Effect of irradiance on the physiology and ultrastructure of the marine cryptomonad, Cryptomonas strain Lis (Cryptophyceae)

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Abstract
Cryptomonas strain Lis was grown under HL [high light] (260 .mu.E[Einsteins]/m2 per s) and LL [low light] (10 .mu.E/m2 per s) conditions, and growth, photosynthetic pigments, photosynthesis, intrathylakoidal width, starch and compensation point were compared. On a per cell basis, cells grown under LL contained twice as much chlorophyll a and chlorophyll c as those grown under HL conditions. Phycoerythrin, however, showed a 6-fold increase when light intensity decreased from 260 .mu.E/m2 per s to 10 .mu.E/m2 per s. Both chloroplast area and intrathylakoidal width were increased to accommodate for the increase in photosynthetic pigment in LL cells. The increase in photosynthetic pigment under LL conditions was accompanied by an increase in photosynthetic rate per cell, but the intensity at which photosynthesis ceases to be light-limited (Ik) and the compensation point were markedly reduced. Starch content and growth rate of HL cells were about 4 times as high as LL cells. Cryptomonas strain Lis apparently adapts to LL level by an increase in the number and size of the photosynthetic unit.