Kautsky effect

Abstract: 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.

Abstract: The variable chlorophyll (Chl) a fluorescence yield is known to be related to the photochemical activity of photosystem I1 (PSII) of oxygen-evolving organisms. The kinetics of the fluorescence rise from the minimum yield, F,, to the maximum yield, F,, is a monitor of the accumulation of net reduced primary bound plastoquinone (QA) with time in all the PSII centers. Using a shutter-less system (Plant Efficiency Analyzer, Hansatech, UK), which allows data accumulation over several orders of magnitude of time (40 11s to 120 s), we have measured on a logarithmic time scale, for the first time, the complete polyphasic fluorescence rise for a variety of oxygenic plants and cyanobacteria at different light intensities. With increasing light intensity, the fluorescence rise is changed from a typical 0-I-P characteristic to curves with two intermediate levels J and I, both of which show saturation at high light intensity but different intensity dependence. Under physiological conditions, Chl a fluorescence transients of all the organisms examined follow the sequence of 0-J-I-P. The characteristics of the kinetics with respect to light intensity and temperature suggest that the 0-J phase is the photochemical phase, leading to the reduction of QA to QA-. The intermediate level I is suggested to be related to a heterogeneity in the filling up of the plastoquinone pool. The P is reached when all the plastoquinone (PQ) molecules are reduced to PQH2. The addition of 3-(3-4-dichIorophenyl)- 1,l -dimethylurea leads to a transformation of the 0-J-I-P rise into an 0-J rise. The kinetics of 0-J-I-P observed here was found to be similar to that of 0-1,-12-P, reported by Neubauer and Schreiber (2. Naturforsch. 42c, 1246-1254, 1987). The biochemical significance of the fluorescence steps 0-J-I-P with respect to the filling up of the plasto- quinone pool by PSII reactions is discussed.

Abstract: Chlorophyll a fluorescence is a highly sensitive, non-destructive, and reliable tool for measuring, rather quickly, photosynthetic efficiency, particularly of Photosystem II (PSII), the water-plastoquinone oxidoreductase. We briefly review here the connection between the fast (up to 2 s) chlorophyll fluorescence rise and PSII, as well as the empirical use of the fluorescence rise kinetics in understanding photosynthetic reactions, particularly of PSII. When dark-adapted photosynthetic samples are exposed to light, a fluorescence induction is observed, known as the Kautsky effect, after Hans Kautsky, the discoverer of the phenomenon showing the existence of variable fluorescence. The chlorophyll fluorescence intensity rises from a minimum level (the O level), in less than 1 s, to a maximum level (the P-level) via two intermediate steps labeled J and I. This is followed by a decline to a lower semi-steady state level, the S level, which is reached in about one minute. We provide here an educational review on how this phenomenon has been exploited through analysis of the fast OJIP fluorescence transient, by discussing basic assumptions, derivation of equations, as well as application to PSII-related questions.

Abstract: In 1931, using their eyes as instruments, H . Kautsky and A . Hirsch related the time course of chlorophyll a fluorescence with photosynthesis in a less-than-one-page article in Naturwissenschaften (see Kautsky's photograph). Chlorophyll a fluorescence is now being used by hundreds of investigators as a probe for various aspects of photosynthesis-from excitation energy transfer in picosecond time scale to CO2 fixation in minutes . It is not only a much used, but also a much abused, tool. It is used because of it being a non-invasive, rapid and a highly sensitive probe, and misused because it is sometimes not recognised that it is affected by various photosynthetic and other reactions. I submit that, like any other technique, if it is used with care and with due regard for its time dependence and competing parameters. it will remain as the one-most powerful tool for probing excitation energy transfer, primary photochemistry, electron flow on both the donor and the acceptor side of photosystem II (PSII) of oxygenic PSII. Further, it is very useful in the quick assay of PSII mutations, and down- regulation and other adjustments to stress (excess light, heat, heavy metal, nutrients and certain herbicides). In this paper, I will present my viewpoint, not a review, on the conceptual and experimental developments in this field. Whenever appropriate, and without any shame and humility, I will include some of my involvement in the excitement surrounding this field. I hope that this paper will serve as a starting point for further discussion of not only the history, but the practical use of chlorophyll a fluorescence as an intrinsic probe of stresses to plants, as well as individual reactions of oxygenic photosynthesis, when combined with other parallel measurements.