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. Partial inhibition of carotenoid biosynthesis by NF caused no or only a minor decrease in F(v)/F(m) and Chl a turnover under both conditions, while the β-C content significantly declined and high ¹⁴C labeling was found for phytoene, the substrate of phytoene desaturase. Together, the results suggest coordinated turnover of Chl a and D1, but somewhat different regulation for β-C turnover, in Arabidopsis leaves. Inhibition of carotenoid biosynthesis by NF may initially enhance metabolic flux in the pathway upstream of phytoene, presumably compensating for short supply of β-C. Our observations are also in line with the notion that HL-induced accumulation of xanthophylls may involve a precursor pool which is distinct from that for β-C turnover.