Light-induced Cell Division in Chlorella vulgaris, Beijerinck (Emerson Strain)

Abstract

The inability of the Emerson strain of Chlorella vulgaris to grow and divide actively in a glucose medium in the dark has been confirmed. It has been shown that although glucose does not enhance the rate of cell-division when added to cultures growing under saturating photosynthetic conditions, it nevertheless markedly increases the growth-rate when supplied to cultures in which photosynthesis is limited by an inadequate CO₂ supply. Transfer of actively growing cultures from light to darkness is followed by a limited period of active cell-division if glucose is added to the medium; this has been interpreted as indicating glucose utilization and the synthesis in light only, of some substance(s) essential for cell-division. Further evidence for this view has been obtained from studies of the effect of a light pretreatment on subsequent growth in the dark. With cultures aerated with CO₂-free air, re-exposure to light after a period in the dark has been shown to bring about a resumption of active cell-division accompanied by a decrease in the percentage of ‘giant’ cells in the population. This also suggests the participation of some photo-reaction, other than photosynthesis, in the control of active cell-division in this strain of C. vulgaris.