Effect of UV Irradiance on Utilization of Inorganic Nitrogen by the Antarctic Diatom Odontella weissflogii (Janisch) Grunow

Abstract

Abstract: The impact of UV‐B irradiation on unialgal cultures of the temperate marine diatom Odontella sinensis and of the Antarctic Odontella weissflogii was tested under controlled laboratory conditions. Uptake rates of inorganic nitrogen by Odontella sinensis were more affected by UV‐B radiation than those of Odontella weissflogii. Utilization of 15N‐ammonium was reduced after 3 h of UV‐B exposure. Values of Km from several marine phytoplankton species were estimated from algae not exposed to UV‐B and from those after 3 h of UV‐B radiation. Calculation of Lineweaver‐Burk plot showed, under UV‐B stress, a noncompetitive inhibition for 15NH+4 uptake and a competitive inhibitory effect for 15NO−3 by Odontella weissflogii. The damage to 15NH+4 uptake by UV‐B was more pronounced under red than blue light; a contradictory result was obtained for 15NO−3 utilization by Odontella weissflogii. Reduction of the pigments by UV‐B under white light was dependent on the exposure time; a strong depression of the contents of chlorophyllide a, chlorophyll c, diatoxanthin and the fucoxanthins was found. Contents of the chlorophylls are markedly affected by UV‐B under red light whereas the chlorophyll a concentration is enhanced in blue and green light. UV‐B exposure in conjunction with blue and green light led to a reduction of the protein content and an increase in the amino acid contents. The pattern of pool sizes of free amino acids varied after UV‐B exposure. UV‐A irradiance had no effect. The possible targets of UV‐B irradiation on the uptake system of inorganic nitrogen are discussed in detail. Adaptation to the environmental conditions, e.g. via synthesis of UV stress proteins or mycosporine‐like amino acids, were also considered.