Lighting the path:a tribute to Robert Emerson (1903-1959)

Abstract

Today, we shall re-live the discoveries of the basic concepts of the light reactions of oxygenic photosynthesis. The concept of the Photosynthetic Unit, and the quantum efficiency emerged as early topics of quantitative studies. Determination of the minimum number of quanta needed for the release of one O2 molecule had a long and bitter controversy. According to Otto Warburg (1883-1970), the minimum quantum requirement per O2 was between 2.8 and 4. The experiments of Robert Emerson (1901-1959), on the other hand, gave values of 8 to 12. The latter range was finally accepted. A number of important basic discoveries led to support the two-light reaction/two photosystem scheme of photosynthesis that we now use as the basis of design of further research. These discoveries will be considered, and include: the Emerson Enhancement Effect, the Hill Reaction, and the existence of different spectral forms of Chl a. Several kinds of experimental evidence reinforced the two-light/two-photosystem concept; the researches of Bessel Kok, Lou Duysens, Jan Amesz and Horst Witt were particularly significant. The theoretical ideas of Hans Gaffron, James Franck and Eugene Rabinowitch, the experiments of William Arnold, Larry Blinks, and C. Stacy French, and the challenges of Daniel Arnon added much spice to the evolution of our current understanding. It was, however, the biochemical insights of Robin Hill (1899-1991) that rationalized the diverse kinds of evidence that accounted for the experimental facts in terms of the two-light/two-photosystem mechanism, popularly known as the "Z¿ scheme.