Impact of UV-B radiation on 15N-Ammonium and 15N-Nitrate uptake by Haematococcus lacustris (volvocales) II. The influence of a recovery period

Abstract

Summary The influence of UV-B irradiation (280–320 nm; 0.5 to 5 hours; 1.25 Wm −2 ) applied at the beginning of a 12 hours polychromatic irradiated («white light recovery») period (8 Wm −2 PAR) on the accumulation of 15 N-ammonium and 15 N-nitrate, the content of protein and amino acids/amides was investigated in different developmental stages (flagellates/aplanospores) and pre-cultivation variants (N-supplied/N-starved) of the freshwater green alga Haematococcus lacustris . In a further series of experiments the consequences of a white light recovery period, extended to 24 hours, on the UV-B influenced 15 N-accumulation was examined. Main results indicate: (1) The 12 hours recovery period does not abolish the uptake inhibition by UV-B, but lowers significandy the scope of it (i.e. the decrease of the N-accumulation; exception: N-starved (predark, -N) precultivated flagellates). (2) The cell type specific UV-B dose dependent course of the inhibition was similar to that without a recovery period (stronger in flagellates than in aplanospores). (3) An extension of the recovery period to 24 hours altered drastically the response of the flagellates (stimulated 15N uptake after UV-B irradiation, dose-dependent) but not in the aplanospores. (4) Proteins and pools of free amino acids/amides were specific influenced by the UV-B treatment and the recovery period, respectively. Also the relative content in single amino acids changed differendy on the UV impact, dependent on cell type, pre-treatment and if a recovery was included or not. Also without mentioning the UV-B impact, significant differences in the content of single amino acids were observed between flagellates and aplanospores: Arginine and glutamate were higher in aplanospores, whereas the opposite was found for serine.