Transcript accumulation of cynA (A and D), ntcA (C) and cynS (B, E, and F), in Prochlorococcus sp. MED4 (A to C), Synechococcus sp. WH8102 (D and E), and Synechococcus sp. WH7803 (F) cells grown on ammonium or on alternative N sources or deprived of combined N for 3, 6, 9, and >12 h after resuspension in fresh medium. The data are log2 of median values of three replicates, normalized to their initial transcription level, with 25th to 75th percentiles.