Chemical quenching of singlet oxygen by plastoquinols and their oxidation products in Arabidopsis

Abstract

Summary Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen ( 1 O 2 ) formed during high light stress in higher plants. Although quenching of 1 O 2 by prenylquinols has been previously studied, direct evidence for chemical quenching of 1 O 2 by plastoquinols and their oxidation products is limited in vivo . In the present study, the role of plastoquinol‐9 ( PQH 2 ‐9) in chemical quenching of 1 O 2 was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene ( SPS 1oex) involved in PQH 2 ‐9 and plastochromanol‐8 biosynthesis. In this work, direct evidence for chemical quenching of 1 O 2 by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques in vivo . Chemical quenching of 1 O 2 was associated with consumption of PQH 2 ‐9 and formation of its various oxidized forms. Oxidation of PQH 2 ‐9 by 1 O 2 leads to plastoquinone‐9 ( PQ ‐9), which is subsequently oxidized to hydroxyplastoquinone‐9 [ PQ ( OH )‐9]. We provide here evidence that oxidation of PQ ( OH )‐9 by 1 O 2 results in the formation of trihydroxyplastoquinone‐9 [ PQ ( OH ) 3 ‐9]. It is concluded here that PQH 2 ‐9 serves as an efficient 1 O 2 chemical quencher in Arabidopsis, and PQ ( OH ) 3 ‐9 can be considered as a natural product of 1 O 2 reaction with PQ ( OH )‐9. The understanding of the mechanisms underlying 1 O 2 chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.