Understanding the regulation of carotenoid metabolism (synthesis, conversion and degradation) in plants requires turnover measurement of individual carotenoids, apocarotenoids and precursors. In our previous study, we demonstrated continuous turnover of carotenes together with chlorophyll a in illuminated leaves of Arabidopsis thaliana by using 14CO2 pulse-chase labeling. In contrast to carotenes and chlorophyll a that are bound in photosystem reaction center complexes, xanthophylls and chlorophyll b, which are bound in light-harvesting antenna complexes, were hardly labeled by 14C within a day, even when the total amount of xanthophyll-cycle pigments (zeaxanthin, antheraxanthin, and violaxanthin) was increasing, presumably by de novo synthesis, under strong light. In order to obtain quantitative information of carotenoid turnover in leaves of intact plants, we constructed a labelling chamber in which 15 small plants, such as Arabidopsis, can be synchronously labelled by 13CO2 over days. First we tested the chamber by operating with 12CO2 while continuously monitoring the conditions inside the chamber (light intensity, air temperature and humidity, CO2 concentration, pressure). Then a protocol was established to grow 15 Arabidopsis plants (wildtype Columbia-0) in the chamber under the light intensity of ~200 µmol photons m-2 s-1. Switching to 13CO2, plants were grown in the chamber under the same conditions for up to seven days. LC-MS analysis of pigments extracted from rosette leaves of the 13C-labelled Arabidopsis plants showed a substantial incorporation of photosynthetically fixed 13C into β-carotene and lutein along with chlorophyll a and chlorophyll b. The proposed system can be used for pulse-chase experiments (from 12CO2 to 13CO2 and vice versa) to estimate the turnover rate of carotenoids and chlorophylls as well as other plant metabolites. Results from such experiments could provide missing pieces of information in the current picture of metabolic pathway regulation in plants
