Characterization of the quenching of chlorophyll a fluorescence by β-carotene using the non-linear analysis

Carotenoids (Car) regulate energy flow in photosynthesis by a specific Car-chlorophyll (Chl) interaction in the singlet-excited states, leading to a reduction in Chl fluorescence. We studied quenching of Chl a-fluorescence in benzene by trans-beta-carotene. Non-linear analysis of the quenching process enables to explain the possible molecular mechanism leading to the de-excitation of Chl a. The fluorescence intensity was measured at 670 nm for excitation wavelengths of 380, 430, 640, and 650 nm. The beta-carotene concentrations ranged from 4 x 10(-5) M to 5 x 10(-3) M. When the samples were excited at 640 and 650 nm, the Stern-Volmer plots showed that the quenching process has high rate constants, hence carotene is a very efficient quencher. Two different types of quenching process could take place.