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.

Abstract

The effect of solar UV radiation on the physiology of the intertidal green macroalga Ulva lactuca L. was investigated. A natural Ulva community at the shore of Helgoland was covered with screening foils, excluding UV-B or UV-B + UV-A from the solar spectrum. In the sampled material, changes in the activity and concentration of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), and the concentration of photosynthetic and xanthophyll cycle pigments were determined. Exclusion of UV radiation from the natural solar spectrum resulted in an elevated overall activity of Rubisco, related to an increase in its cellular concentration. Among the photosynthetic pigments, lutein concentration was substantially elevated under UV exclusion. In addition, marked UV effects on the xanthophyll cycle were found: exclusion of solar UV radiation (and particularly UV-B) resulted in an increased ratio of zeaxanthin concentration to the total xanthophyll content, indicating adverse effects of UV-B on the efficiency of photoprotection under high irradiances of photosynthetically active radiation. The results confirm a marked impact of present UV-B levels on macroalgal physiology under field conditions.

Biological weighting function for xanthophyll de‐epoxidation induced by ultraviolet radiation

“…Among these, the formation of de-epoxidated xanthophylls, correlated with the development of NPQ (Demmig-Adams 1990, Horton et al 1994), has been described as an effective protective mechanism under severe PAR (for review Müller et al 2001) and UVR exposure (Götz et al 1999). However, the role of UVR in the stimulation of the xanthophyll de-epoxidation is still unclear (Bischof et al 2002, Döhler and Haas 1995, Döhler and Hagmeier 1997, Goss et al 1999, Mewes and Richter 2002, Pfündel et al 1992, Zudaire and Roy 2001. Our data show that in N. gaditana exposed to 48 different spectral treatments, the de-epoxidation of V to Z, through the intermediate A, occurs under PAR but is even greater under PAR þ UVR exposure.…”

“…Excitation pressure could be increased by UVR inhibition through decreased dissipation of reductant and adenosine 5 0 -triphosphate (Neale et al 1993). The latter may occur as UVR damages 'downstream' components of the photosynthetic pathway, for example, through lower activity of Rubisco (Bischof et al 2002, Lesser et al 1996, Nogués and Baker 1995, Vu et al 1982. In any case, the inhibition of photosynthesis by UVR exposure is relatively greater than the increase in de-epoxidation.…”

“…Previous results suggest this may be the case for studies of the effect of UVR on xanthophyll de-epoxidation. It has been reported that UVR can decrease de-epoxidation in algae and higher plants (Bischof et al 2002, Mewes and Richter 2002, Pfü ndel et al 1992, by inhibiting the V-deepoxidase enzyme (Pfü ndel et al 1992) as well as increasing the epoxidation activity (Mewes and Richter 2002). Conversely, increased xanthophyll de-epoxidation has been described in cultured and natural samples of phytoplankton exposed to UVR under controlled conditions (Dö hler and Haas 1995, Dö hler and Hagmeier 1997, Goss et al 1999, Zudaire and Roy 2001, while no differences were observed between cultures of Gymnodinium breve exposed to PAR only and PAR þ UVR treatments under natural sunlight (Evens et al 2001).…”

Exposure to ultraviolet radiation delays photosynthetic recovery in Arctic kelp zoospores

“…Zoospores of S. dermatodea were able to down regulate photosynthesis through dynamic photoinhibition while incomplete recovery in zoospores of L. saccharina results from the longer time required for de novo synthesis and replacement of damaged D1 protein in the thylakoid membrane. Future studies on D1 protein and zeaxanthin synthesis (Adams and Demming-Adams 1992;Andersson et al 1992;Bischof et al 2002) are necessary to confirm this hypothesis. Damage to reaction centers of PSII affecting the water-oxidizing complex (Turcsányi and Vass 2002) might be responsible for the lower and delayed photosynthetic recovery in UVR-exposed zoospores.…”

“…Cell culture dishes (35 mm · 10 mm Corning, Corning Inc., NY, USA) were covered with one of the following filters to cut off different wavelength ranges from the spectrum emitted by the fluorescent tubes: Ultraphan transparent (Digefra GmbH, Germany); Folanorm (Folex GmbH, Germany) or Ultraphan URUV farblos corresponding to the PAR+UV-A+UV-B (PAB), PAR+UV-A (PA), and PAR (P) treatments, respectively. The spectral properties of the foils used are published elsewhere (Bischof et al 2002). UVR was measured using a cosine sensor connected to a UV-VIS Spectrometer (Marcel Kruse, Bremerhaven, Germany) below the cut-off filters at 5.65 W m )2 UV-A and 0.47 W m )2 UV-B.…”