PHOTOSYNTHETIC PRODUCTION OF HYDROGEN-PEROXIDE BY ULVA-RIGIDA C-AG (CHLOROPHYTA)

Production of hydrogen peroxide has been found in Ulva rigida (Chlorop hyta). The formation of H2O2 was light dependent with a production of 1.2 mu mol . g FW-1. h(-1) in sea water (pH 8.2) at an irradiance of 7 00 mu mol photons m(-2). s(-1). The excretion was also pH dependent: i n pH 6.5 the production was not detectable (< 5 nmol . g FW-1. h(-1)) but at pH 9.0 the production was 5.0 mu mol . g FW(-1)h(-1). The produ ction of H2O2 was totally inhibited by 3-(3,4-dichlorophenyl)-1,1-dime thylurea (DCMU). The ability of U. rigida growing in tanks (750 1) und er a natural light regime to excrete H2O2 was checked and found to be seven times higher at 08.00 hours than other times of the day. The H2O 2 concentration in the cultivation tank (density: 2 g FW . 1(-1)) reac hed the highest value (3 mu M) at 11.00 hours. Photosynthesis was not influenced by H2O2 formation. The H2O2 is suggested to come from the M ehler reaction (pseudocyclic photophosphorylation). With an oxygen evo lution of 120 mmol . g FW(-1)h(-1) at pH8.2 and 90 mmol . g FW-1. h(-1 ) at pH 9.0, 0.5% and 2.7% of the electrons were used for extracellula r H2O2 production. The H2O2 production is sufficiently high to be of p hysiological and ecological significance, and is suggested to be a par t of the defence against epi- and endophytes.