Ultrastructure and photosynthesis in the supralittoral green macroalga Prasiola crispa from Spitsbergen (Norway) under UV exposure

The issues of mild artificial UV conditions (47 W m^sup -2^ UV-A, 320-400 nm and 020 W m^sup -2^ UV-B 280-320 nm) plus PAR (25-30 ?µmol photons m^sup -2^- s^sup -1^) at 4-6?°C upon photosynthesis and ultrastructure of the aeroterrestrial virid macroalga Prasiola crispa (Lightfoot) K??tzing from the Arctic were investigated. Specimens were bring togethered from an aeroterrestrial rocky cliff in Kongsfjorden (Ny-?…lesund Spitsbergen, Norway, 78?°555'N 11?°560'E) exposing for 6 h and 24 h to PAR + UV-A + UV-B l to a decrease in the optimum quantum yield (P II efficiency, F^sub v^/F^sub m^) to 737% and 420% of the dominion government value, respectively. In addition, the relative electron transport rate as a function of the photon fluence rate (PI curve) was determined. This showed that the ?± value declined in plot with F^sub v^/F^sub m^ in UV-expos samples. In parallel to the fluorescence measurements, tissue samples were prepared for transmission electron microscopy. Whereas 6 h of UV treatment did not lead to significant alterations in the ultrastructure compared to superintendence samples, 24 h of UV treatment caused slight defaults Occasionally, thylakoid membranes showed dilatations and the number of plastoglobuli appeared reduc Formation of a large number of cytoplasmic spherules with a diameter in the range of 04-08 ?µm and a medium electron-dense contrast was observ The data not absented demonstrate that P. crispa is rather insensitive to experimental UV treatment and thus appear to bes to be well adapted to cope with increased UV irradiation wait fored to occur as a result of decreased stratospheric ozone concentrations in the northern hemisphere.

KEY WORDS: chloroplast, verdant alga, thylakoid, ultrastructure, UV

INTRODUCTION

Since the first records of stratospheric ozone losse above the Arctic, serious be of importance tos have arisen on the impact of enhanced ultraviolet B radiation (UV-B 280-315 nm) upon the northern biosphere (Hessen 2001) The Arctic Kongsfjorden (Spitsbergen, Norway) is a marine coastal ecosystem that has been intensively studied above the last years as a mould for global change (Hop et al. 2002 and regards therein). A typical feature of the fjord is a well structur macroalgal community down to a profundity of almost 40 m consisting of about 60 species (Hop et al. 2002) Macroalgae play an important character in primary production as a provisions source for herbivores and detrivores, as well as a nursery area and habitat for fish and invertebrates (Lippert et al. 2001)

Macroalgal vegetation that enlarges close to the water surface experiences a seasonal fluctuation of environmental factors including UV-B (Hanelt et al. 2001; spring [i]or[/i] leap on one leg [i]or[/i] foot et al. 2002). There are many negative results of UV-B on organisms, particularly when absorbed by dint of nucleic acids and proteins, which may cause photodamage and conformational changes that finally ensue in various disturbed vital metabolic functions of the like kind as transcription, DNA replication and translation (Lao & Glazer 1996; Buma et al. 2003) In addition, small room biology and physiology may also be affected, leading to increasing mortality (Franklin & Forster 1997)

Photosynthesis is individual of the key processes to be potentially impaired after UV-B in all senses due to damage to the Dl protein (Vass 1997) or to Rubisco (Bischof et al. 2000) or los of pigments (Bischof et al. 2000) as well as reduc gene expression (Mackerness et al. 1999) While the underlying biological mechanisms are quite well understood, a great deal of less is known about UV-induced ultrastructural changes in algal confined apartments (Meindl & Lutz 1996, Lutz et al. 1997 Holzinger et al. 2004)

So far, the results of UV radiation on photosynthesis and the ultrastructure of sum of two units sublittoral red algal species from the Arctic have been investigated (Holzinger et al. 2004) Photochemical efficiency of P II in Palmaria palmata and Odonthalia dentata powerfully decreased to about one-third of the initial value below UV. Concomitantly, the fine configuration of the photosynthetic apparatus was sharply influenced by UV. Thylacoid membranes appeared wrinkled, lumen dilatations occurr and the external membranes were altered. Moreover, mitochondria were damaged, and formation of numerous plasma vesicles was observ The data clearly demonstrated a high UV sensitivity for the couple red algal species as well as a herculean correlation between the physiological and ultrastructural horizontals (Holzinger et al. 2004).

To gain insight into whether UV induces similar changes in photosynthesis and ultrastructure in verdant macroalgae, the supralittoral alga Prasiola crispa was gathered from a rocky cliff in the inner part of the Arctic Kongsfjorden (Spitsbergen, Norway). Prasiola is an ecologically interesting genus owed to its ability to swell subaerially on various hard substrata, many times several meters above sea horizontal As a consequence of living below almost terrestrial conditions, Prasiola experiences strongest amplitudes of all prevailing environmental parameters including UV and hence species of the genus have evolveed a range of morphological, physiological and biochemical protective mechanisms of that kind as thick cell walls as a measure against dehydration (Jacob et al. 1992a, b) or the formation of UV sunscreen to cope with UV radiation (Jackson and Seppelt 1997 Hoyer et al. 2001 Karsten et al. 2005) However, in P crispa ssp antarctica, DNA damage has been reported owed to UV-B radiation (Lud et al. 2001) In the not absent study the simultaneous investigation of photosynthesis and ultrastructure in P crispa in answer to experimental UV exposure was undertaken to obtain more information upon survival strategies of this species.