TWO LIGHT REACTIONS IN TPN REDUCTION BY SPINACH CHLOROPLASTS.

Abstract The long-wavelength photoreaction of photosynthesis may be studied by the addition of reduced indophenol dyes to chloroplasts. The reduction of TPN with this system, which is most efficient at far-red wavelengths, proceeds with a quantum yield of close to one TPN equivalent per quantum absorbed. In contrast, the normal TPN Hill reaction is sensitized by shorter wavelengths and requires two quanta per equivalent of TPN reduced. The light kinetics and wavelength dependence of the quantum yields for these systems are presented.