Morphology, growth, photosynthesis and pigments in Laminaria ochroleuca (Laminariales, Phaeophyta) under UV radiation

Young sporophytes of Laminaria ochroleuca were exposed in the laboratory either to a full light spectrum or to light depleted of only ultraviolet-B radiation (UVB) or of the whole ultraviolet radiation (UVR) using cutoff glass filters. The plants were grown under 16:8 h light-dark cycles with 6 h additional UV exposure in the middle of the light phase. Effective quantum yield of photosystem II (ΔF/Fm′) was measured daily, 1 h before UV exposure, at 2 and 5 h cumulative UV exposure and at 1 and 4 h after UV exposure. Growth was measured using two methods in separate experiments. In the first, a scanner with image analysis software was used to measure surface area every 3 days for 4 weeks. In the second, a growth chamber with online video measuring technique was used to measure growth every 10 min for 2 weeks. Pigments were measured at the end of the experiments. During the first day of UV exposure, the photosynthetic yield of plants exposed to photosynthetically active radiation (PAR) + ultraviolet-A radiation (UVA) and PAR + UVA + UVB was significantly reduced but was able to recover 1 h after the end of UV exposure. An increasing mean ΔF/Fm′ during UV exposure showed partial acclimation of photosynthesis in young sporophytes in the course of several days. However, a higher growth rate was observed in plants exposed to PAR alone, whereas reduced growth and damaged tissue were observed in plants exposed to UVR. Similarly, a lower content of all pigments was measured in thalli exposed to PAR + UVR. The result shows that acclimation of photosynthesis could underestimate the negative effect of this stress factor. Growth, as an integrative process, is a better parameter to explain ecophysiological performance at organism level. It was shown that growth and morphology of young sporophytes of L. ochroleuca are susceptible to UV damage, which could effectively limit the upper distributional range of this species

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 acids (MAAs) by red, green, blue, and white light (43% ambient radiation greater than390 nm) was examined in sublittoral Chondrus crispus Stackh. Fresh collections or long-term cultures of sublittoral thalli, collected from Helgoland, North Sea,Germany, and containing no measurable amounts of MAAs, were exposed to filtered natural radiation for up to 40 days. The MAA palythine (max 320 nm) wassynthesized in thalli in blue light to the same extent observed in control samples in white light. In contrast, thalli in green or red light contained only trace amounts ofMAAs. After the growth and synthesis period, the photosynthetic performance of thalli in each treatment, measured as pulse amplitude modulated chlorophyllfluorescence, was assessed after a defined UV dose in the laboratory. Thalli with MAAs were more resistant to UV than those without, and exposure to UV-A+B wasmore damaging than UV-A in that optimal (Fv/Fm) and effective (II) quantum yields were lower and a greater proportion of the primary electron acceptor of PSII,Q, became reduced at saturating irradiance. However, blue light-grown thalli were generally more sensitive than white light control samples to UV-A despite havingsimilar amounts of MAAs. The most sensitive thalli were those grown in red light, which had significantly greater reductions in Fv/Fm and II and greater Qreduction. Growth under UV radiation alone had been shown previously to lead to the synthesis of the MAA shinorine (max 334 nm) rather than palythine. In furtherexperiments, we found that preexposure to blue light followed by growth in natural UV-A led to a 7-fold increase in the synthesis of shinorine, compared with growthin UV-A or UV-A+B without blue light pretreatment. We hypothesize that there are two photoreceptors for MAA synthesis in C. crispus, one for blue light and onefor UV-A, which can act synergistically. This system would predispose C. crispus to efficiently synthesize UV protective compounds when radiation levels are rising,for example, on a seasonal basis. However, because the UV-B increase associated with artificial ozone reduction will not be accompanied by an increase in blue light,this triggering mechanism will have little additional adaptive value in the face of global change unless a global UV-B increase positively affects water column clarity

Solar ultraviolet radiation affects the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase and the composition of photosynthetic and xanthophyll cycle pigments in the intertidal green alga Ulva lactuca L.

In this study the effect of solar UV radiation on thephysiology of the intertidal green macroalga Ulva lactuca L.was investigated. A natural Ulva-community at the shoreof Helgoland was covered with screening foils, excludingUV-B or UV-B + UV-A from the solar spectrum. In the sampledmaterial, changes in the activity and concentration ofRubisCO, and the concentration of photosynthetic andxanthophyll cycle pigments were determined. Exclusionof UV-radiation from the natural solar spectrum resultedin an elevated overall activity of RubisCO, related to anincrease in its cellular concentration. Among the photosyntheticpigments, lutein concentration was substantially elevatedunder UV exclusion. In addition, marked UV effects on thexanthophyll cycle were found: exclusion of solar UV-radiation(and particularly UV-B)resulted in an increased ratio ofzeaxanthin concentration to the total xanthophyll content,indicating adverse effects of UV-B on the efficiency ofphotoprotection under high irradiances of PAR. The resultsconfirm a marked impact of present UV-B levels on macroalgalphysiology under field conditions