Progress in Chlorophyll Fluorescence Research: Major Developments During the Past Years in Retrospect

Abstract

During the past years chlorophyll fluorescence has developed as one of the most frequently used measuring tools in plant science. This somewhat unexpected and remarkable development was triggered by recent progress in instrumentation for measuring fluorescence yield under ambient light conditions and by the increased awareness among plant scientists, as in the general public, of aspects of environmental and stress physiology. Since the discovery of the “Kautsky effect” in 1931, fluorescence had always served as a pioneer tool. However, for more than 50 years it was mainly used by biophysically oriented scientists for basic photosynthesis research. The phenomenology of fluorescence changes in intact cells was considered far too complex to provide more than qualitative information. Because the fluorescence characteristics were known to be strongly affected by preillumination, it appeared necessary to thoroughly dark-adapt a sample before recording dark-light induction curves. Additionally, as the complexity of fluorescence changes increased with increasing illumination time, it was mostly the rapid initial induction kinetics which were analyzed to assess the functioning of the primary reactions. Within less than a decade, a completely different situation has evolved. Along with the availability of new instrumentation and analytical methods for fluorescence analysis under normal daylight conditions, the interest has shifted from the primary reactions to the level of overall electron transport efficiency and photosynthesis regulation, and from induction kinetics to investigations of steady-state reactions. Chlorophyll fluorescence, which used to be a tool preferentially applied in dark laboratories, has made the step into the full sunlight, where in situ photosynthesis takes place with all its intricate and still poorly understood regulatory mechanisms in response to environmental factors.