A newly developed fluorescence measuring system is employed for the recording of chlorophyll fluorescence induction kinetics (Kautsky-effect) and for the continuous determination of the photochemical and non-photochemical components of fluorescence quenching. The measuring system, which is based on a pulse modulation principle, selectively monitors the fluorescence yield of a weak measuring beam and is not affected even by extremely high intensities of actinic light. By repetitive application of short light pulses of saturating intensity, the fluorescence yield at complete suppression of photochemical quenching is repetitively recorded, allowing the determination of continuous plots of photochemical quenching and non-photochemical quenching. Such plots are compared with the time courses of variable fluorescence at different intensities of actinic illumination. The differences between the observed kinetics are discussed. It is shown that the modulation fluorometer, in combination with the application of saturating light pulses, provides essential information beyond that obtained with conventional chlorophyll fluorometers.

A newly developed modulation fluorometer is described which employs repetitive 1 μs Xe-flashes for excitation light. Similar to the standard PAM Chlorophyll Fluorometer, which uses 1 μs LED pulses for measuring light, the integrated measuring light intensity is sufficiently low to monitor the dark-fluorescence level, Fo. The maximal fluorescence yield, Fm, can be determined with high selectivity upon application of a saturating light pulse. The Xe-PAM displays exceptionally high sensitivity, enabling quenching analysis at chlorophyll concentrations as low as 1 μg/l, thus allowing to assess photosynthesis of phytoplankton in natural waters like lakes, rivers and oceans. Due to high flexibility in the choice of excitation and emission wavelengths, this system also provides the experimental basis for a thorough study of fluorescence and photosynthesis properties of various algae classes with differing antenna organisation. By appropriate modifications, the instrument may as well be used to measure with great sensitivity and selectivity other types of fluorescence (e.g. NADPH-fluorescence), as well as light-scattering and absorbance changes.

A newly developed compact instrument is described for the measurement of chlorophyll luminescence induction in plants. The instrument operates with a pulsed light emitting diode (LED) as light source and a photodiode as luminescence detector. A special emitter-detector geometry provides for high irradiance of the sample and efficient collection of luminescence by the detector. With insertion of appropriate filters the same probe is also suited for measuring prompt chlorophyll fluorescence. The instrument shows considerable flexibility with respect to pulse frequency, relative lengths of light/dark intervals and luminescence sampling periods. Due to a selective amplifier system only that part of luminescence is processed which is induced by the individual excitation pulses. By this approach, the problem of "slow phase accumulation", encountered with conventional phosphoroscopes, is eliminated. Some examples are given for system operation, demonstrating satisfactory performance in measurements with intact leaves and isolated chloroplasts.