The Photosynthetic Function of Pigments other than Chlorophyll

Abstract

Ever since men noticed yellowing autumnal leaves, or gathered brown, red, or blue algae, they must have speculated as to the meaning of these colors. Scientific interest became the more acute as physiologists realized the universal distribution of chlorophyll in photosynthetic systems, and its undoubted importance as the primary light absorber. But the other are also widespread: one (f3-carotene) is almost always present, and there are usually several others found in every photosynthetic system. Their distribu­ tion is remarkably parallel to phylogenetic lines. What are these other doing? Are they accidental and indifferent, merely happening to absorb light (like hemoglobin) without this absorption having much physiological function? Are they helpful or wasteful filters, by their absorption protecting other systems from injurious or useful radiation? Are they, perhaps, themselves injurious, inducing photodynamic or photo­ oxidative effects? Do they collaborate with chlorophyll, optically or chemical­ ly, thereby qualifying as truly accessory? Or are they completely inde­ pendent, supplementary light absorbers, with their own parallel complement of enzyme systems, able to carry out photosynthesis without the interven­ tion of chlorophyll? Indeed, do they sometimes take over the major absorb­ ing function, subordinating chlorophyll itself to an or indifferent position? This chapter attempts to summarize current information on the role of the so-called accessory pigments in photosynthesis. There has been brief mention of these in various recent reviews (1 to 5), and Rabinowitch has given his usual excellent discussion of the problem [(6), chaps. IS, 17; (7), chaps. 21-24, 30]. Several comprehensive descriptions of the pigments, with­ out much emphasis on their function, have appeared lBoresch (8); Cook (9); Strain, (10, 11, 12)]. The present author has assembled some of the back­ ground, as well as new material, especially on the algae, in a forthcoming chapter [Blinks (13)]. No attempt is made here to include photosynthetic bacteria, which will be covered in Volume 8 of the Annual Review of Micro­ biology.