[Further studies on the variability of the photosynthetic unit]

The light saturation curves of photosynthesis of a yellow Chlorella mutant and the normal green strain have been investigated with monochromatic light at 15 different wavelengths in the range from 400 to 700 nm.The concentration of lipophilic quinones in relation to the chlorophyll content at different stages of regreening has also been studied. 1. On the basis of the amount of chlorophyll the photosynthetic efficiency of the yellow-green Chlorella mutant in red light of 672 and 681 nm wavelength is five times as great as that of the normal green type. On the basis of dry weight the two strains fix about the same amount of CO2. 2. In the mutant light saturation always occurs at higher intensities than in the normal strain. 3. Under conditions of light saturation maximal photosynthetic activity of the mutant is less in white light than in red light. 4. The ratio molecules quinone/molecules chlorophyll of the mutant is much higher than that of the normal control. 5. The results 1-4 are explained by the variability of the size of the photosynthetic unit. In the normal form 460 chlorophyll molecules are available for one electron transport system, that is system I and system II together, or 230 molecules per quantum absorbed. In the mutant there are only 80-100 molecules present, or 40-50 molecules per quantum absorbed.For maximum photosynthetic efficiency 30-50 molecules of chlorophyll per unit are needed. 6. Blue light, especially of 452 nm wavelength, strongly inhibits CO2 fixation in the mutant, which then increases slowly in a following red light period.