Control of Phycoerythrin Synthesis during Chromatic Adaptation

Abstract

Chromatic adaptation is the process by which blue-green algae alter the rates of biliprotein synthesis in response to changes in the color of available light. We have examined the control of phycoerythrin synthesis during the early stages of chromatic adaptation in FremyeUla diplosiphon using fluo-rescence spectroscopy and 35S-labeUng of polypeptides. Phycoerythrin synthesis begins within 45 to 90 minutes after transfer of cells from red to green light, but is blocked by rifamycin. Transfer of ceDls from green to red light stops phycoerythrin synthesis with a ti/2 = 45 minutes, as does the addition of rifamycin in green lght. Transfer from green light to darkness slows but does not stop phycoerythrin synthesis. Gel electrophoresis of labeled polypeptides, both soluble and membrane-bound, shows that the synthesis of some polypeptides other than phycoerythrin are also affected by changes in light. These data suggest that chromatic adaptation involves gene regulation at the transcriptional level. Blue-green algae (Cyanophytes) contain phycobiliprotein pigments which serve as the major accessory pigments for photosyn-thesis. Cyanophytes characteristically synthesize PC3 and APC. In addition, many species also synthesize PE. Among those species which contain PE, some synthesize different relative proportions of PE and PC depending upon the spectrum of available light. This is called complementary chromatic adaptation (2). Although it has been shown to occur in a wide variety of algae (4, 13), recent studies of chromatic adaptation have been carried out primarily with the species Tolypothrix tenuis and Freymyella diplosiphon. In both of these organisms adaptation is achieved primarily by quantitatively or qualitatively altering the synthesis of PE, although the PC content is also affected (1, 7). Chromatic adaptation involves the synthesis of new biliproteins (1). The time course of chromatic adaptation has been examined over periods of many hours to several days for both Tolypothrix (12) and Freymyella (1, 8). Although these studies have elucidated the overall changes in pigment synthesis which accompany adaptation , previously employed methods have not been sufficiently sensitive to reveal the early events in this process which would be expected to give some insights to the mechanisms controlling the synthesis of the phycobiliproteins. We have taken advantage of the sensitivity of fluorescence spectroscopy to examine early stages of PE production during chromatic adaptation by Freymyella. Gel electrophoresis of proteins labeled during adaptation was used to confirm the spectro-'