Effects of PAR and high UVR on enzymes and other proteins involved in the function and protection of the photosynthetic apparatus of marine macroalgae.

Abstract

The changes in the quality and quantity of the solar radiation may affect photosynthetic organisms. An increase in irradiation of UVB of the solar radiation that reaches the earth’s surface due to thinning of the ozone layer, for instance, can cause destructive consequences to these photoautotrophs. Thus, like any other photoautotrophs, macroalgae are deemed to be affected and loss of these important biomass producers of the aquatic ecosystem may disrupt the primary productivity and the whole ecosystem integrity. However, the macroalgae have somehow developed protective mechanisms to ensure their survivality in the extreme environment.

In this study, short-term responses of five marine macroalgae, Solieria chordalis, Palmaria palmata, Laminaria digitata, Dictyota dichotoma and, Ulva lactuca to ultraviolet radiation (UVR) were investigated. The algae were irradiated for 5 h to a high UVR in combination with either low or high background photosynthetically active radiation (PAR) Four light regimes were created using cut-off filters: PAR, PAR+UVA, PAR+UVA+UVB or UVA+UVB. Recovery kinetics were also determined by incubating the irradiated algae in dim light for 18 h. Responses were evaluated on the basis of photosynthetic performance (i.e. Fv/Fm, rETRmax, á and Ik), photodamage or photoinactivation (i.e. via pigments analysis, total soluble proteins content, RuBisCo activity and its large subunit (LSU) composition, GAPDH activity and D1 protein content), and photoprotective mechanisms (i.e. via antioxidative enzymes activity, presence of stress proteins and non-photochemical quenching).

All of the algae examined were strongly inhibited by the high UV and high PAR. High tolerance to UVB was displayed by the algae at much lower UVB fluxes. Even though UVB generally caused damaging effects, some of the algae responded positively to UVB. Whilst the brown algae L. digitata and D. dichotoma collectively showed the highest inhibition, the green alga U. lactuca was the least affected and was well-prepared and well-adapted to the high light effect. The red algae S chordalis and P. palmata were also strongly inhibited but recovered more slowly than the rest of the algal classes.