Tissue-Specific Apocarotenoid Glycosylation Contributes to Carotenoid Homeostasis in Arabidopsis Leaves.

Attaining defined steady-state carotenoid levels requires balancing of the rates governing their synthesis and metabolism. Phytoene formation mediated by phytoene synthase (PSY) is rate limiting in the biosynthesis of carotenoids, whereas carotenoid catabolism involves a multitude of nonenzymatic and enzymatic processes. We investigated carotenoid and apocarotenoid formation in Arabidopsis (Arabidopsis thaliana) in response to enhanced pathway flux upon PSY overexpression.

Altered turnover of β-carotene and Chl a in Arabidopsis leaves treated with lincomycin or norflurazon.

Interactions between β-carotene (β-C) and Chl a turnover were investigated in relation to photoinhibition and D1 protein turnover in mature leaves of Arabidopsis (Arabidopsis thaliana) by ¹⁴CO₂ pulse-chase labeling. Following a 2 h treatment of leaves with water, lincomycin (Linco; an inhibitor of chloroplast protein synthesis) or norflurazon (NF; an inhibitor of carotenoid biosynthesis at phytoene desaturation) in the dark, ¹⁴CO₂ was applied to the leaves for 30 min under control light (CL; 130 μmol photons m⁻² s⁻¹) conditions, followed by exposure to either CL or high light (HL; 1,100 μmol photons m⁻² s⁻¹) in ambient CO₂ for up to 6 h. Under both light conditions, ¹⁴C incorporation was strongly decreased for Chl a and moderately suppressed for β-C in Linco-treated leaves, showing a marked decline of PSII efficiency (F(v)/F(m)) and β-C content compared with water-treated leaves.

Continuous turnover of carotenes and chlorophyll a in mature leaves of Arabidopsis revealed by 14CO2 pulse-chase labeling.

Carotenoid turnover was investigated in mature leaves of Arabidopsis (Arabidopsis thaliana) by 14CO2 pulse-chase labeling under control-light (CL; 130 micromol photons m(-2) s(-1)) and high-light (HL; 1,000 micromol photons m(-2) s(-1)) conditions. Following a 30-min 14CO2 administration, photosynthetically fixed 14C was quickly incorporated in beta-carotene (beta-C) and chlorophyll a (Chl a) in all samples during a chase of up to 10 h. In contrast, 14C was not detected in Chl b and xanthophylls, even when steady-state amounts of the xanthophyll-cycle pigments and lutein increased markedly, presumably by de novo synthesis, in CL-grown plants under HL.