15N‐uptake, influenced by UV‐B radiation, and pattern of amino‐acid pools during akinete germination in Anabaena variabilis (Cyanobacteria)

In order to obtain better information on the nitrogen supply during the early germination period of Anabaena resting cells (akinetes) the uptake of 15N‐nitrate and 15N‐ammonium and changes in the amino acid pools were studied. Additionally, the influence of a UV‐B‐dose on the nitrogen uptake in germinating akinetes was investigated. Results indicate: (1) Ammonium was finally incorporated during a 48‐hours period after initiation of germination to a similar degree as nitrate, but follows different kinetics. (2) UV‐B radiation (0.95 W m−2, 0.5 to 5 hours) applied at the beginning of this period, did not have any (15N‐nitrate) or only minor (15N‐ammonium) influence on the nitrogen uptake (% 15N enrichment determined 48 h after initiation of germination). When a comparable UV‐B load was applied at the end of the 48‐hours (pre‐)germination period, a varying effect on the 15N‐accumulation during a subsequent 48‐hours period could be noticed: Whereas the nitrate uptake again remained uninfluenced, increasing accumulation of 15N‐ammonium took place, corresponding to the increasing UV‐B dose. (3) Pool patterns of amino acids/amides are different in akinetes and filament cells (filaments show a relatively higher content in glutamate, glutamine, serine and lower in arginine, asparagine and lysine). (4) During the 48‐hours (pre‐)germination period a transient increase in the proportion of some amino acids/amides was established, but the drastic proportionate decrease in the content of asparagine and arginine during the first 6 to 12 hours after initiation of germination was the most conspicuous effect. This observation is discussed in connection with the nitrogen mobilisation from the cyanophycin storage of the cells.