Blue light and UV-A radiation control the synthesis of mycosporine-like amino acids in Chondrus crispus (Florideophyceae)

The induction of UV-absorbing compounds known as mycosporine-like amino aci ds (MAAs) by red, green, blue, and white light (43% ambient radiation great er than 390 nm) was examined in sublittoral Chondrus crispus Stackh, Fresh collections or long-term cultures of sublittoral thalli, collected from Hel goland, North Sea, Germany, and containing no measurable amounts of MAAs, w ere exposed to filtered natural radiation for up to 40 days. The MAA palyth ine (lambda (max) 320 mn) was synthesized hi thalli in blue light to the sa me extent observed in control samples in white light. In contrast, thalli i n green or red light contained only trace amounts of MAAs. After the growth and synthesis period, the photosynthetic performance of thalli in each tre atment, measured as pulse amplitude modulated chlorophyll fluorescence, was assessed after a defined W dose in the laboratory. Thalli with MAAs were m ore resistant to UV than those without, and exposure to UV-A+B was more dam aging than UV-A ill that optimal (F-v/F-m) and effective (phi (II)) quantum yields were lower and a greater proportion of the primary electron accepto r of PSII, Q, became reduced at saturating irradiance. However, blue light- grown thalli were generally more sensitive than white light control samples to W-A despite having similar amounts of MAAs. The most sensitive thalli w ere those grown in red light, which had significantly greater reductions in F-v/F-m and phi (II) and greater Q reduction. Growth under W radiation alo ne had been shown previously to lead to the synthesis of the MAA shinorine (lambda (max) 334 nm) rather than palythine. In further experiments, we fou nd that preexposure to blue light followed by growth in natural UV-A led to a 7-fold increase ill the synthesis of shinorine, compared with growth in UV-A or UV-A+B without blue light pretreatment. We hypothesize that there a re two photoreceptors for MAA synthesis in C. crispus, one for blue light a nd one for UV-A, which can act synergistically. This system would predispos e C. crispus to efficiently synthesize UV protective compounds when radiati on levels are rising for example, on a seasonal basis. However, because the UV-B increase associated with artificial ozone reduction will not be accom panied by an increase in blue light, this triggering mechanism will have li ttle additional adaptive value in the face of global change unless a global UV-B increase positively affects water column clarity.