Green-to-red photoconversion of GFPs in live cells. (a) Fluorescence microscopy of Phoenix Eco cells transiently expressing EGFP-N1 in green (upper row) and red (center row) channels. Bottom row represents an overlay of the green and red images. Numbers above images designate duration of blue light irradiation (1W/cm2) that induces green-to-red photoconversion. Note high heterogeneity of cells after 30 s of irradiation that results in different colors on the overlaid image. Scale bar, 20 µm. (b) Quantification of fluorescence changes in two selected individual cells—cell 1 (filled squares) and cell 2 (open triangles)—marked in a. (c, d) Redding efficiency normalized according to initial green fluorescence level for designated cell lines transiently expressing EGFP in cytoplasm (c) or mitochondria (d). Maximal (red columns), average (yellow columns) and minimal (green columns) responses are shown for each cell line. (e, f) Green-to-red photoconversion in a live button polyp, Zoanthus sp. (e) The Zoanthus specimen used in this work. (f) Confocal optical section through a tip of the native tentacle in green (left images) and red (center images) channels and their overlay (right images) before (upper row) and after (bottom row) photoconversion. Here, green fluorescence is characteristic of the ectoderm cells, whereas endoderm cells contain symbiotic algae Zooxantella, which resembles red spheres due to chlorophyll fluorescence. Local photoconversion was induced in the region marked by a white square using irradiation with 100% 488 nm laser line (0.15 W/cm2). Scale bar, 50 µm.