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

The inability of the Emerson strain of Chlorella vulgaris togrow and divide actively in a glucose medium in the dark hasbeen confirmed. It has been shown that although glucose doesnot enhance the rate of cell-division when added to culturesgrowing under saturating photosynthetic conditions, it neverthelessmarkedly increases the growth-rate when supplied to culturesin which photosynthesis is limited by an inadequate CO₂ supply. Transfer of actively growing cultures from light to darknessis followed by a limited period of active cell-division if glucoseis added to the medium; this has been interpreted as indicatingglucose utilization and the synthesis in light only, of somesubstance(s) essential for cell-division. Further evidence forthis view has been obtained from studies of the effect of alight pretreatment on subsequent growth in the dark. With cultures aerated with CO₂-free air, re-exposure to lightafter a period in the dark has been shown to bring about a resumptionof active cell-division accompanied by a decrease in the percentageof ‘giant’ cells in the population. This also suggeststhe participation of some photo-reaction, other than photosynthesis,in the control of active cell-division in this strain of C.vulgaris.