Action spectra for chromatic adaptation in the blue-green alga Fremyella diplosiphon

Action spectra for chromatic adaptation in Fremyella diplosiphon Drouet have been determined using techniques previously described. Action maxima are at 540 nm, with a half-band width of 80 nm, for induction of phycoerythrin synthesis (green action) and at 650 nm, with a half-band width of 90 nm, for reversal of induction of phycoerythrin synthesis (red action). The red-action spectrum includes a secondary action band centered at ca. 360 nm. Red and green action overlap from 570 to 590 nm with an isosbestic point in the vicinity of 580 nm. Shoulders are present at 520 and 630 nm. Red light is more active than green light. The 540:650-nm quantum effectiveness ratio is 1:7. There is relatively little action of either kind in the blue. The 387:540 nm and 460:650-nm quantum effectiveness ratios are zero. These results contrast strongly with previous determinations in the same organism, with major activity indicated in the blue; they are consistent with the control of photomorphogenesis in the Cyanophyta by a master pigment, analogous to phytochrome.