Probing the kinetics of Photosystem I and Photosystem II fluorescence in pea chloroplasts on a picosecond pulse fluorometer

Picosecond fluorescence kinetics of pea chloroplasts have been investigated at room temperature using a pulse fluorometer with a resolution time of 10^?11 s. Fluorescence has been excited by both a ruby and neodymium-glass mode-locked laser and has been recorded within the 650 to 800 nm spectral region.We have found three-component kinetics of fluorescence from pea chloroplasts with lifetimes of 80, 300 and 4500 ps, respectively. The observed time dependency of the fluorescence of different components on the functional state of the photosynthetic mechanism as well as their spectra enabled us to conclude that Photosystem I fluoresces with a lifetime of 80 ps (τ_I) and Photosystem II fluoresces with a lifetime of 300 ps (τ_II). Fluorescence with a lifetime of 4500 ps (τ_III) may be interpreted as originating from chlorophyll monomeric forms which are not involved in photosynthesis.It was determined that the rise time of Photosystem I and Photosystem II fluorescence after 530 nm photoexcitation is 200 ps, which corresponds to the time of energy migration to them from carotenoids.