Leaf-age dependent response of carotenoid accumulation to elevated CO 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 (eCO) 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 eCO on carotenoid accumulation in leaves have been observed for different plant species. Here, we determined whether the variable response of carotenoids to eCO was potentially a function of leaf age and the impact of eCO on leaf development by growing Arabidopsis in ambient CO (400 ppm) and eCO (800 ppm). eCO increased plant leaf number, rosette area, biomass, seed yield and net photosynthesis. In addition, eCO 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 eCO to increase carotenoid content, yet older leaves have less capacity to store additional carbon into carotenoids.