene. This study has identified a rather large range of products generated during the in vitro oxidation of b-carotene and xanthophylls by 1 O 2 , thus extending previous studies (Stratton et al, 1993;Yamauchi et al, 1998;Fiedor et al, 2001;Montenegro et al, 2002). More precisely, the presented results confirm the formation of an endoperoxide that appears to be a major oxidation product for both b-carotene and xanthophylls.…”

“…In this previous study, the major oxidation product was identified as b-carotene endoperoxide. This compound was also reported to be a major product generated in vitro from b-carotene by (bacterio) chlorophyll-sensitized photooxidation (Yamauchi et al, 1998;Fiedor et al, 2001) and was even identified as the primary oxidation products in early stage photolyzed solution of b-carotene (Montenegro et al, 2002). We collected the compound eluted in peak 6 and measured its absorbance spectrum in methanol/hexane (Fig.…”

“…Nevertheless, in vitro experiments have shown that carotenoids in solvent can be oxidized by 1 O 2 , thus indicating the existence of a chemical quenching capacity for those compounds (Foote and Denny, 1968;Stratton et al, 1993;Yamauchi et al, 1998;Fiedor et al, 2001;Montenegro et al, 2002). However, the occurrence of this mechanism in vivo during exposure of plants to high-light stress is not documented.…”

Expression of Enzymes Involved in Chlorophyll Catabolism in Arabidopsis Is Light Controlled

“…Only in the last decade or so, since the characterization of several intermediate catabolites of Chl accompanied by advances in molecular biology methods for identifying the enzymes involved, has the process appeared less enigmatic (Gossauer and Engel, 1996;Hörtensteiner, 1999;Kräutler and Matile, 1999;Matile, 2000;Oberhuber et al, 2003;Kräutler and Hörtensteiner, 2006;Kräutler, 2008). Now it is seen as a sequence of well-synchronized steps in the safe withdrawal of Chl molecules, which, once released from photosynthetic complexes, become photocytotoxic due to the photodynamic effect (Fiedor et al, 1993(Fiedor et al, , 2001. The withdrawal of Chls also seems correlated with other processes of salvaging thylakoid proteins and lipids (Ischebeck et al, 2006).…”