Carotenoid oxidation products are stress signals that mediate gene responses to singlet oxygen in plants

Abstract

1 O 2 (singlet oxygen) is a reactive O 2 species produced from triplet excited chlorophylls in the chloroplasts, especially when plants are exposed to excess light energy. Similarly to other active O 2 species, 1 O 2 has a dual effect: It is toxic, causing oxidation of biomolecules, and it can act as a signal molecule that leads to cell death or to acclimation. Carotenoids are considered to be the main 1 O 2 quenchers in chloroplasts, and we show here that light stress induces the oxidation of the carotenoid β-carotene in Arabidopsis plants, leading to the accumulation of different volatile derivatives. One such compound, β-cyclocitral, was found to induce changes in the expression of a large set of genes that have been identified as 1 O 2 responsive genes. In contrast, β-cyclocitral had little effect on the expression of H 2 O 2 gene markers. β-Cyclocitral–induced reprogramming of gene expression was associated with an increased tolerance to photooxidative stress. The results indicate that β-cyclocitral is a stress signal produced in high light that is able to induce defense mechanisms and represents a likely messenger involved in the 1 O 2 signaling pathway in plants.