Comparative in vivo fluorescent spectrophotometric analyses of cells expressing EGFP, TtsfGFP, and sfGFP. Tetrahymena clones carrying TtsfGFP-, sfGFP-, and EGFP-expressing constructs were grown until the mid-logarithmic phase and cell density adjusted to 3 × 105 cells/mL. The cells were induced with 2 μg/mL of CdCl2. In vivo fluorescence spectrophotometric analyses were performed every 30 min at 488 nm excitation and 510 nm emission. The difference in emission between TtsfGFP, sfGFP, and EGFP began at 60 min and continued until 180 min. At the end of the time interval, TtsfGFP clones were found to emit ~2.2 fold and ~4 fold more fluorescence than sfGFP and EGFP, respectively.