Ammonium and UV Radiation stimulate the accumulation of mycosporine like amino acids in Porphyra columbina (Rhodophyta) from Patagonia, Argentina

Abstract

The combined effects of ammonium concentration and UV radiation on the red alga Porphyra columbina (Montagne) from the Patagonian coast (Chubut, Argentina) was determined using shortterm (less than a week) experimentation. Discs of P. columbina were incubated with three ammonium concentrations (0, 50, and 300 lM NH4Cl) in an illuminated chamber (PAR 5 300 lmol photons . m 2 . s 1 , UVA 5 15W. m 2 , UVB 5 0.7W. m 2 ) at 151 C. Algae incubated at 300 lM ammonium showed a significant increase (Po0.05) in the concentration of mycosporine-like amino acids (MAAs) compared with the initial value or with the other ammonium treatments. The increase of MAAs was, however, a function of the quality of irradiance received, with a higher increase in samples exposed to UVA compared with UVB (29% and 5% increase, respectively). However, UVB radiation was more effective in inducing MAA synthesis per unit energy received by the algae. Samples exposed to PAR only had an intermediate increase in MAA concentration of 16%. Chl a concentration decreased through the incubation with the greatest decrease at high ammonium concentration. Phycobiliprotein (BP) decreased through time with the smallest decrease occurring at high ammonium concentration. Photoinhibition (as a decrease of optimal quantum yield) was significantly greater under nitrogen-deprived conditions than that under replete ammonium levels. Maximal gross photosynthesis (GPmax), as oxygen evolution, and maximal electron transport rate (ETRmax), as chl fluorescence, increased with the ammonium concentration. Positive relationships between maximal GP or ETR and pigment ratios (BP/chl a and MAAs/chl a) and negative relationships with chl a concentration were found. Key index words: ammonium; biliproteins; chl fluorescence; mycosporine-like amino acids; photosynthetic activity; Porphyra; quantum yield; UV radiation Abbreviations: a, area; A, absorbance; a, photosynthetic efficiency; BP, phycobiliprotein; DIN, dissolved inorganic nitrogen DW, dry weight; ETR, electron transport rate; Fo, initial fluorescence in the dark-adapted state (all reaction centers are open, oxidized); Fm, maximal fluorescence in the darkadapted state (all reaction centers are closed, reduced); Fm0 , the same for the light-adapted state; Fv/Fm, optimal or maximal quantum yield; FW, fresh weight; GP, gross photosynthetic rate; GPmax, gross photosynthetic rate at light saturation; P, PAR; PA, PAR þ UVA; PAB, PAR þ UVA þ UVB; PAM, pulse amplitude modulated fluorescence; PC, phycocyanin; PE, phycoerythrin; FPSII, effective quantum yield as chl fluorescence; FO2, photosynthetic quantum yield as oxygen evolution; Rd, darkrespiration rate; UVA, ultraviolet A (k 5 315– 400 nm); UVB, ultraviolet B (k 5 280–315 nm); UVR, ultraviolet radiation (k 5 280–400 nm)