Physiological, biochemical, and ultrastructural responses of the green macroalga Urospora penicilliformis from Arctic Spitsbergen to UV radiation

Abstract

Exposure of the filamentous turf green alga Urospora penicilliformis to ambient and artificial ultraviolet radiation (UVR) revealed a considerable resilient species. This explains the ability of this alga to thrive in the middleupper intertidal zones of the Arctic sea where it is periodically exposed to environmental extremes. A transient UVR effect on photosynthesis under photosynthetically active radiation (PAR) + UV-A and PAR + UV-A + UV-B was found, but dynamic recovery of photoinhibition was observed immediately after reduction of the photon fluence rate of PAR in the absence or presence of background UVR under laboratory and natural solar radiation, respectively. Chlorophylls, carotenoids, and xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) concentrations were not significantly different between freshly collected samples and filaments exposed to additional laboratory radiation treatment. The ultrastructure of the U. penicilliformis gametophytes showed that the cells are well adapted to UVR. No significant ultrastructural alterations were observed in filaments exposed to different spectral irradiance in the laboratory compared to in situ acclimated specimen. The antioxidant α-tocopherol was detected in minute quantity while the search for flavonoid-like compounds was negative. Other UV screening strategies or certain genetically fixed physiological protective mechanism could be operating in this species responsible for their occurrence in higher shoreline and ecological success. Further molecular and biochemical studies are needed to elucidate the stress resistance in this turf alga. There is an indication that the extremely thick cell wall of U. penicilliformis gametophytes covered with mucilage sheath and dense layer of mineral depositions may provide a shield against unfavorable environmental conditions in general and against UVR in particular.

The vegetative arctic freshwater green alga Zygnema is insensitive to experimental UV exposure

“…As recently reported, the ultrastructure of the green alga Urospora is similarly insensitive to experimental UVR (Roleda et al, 2009b). In Urospora, an evident increase in electron dense bodies in the cytoplasm was observed under UVR.…”

“…For example, Urospora filaments exposed to comparable irradiance was already photoinhibited after 1 h and DF=F 0 m continuously decrease up to the maximum 16 h UVR treatment (Roleda et al, 2009a,b). Zygnema seems to have a better photoprotective mechanism compared to an Arctic green macroalga Urospora inhabiting the upper eulittoral zone where its E k , rETR max and a were significantly affected under UVR (Roleda et al, 2009b ) measured in this study imply that the solar radiation-exposed Zygnema is sunadapted. Higher saturating irradiance was observed in snow algae Chlamydomonas nivalis (E k = 523-826 mmol photons m À2 s…”

“…; Roleda et al, 2009b). This can be attributed to the higher solar radiation encountered by eulittoral macroalgae during austral spring in Antarctica, with sampling sites at lower latitude ($628S).…”

Effects of UVB radiation on the agarophyte Gracilaria domingensis (Rhodophyta, Gracilariales): Changes in cell organization, growth and photosynthetic performance

“…crispa exposed to 24 h PAR+ UVA + UVB radiation, the chloroplasts showed mild changes in thylakoids, a decrease in plastoglobuli, and the appearance of numerous electron-dense cells . However, other studies did not show ultrastructural damage in green algae, such as Zygnema exposed to PAR + UVA + UVB during 24 h (Holzinger et al, 2009) and U. penicilliformis (Roleda et al, 2010). The green microalgae Micrasterias denticulada C. Agardh also showed disintegration of the grana and a loss of the net-like arrangement of the thylakoids under UV radiation (Meindl and Lütz, 1996;Lütz et al, 1997).…”

“…At the same time, however, other studies have not shown ultrastructural damage in such green algae as Zygnema C. Agardh when exposed to PAR + UVA + UVB during 24 h (Holzinger et al, 2009) or Urospora penicilliformis (Roth) J.E. Areschoug (Roleda et al, 2010).…”