Oxidative stress and enzymatic scavenging of superoxide radicals induced by solar UV-B radiation in &lt;i&gt;Ulva&lt;/i&gt; canopies from southern Spain

Kai Bischof,Anita G.J Buma,Paul J Janknegt,Jan W Rijstenbil,Anneke M Breeman,Gloria Peralta

doi:10.3989/scimar.2003.67n3353

Abstract

The generation of reactive oxygen species (ROS) and scavenging of the superoxide radical by superoxide dismutase (SOD) was studied in mat-like canopies of the green macroalga Ulva rotundata Bliding in a tidal brine pond system in southern Spain. Artificial canopies were covered with different cut-off filters, generating different radiation conditions. ROS and SOD were assessed after three days of exposure. ROS induced lipid peroxidation depended on the position of individual thalli within the canopy and on radiation conditions. Samples exposed to the full solar spectrum were most affected, whereas samples either exposed to photosynthetically active radiation (PAR) alone or UV radiation without PAR exhibited fewer peroxidation products. The activity of SOD appeared to be controlled by the impinging UV-A and UV-B radiation and also increased in response to oxidative stress. The results provide evidence for additive effects of high PAR and UV-B under field conditions and support the previously proposed hypothesis that UV-B effects are mediated by an inhibition of the xanthophyll cycle, which increases ROS production and, consequently, causes oxidative damage to components of the photosynthetic machinery, such as proteins and pigments.

Highlights

In eutrophic shallow coastal zones, Ulva species often cause green tides
Previous studies have shown the importance of canopy arrangement for maintaining high production rates of algal assemblages within these highly eutrophic systems (Pérez-Lloréns et al, 1996; Hernández et al, 1997)
The UV-B induced impairment of violaxanthin de-epoxidation has previously been demonstrated in isolated chloroplasts and intact leaves of higher plants (Pfündel et al, 1992), and for macroalgae under field conditions (Bischof et al, 2002a, b)

Summary

Introduction

In eutrophic shallow coastal zones, Ulva species often cause green tides. Thalli occur in dense, multilayered mats floating on the water surface (Hernández et al, 1997; Vergara et al, 1997, 1998). The top layer is regularly exposed to high solar radiation, whereas the shaded layers receive reduced light intensities (Vergara et al, 1997, 1998) These so called Ulva mats are frequently observed within soft bottom habitats along the shallow coastal zones of southern Spain. In the same study it was proposed that under field conditions the combination of high irradiance of photosynthetically active radiation (PAR) and UV-B radiation results in the loss of photosynthetic proteins and pigments, probably due to a high production of reactive oxygen species (ROS) in photosynthesis This was indicated by an impaired non-photochemical quenching (reflecting heat dissipation) and reduced activity of the xanthophyll cycle. The UV-B induced impairment of violaxanthin de-epoxidation has previously been demonstrated in isolated chloroplasts and intact leaves of higher plants (Pfündel et al, 1992), and for macroalgae under field conditions (Bischof et al, 2002a, b)

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Results

Discussion

Conclusion