Enhancement in Chlorella

Abstract

Tne enhancement phenomenon in photosynthesis of Chlorella was studied by means of the Haxo electrode and 2 monochromatic light beams. The short-wave (SW) and long-wave (LW) components of enhancement were examined with the rationale that the characteristics of each are seen most clearly in the presence of an excess of the other. Maximum effect of the LW component is seen only when rate of photosynthesis at short wavelength is about 15 times greater. The spectrum of enhancement for the LW component extends from about 685 m[mu] to at least 650 mu with a peak at 710 m[mu]. Within this region no 2 wavelengths show enhancement but any 1 wave -length shows enhancement with any wavelength in the SW region. Measureable photosynthesis but no evidence of inhibition was observed at 740 - 750 m[mu]. Spectrum of the SW component extends from 685 to less than 420 m[mu]; no 2 wavelengths within this region show enhancement. The 2 enhancement spectra are interpreted as measuring excess absorption by either of 2 pigment systems as a function of wavelength. Comparison of enhancement with relative quantum yield leads to conclusion that at least a major part of enhancement may be attributed to gain in quantum yield for the LW component. Enhancement requires some hypothesis as to mechanism of delivery of quanta from 2 pigment systems to the 2 light reactions of photosynthesis. Present data are best accomodated by what is called a spillover hypothesis: that the LW pigment system delivers quanta only to corresponding light reaction I; that the SW pigment system delivers quanta to light reaction II; that when light reaction II is running in excess, quanta from the SW system are then transferred to light reaction I.