Adaptation to Quantum Flux by the Emerson Photosynthetic Unit

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Abstract
The size of the Emerson photosynthetic unit was measured in Chlorella pyrenoidosa strain no. 252 grown at light intensities between 50 and 1000 foot candles. The Emerson photosynthetic unit changed from a minimum size of 1970 molecules chlorophyll a + b/O(2) per flash in cells grown at 1000 foot candles to a maximum size of 3150 molecules chlorophyll a + b/O(2) per flash for cells grown at 50 foot candles. The size changes were interpreted as a partial adaptation where the trapping center antenna responded to changes in incident light intensity. Light-induced changes in chlorophyll content and size of the Emerson photosynthetic unit were directly related.Two strains of Chlorella pyrenoidosa adapted by growth to 500 foot candles were then illuminated at the reduced light intensity of 50 foot candles. Emerson photosynthetic unit size (Emerson strain) increased from 2110 molecules Chlorophyll a + b/O(2) per flash at time zero to a maximum size of 3160 after 65 hours at 50 foot candles. The Emerson photosynthetic unit size for strain 252 transferred from 500 to 50 foot candles was 2260 at zero hours and 3650 after 50 hours at 50 foot candles. Emerson photosynthetic unit sizes for similar cultures which remained at 500 foot candles were almost constant in size. Oxygen yield per flash per cell was nearly constant whereas Emerson photosynthetic unit size increased in cells moved to the reduced incident light intensity.