FIGURE 6.

Intracellular oxygen concentrations of a Chara corallina cell (A) and a cell of an orange fruit (B). In addition to the modulated green light used to excite the sensor, both cell types were temporarily exposed to unmodulated blue light to stimulate photosynthesis. In the photosynthesis competent Chara cell, the internal oxygen concentration rapidly increases when the blue light source was switched on. In the nonphotosynthetic orange cell, blue light had no effect on the internal oxygen concentration. The temperature was 23°C.