Light-induced heat production correlated with fluorescence and its quenching mechanisms.

Light-induced heat produced by the non-radiative decay represents one way of de-excitation after excitation by light absorption. It was detected in vivo with cotyledons of radish seedlings (Raphanus sativus L.) by measuring the photoacoustic signal at a modulation frequency of 279 Hz. During the induction kinetic of photosynthesis the photoacoustic signal, the chlorophyll fluorescence as well as the photochemical and the non-photochemical quenching of fluorescence were simultaneously determined in order to get information about the correlation of heat production, fluorescence and its quenching mechanisms. Our results demonstrate that the changes of the photoacoustic signal can in most cases be related directly or indirectly to changes in the photochemical activity. However the kinetic of the photoacoustic signal differs from that of the fluorescence and from that of the non-photochemical quenching. This indicates that the sum of energy dissipation processes resulting in the production of light-induced heat and measured by the high-frequency photoacoustic signal must be taken into account when judging photosynthetic activity.