Photosynthesis of Prochloron as affected by environmental factors

The effects of light intensity, pH, temperature, and UV irradiation on the photosynthetic rate of Prochloron isolated from the ascidian host Lissoclin um patella, collected from Palau, were examined. Photosynthesis increased w ith light intensity with saturation at 500 mu lmol/m(2) per second. It was maximum at pH 8 to 9 but almost completely suppressed below pH 7. The optim um temperature was 35 degrees to 40 degreesC, but the photosynthesis was ab sent at less than or equal to 20 degreesC and at 45 degreesC. It was recove red when the symbiont was transferred from 1 hour of incubation at less tha n or equal to 20 degreesC to 35 degreesC but not when transferred from incu bation at 45 degreesC. Ultraviolet irradiation severely inhibited the photo synthesis of Prochloron in isolation but not in vivo. This protection was b rought about by the tunic covering the ascidian colony, which contains UV-a bsorbing mycosporine-like amino acids. These results indicate that the char acteristic condition of the tropical marine environment largely determines the ecological distribution of Prochloron, and the ascidian tunic protects the organism from UV radiation.