Responses of Heterotrophic Cultures of Chlorella vulgaris Beyerinck to Darkness and Light. I. Pigment and pH Changes.

Glucose cultures of Chlorella vulgaris were grown in white light, in monochromatic light, and in darkness. Difference spectra showed that all wavelengths resulted in increased pigmentation over the dark controls.Cells irradiated with the 600 mmu beam showed a much higher absorption in the blue end of the spectrum with respect to the red end than is normally found in absorption spectra of white-light grown Chlorella cells.Dry weight comparisons between monochromatic light and dark controls showed the controls to be somewhat higher. This demonstrated that the monochromatic irradiation produced pigment synthesis but no increase in growth. Dark growth experiments suggested that cultures incubated in darkness on glucose excreted an acidic product.