Effects of preillumination with light of different wavelengths on subsequent dark CO₂-fixation in <i>Chlorella</i> cells

Abstract

The effects of preillumination with monochromatic red or blue light on the subsequent dark 14 CO 2 -fixation in Chlorella cells were studied under aerobic as well as anaerobic conditions. When the cell suspension was made aerobic by bubbling air (CO 2 -free) throughout the periods of preillumination and the following dark 14 CO 2 -fixation, the initial fixation product was mainly PGA. The radioactive carbon first incorporated in PGA was transferred mostly to aspartate during the later periods of dark 14 CO 2 -fixation. The rate of 14 C-incorporation into aspartate after preillumination with blue light was 2 to 3 times as high as that observed after red-light pretreatment. The observations support our previous inference that the activity of PEP carboxylase in Chlorella cells is stimulated by preillumination with blue light. When nitrogen gas was used during preillumination and the subsequent dark fixation, the radioactivity of 14 C incorporated during the initial enhanced 14 CO 2 -fixation was eventually transferred to alanine and lactate. The increase in radioactivity of alanine and lactate was more pronounced during dark fixation after preillumination with red light than after preillumination with blue light.