Leaf-age dependent response of carotenoid accumulation to elevated CO₂ in Arabidopsis

Carotenoids contribute to photosynthesis, photoprotection, phytohormone and apocarotenoid biosynthesis in plants. Carotenoid-derived metabolites control plant growth, development and signalling processes and their accumulation can depend upon changes in the environment. Elevated carbon dioxide (eCO₂) often enhances carbon assimilation, early growth patterns and overall plant biomass, and may increase carotenoid accumulation due to higher levels of precursors from isoprenoid biosynthesis. Variable effects of eCO₂ on carotenoid accumulation in leaves have been observed for different plant species. Here, we determined whether the variable response of carotenoids to eCO₂ was potentially a function of leaf age and the impact of eCO₂ on leaf development by growing Arabidopsis in ambient CO₂ (400 ppm) and eCO₂ (800 ppm). eCO₂ increased plant leaf number, rosette area, biomass, seed yield and net photosynthesis. In addition, eCO₂ increased carotenoid content by 10-20% in younger emerging leaves, but not in older mature leaves. Older leaves contained approximately 60% less total carotenoids compared to younger leaves. The age-dependent effect on carotenoid content was observed for cotyledon, juvenile and adult phase leaves. We conclude that younger leaves utilize additional carbon from enhanced photosynthesis in eCO₂ to increase carotenoid content, yet older leaves have less capacity to store additional carbon into carotenoids.