Relationships among cell chlorophyll content,photosystem II light-harvesting and the quantum yield for oxygen production in Chlorella

Cells of the green alga Chlorella vulgaris were grown under conditions where total Chl/cell varied by a factor of almost 80; from 0.02 fmol/cell to nearly 1.6 fmol/cell. The change in Chl/cell was accomplished by an approximately 11-fold increase in RCII/cell along with a 7-fold increase in Chl/RCII. The effective absorption cross section per RCII at 596 nm varied by a factor of 6, increasing with Chl/cell from a minimum of 20 A² to a maximum of 116 A². In contrast, over the same range of Chl/cell, the quantum requirement for O₂ production remained relatively constant at 10.4±1.8 quanta absorbed/O₂ evolved. The results are well described by a simple model in which changes in Chl/cell are produced by coordinated changes in reaction center and light-harvesting complexes. The model predicts that between 20 and 40% of the light-harvesting chlorophyll-protein complexes commonly assigned to PSII, do not function as antenna for PSII.This paper is dedicated to the memory of Warren L. Butler, a pioneer in the field of photobiology. His creativity and innovativeness as a scientist were matched only by his patience as a mentor.