Photosynthesis Research 18:133-161(1988) © Kluwer Academic Publishers, Dordrecht - Printed in the Netherlands Minireview Regulation of cyanobacterial pigment-protein composition and organization by environmental factors HAROLD RIETHMAN, GEORGE BULLERJAHN, K.J. REDDY & LOUIS A. SHERMAN University of Missouri, Division of Biological Sciences, Tucker Hall, Columbia, MO 65211, USA Received 30 September 1987; accepted 24 December 1987 Key words: chlorophyll-protein, cyanobacteria, iron stress, phycobilisome Abstract. The coordinate expression of stress-specific genes is a common response of all organisms to altered environmental conditions. In cyanobacteria, the physiological conse- quences of stress are often reflected in both the ultrastructure of the cell and in photosynthesis- related properties. This review will focus on the alterations in cyanobacterial pigment-protein organization which occur under different growth conditions, and how several molecular genetic aproaches are being used in this laboratory to investigate the regulatory mechanisms underlying these alterations. We will discuss in detail the response to iron starvation, and present a testable hypothesis for the mechanism of thylakoid reorganization mediated by this response. Abbreviations: ConA - concanavalin A, CP - chlorophyll-protein complex, LHCP - light harvesting chlorophyll protein, MSP - manganese-stabilizing protein I Introduction Environmental factors affecting cyanobacterial pigment-proteins The pigment systems of photosynthetic organisms have evolved to fit the local environments of the particular species. Land plants have evolved specialized chloroplasts containing copious amounts of LHCPII to harvest sunlight, whereas many algal species have evolved unusual carotenoid and Chl-like pigments to allow efficient light-harvesting at particular depths in the water or in special terrestrial environments. Cyanobacteria have evolved to fill nearly every imaginable ecological niche from symbiotic associations with fungi in antarctic sandstone to geothermal hot springs. Not surprising- ly, cyanobacterial pigments reflect this ecological diversity. Phycobilipro- teins and carotenoids are present in the various cyanobacterial light-harvest- ing systems which can absorb light from most regions of the visible spec-