Urea: a nitrogen source for the aquatic resurrection plant Chamaegigas intrepidus Dinter

Chamaegigas intrepidus Dinter is a poikilohydric aquatic plant that lives i n rock pools on granite outcrops in central Namibia. The pools are filled w ith water only intermittently during the wet season, and the plants may pas s through up to 20 rehydration/dehydration cycles during the summer rains. The potential nitrogen sources for the rehydrated plants are ammonium, whic h is only present at 10-20 mu M, amino acids, particularly glycine, and ure a, which is generally present at 20-30 mu M. We show that urea can be utili sed by plants in the field through the presence of urease in the sediments of the rock pools. Urease activity is higher in non-submerged than in subme rged sediments, and it can survive 6 months of complete dryness at temperat ures up to 60 degrees C. Experiments with [C-14]urea under laboratory condi tions show that the roots of C. intrepidus are unable to take up urea; whil e N-15-nuclear magnetic resonance experiments show that [N-15]urea is only metabolised to labelled glutamine and glutamate after ammonium has been rel eased by the action of urease. Thus urease plays a vital role in allowing u rea to be utilised as a major N source in this nutrient-limited aquatic eco system.