The regulatory role of polyamines in structure and functioning of the photosynthetic apparatus during photoadaptation

In this contribution we describe the changes in structure and functioning o f the photosynthetic apparatus of the unicellular green alga Scenedesmus ob liquus induced by inhibition or induction of polyamine biosynthesis. The sy nthesis or inhibition is controlled by white Light of low and high intensit ies, as well as by blue and red irradiation. We observe that a decrease of the intracellular putrescine level and, Vice versa, an increase of spermine , indicated by a raised ratio of spermine to putrescine, simulate a low-lig ht photoadapted photosynthetic apparatus. Action spectra of the spermine/pu trescine ratio compared with action spectra on characteristics of photoadap tation, e.g., chlorophyll biosynthesis, or the rate of primary photochemist ry and electron transport, show that the photoreceptors for both the adapta tion of the photosynthetic apparatus to low-light conditions and for the re gulation of the spermine/putrescine ratio are, at least. very. similar. We show that the photoreceptor is primarily a blue-light receptor with a super imposed red-light receptor that absorbs around 680 nm. (C) 1999 Elsevier Sc ience S.A. All rights reserved.