SymbioticAiptasia pulchella and freshly isolated zooxanthellae were incubated in NaH¹⁴CO₃ and NH₄Cl for 1 to 240 min, and samples were analysed by reverse-phase high-performance liquid chromatography (HPLC) and an online radiochemical detector. NH₄⁺ was first assimilated into¹⁴C-glutamate and¹⁴C-glutamine in the zooxanthellae residing inA. pulchella. The specific activities (dpm nmol⁻¹) of¹⁴C-glutamate and¹⁴C-glutamine in vivo, were far greater in the zooxanthellae than in the host tissue, indicating that NH₄⁺ was principally incorporated into the glutamate and glutamine pools of the zooxanthellae.¹⁴C-α-ketoglutarate was taken up from the medium by intactA. pulchella and assimilated into a small amount of¹⁴C-glutamate in the host tissue, but no¹⁴C-glutamine was detected in the host fraction. The¹⁴C-glutamate that was synthesized was most likely produced from transamination reactions as opposed to the direct assimilation of NH₄⁺. The free amino acid composition of the host tissue and zooxanthellae ofA. pulchella was also measured. The results presented here demonstrate that NH₄⁺ was initially assimilated by the zooxanthellae ofA. pulchella.

Authors and Affiliations

1. School of Biological Sciences, Building A08, University of Sydney, Sydney 2006, New South Wales, Australia, , , , , , AU

   R. Swanson & O. Hoegh-Guldberg

Received: 3 February 1997 / Accepted: 24 October 1997

Reprints and permissions