Light regulation of cyclic-AMP levels in the red macroalga Porphyra leucosticta

Total cyclic-3'-5'-adenosine monophosphate (cAMP) levels were measured in t he gametophyte of the red macroalga Porphyra leucosticta under different li ght conditions in order to study its regulation by phytochrome or photosynt hesis. cAMP levels were relatively low when samples were incubated in darkn ess, or exposed to red or far-red light. Irradiation with red+far-red light induced a moderate increase in cAMP levels, while white light induced a pr onounced increase in cAMP levels. When incubated under increasing white lig ht irradiance, cAMP levels closely followed the increase in photosynthetic oxygen evolution rate, suggesting a direct relationship between photosynthe sis and cAMP accumulation. cAMP levels were not dependent on cellular ATP c oncentration, as inhibitors of ATP synthesis did not significantly affect c AMP levels in light. We conclude that cAMP depends on photosynthetic activi ty regardless of ATP synthesis and concentration or phytochrome activity. ( C) 2001 Elsevier Science B.V. All rights reserved.