Light-induced free radical production in chloroplast fragments having a 740 mμ absorbancy maximum

Abstract

Chloroplast fragments having an absorbancy maximum at 740 mμ contain unpaired electrons, as determined by the electron spin resonance (ESR) technique. On illumination, the number of unpaired electrons is increased 2–8-fold. The light and dark signals occur at g = 2.002 and have a peak to peak width of about 1 gauss. The ESR signal gradually disappears as the methanol concentration is increased to the point where the chlorophylls are extracted. Cupric ion was found to increase the light and dark ESR signals and at concentrations of 10 −2 M to inhibit the production of a light induced signal. Kinetic analysis indicates that two processes participate in the onset and decay of this signal. Analysis of the relative amounts of these two components induced by different wavelengths of light indicate that two pigment systems are involved. These results are compared with those from previous ESR studies of photosynthetic materials.