XVI International Botanical Congess

The ammonium uptake rates were measured under nitrogen-limited and -sufficient conditions. Uptake rates of batch (BC) and semi-continuously (SC) cultured cells (0.25 umax) grown at 23 C were measured using 15N-labelled ammonium and by monitoring ammonium disappearance. The exponential phase BC cells had average C/N g-atom ratio of 6.1 (n=3, sd=0.2) and average C/chl a ratio of 47 (sd=1.3) while SC grown cells had average C/N g-atom ratio of 28.2 (n=3, sd=3.1) and average C/chl a ratio of 430 (sd=1.5). Average uptake rates of BC cells at 30 and 60 min after ammonium addition were 6.2 pg cell-1 h-1 (sd=0.3) and 4.7 pg cell-1 h-1 (sd=1.0), respectively while rates of the SC cells at 30 and 60 min were 5.4 pg cell-1 h-1 (sd=0.9) and 2.8 pg cell-1 h-1 (sd=0.4), respectively.