Uptake of amino acids by the aquatic resurrection plant Chamaegigas intrepidus and its implication for N nutrition

Chamaegigas intrepidus is a poikilohydric aquatic plant that lives in rock pools on granitic outcrops in Central Namibia. The pools are filled intermi ttently during the summer rains, and the plants may pass through up 20 rehy dration/dehydration cycles during a single wet season. Rehydrated plants al so have to cope with substantial diurnal fluctuations in the pH and extreme nutrient deficiency. Ammonium concentrations are normally around 30 mu M. Additional nitrogen sources are amino acids. Total free amino acids are up to 15 mu M with glycine and serine as the predominant amino acids. Experime nts on uptake of radiolabelled amino acids into roots of C. intrepidus show ed high affinity (K-M = 16 mu M) and low-affinity (K-M = 159 mu M) uptake s ystems. The K-M of the high-affinity system is well in accordance with the free amino acid concentration found in the water of the pools. We conclude that amino acids, predominantly glycine and serine, can be utilised by C. i ntrepidus in its natural habitat. Since glycine uptake showed a strong redu ction at pH 10, nitrogen uptake from glycine or serine should occur mainly in the morning when the pH of the pool water is slightly acid. Further expe riments with N-15-labelled ammonium in combination with non-labelled glycin e demonstrated high delta(15)N values in plant tissues. Under experimental conditions C. intrepidus preferred ammonium as a nitrogen source. The impli cation of amino acids for nitrogen nutrition of C. intrepidus may depend on the relation of inorganic and organic nitrogen available in the pool water and the preferential utilisation of one or the other nitrogen source may c hange during the day corresponding with pH changes in the water.