Journal of Photochemistry and Photobiology B: Biology 64 (2001) 69–74 www.elsevier.com / locate / jphotobiol Light regulation of cyclic-AMP levels in the red macroalga Porphyra leucosticta a, b c a * ´ ´ Marıa Segovia , Francisco J.L. Gordillo , Pauline Schaap , Felix L. Figueroa a ´ ´ ´ Departamento de Ecologıa, Facultad de Ciencias, Universidad de Malaga, Malaga, Spain b Aquatic Systems Group, Agriculture and Environmental Sciences Division, Queen’ s University of Belfast, Belfast, UK c Department of Biochemistry, University of Dundee, MSI / WTB Complex, Dundee, UK Received 30 May 2001; accepted 26 August 2001 Abstract Total cyclic-39-59-adenosine monophosphate (cAMP) levels were measured in the gametophyte of the red macroalga Porphyra leucosticta under different light conditions in order to study its regulation by phytochrome or photosynthesis. cAMP levels were relatively low when samples were incubated in darkness, or exposed to red or far-red light. Irradiation with red1far-red light induced a moderate increase in cAMP levels, while white light induced a pronounced increase in cAMP levels. When incubated under increasing white light irradiance, cAMP levels closely followed the increase in photosynthetic oxygen evolution rate, suggesting a direct relationship between photosynthesis and cAMP accumulation. cAMP levels were not dependent on cellular ATP concentration, as inhibitors of ATP synthesis did not significantly affect cAMP levels in light. We conclude that cAMP depends on photosynthetic activity regardless of ATP synthesis and concentration or phytochrome activity.  2001 Elsevier Science B.V. All rights reserved. Keywords: cAMP; Macroalga; Photomorphogenesis; Photoreceptors; Photoregulation; Photosynthesis; Phytochrome 1. Introduction were suspected to co-chromatograph with authentic cAMP or to interfere with the cAMP binding protein in sensitive Cyclic AMP is a ubiquitous second messenger in cAMP isotope dilution assays [7]. Mass-spectrometric bacteria, eukaryotes, protists, fungi and metazoans, and methods provide greater specificity for cAMP measure- mediates a wide array of cellular responses to extracellular ments [8]. By using such methods, cell cycle-driven cAMP signals. oscillations were demonstrated in tobacco BY-2 cells. In the plant kingdom, studies on microalgae have These cAMP oscillations could be blocked by in- provided us with well documented functions for cyclic-39- domethacin, an inhibitor of prostaglandin synthesis, which 59-adenosine monophosphate (cAMP). cAMP mediates indirectly prevents prostaglandin stimulation of a mam- sexual fusion in Chlamydomonas [1] and the control of malian adenylyl cyclase [9,10]. cAMP has been identified circadian rhythms in Euglena gracilis [2]. Activities of in extracts of the intertidal red macroalga Porphyra adenylyl cyclases and cAMP phosphodiesterases, which umbilicalis by mass spectrometry [11]. Intertidal macro- respectively synthesise and degrade cAMP, were character- algae are sessile organisms subjected to strong fluctuations ised in microalgae [3–5] and a cAMP dependent protein in both light quantity and spectral light quality [12,13]. kinase gene was recently cloned from E. gracilis [6]. Light plays an essential role in controlling both plant In vascular plants, both the occurrence and possible physiology and morphology in two ways: (i) as a source of function of cAMP have been much disputed. cAMP levels, energy, and (ii) as an environmental signal acting on if present, are very low and impurities in plant extracts phytochrome or blue light photoreceptors to drive photo- morphogenesis [14–16]. Phytochrome is characteristically activated by red light and inactivated by far-red light [17]. *Corresponding author. Present address: School of Biology and Phytochrome-like proteins have been detected in both P . Biochemistry, Queen’s University of Belfast, 97 Lisburn Road, Belfast umbilicalis and Porphyra leucosticta [18]. Both cAMP and BT9 7BL, UK. Tel.: 144-2890-272-259; fax: 144-2890-236-505. E-mail address: m.segovia@qub.ac.uk (M. Segovia). cGMP have been implicated in the signal transduction 1011-1344 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S1011-1344(01)00218-4