UV effects on photosynthesis and DNA in propagules of three Antarctic seaweeds (Adenocystis utricularis, Monostroma hariotii and Porphyra endiviifolium)

Abstract

Ozone depletion is highest during spring and summer in Antarctica, coinciding with the seasonal reproduction of most macroalgae. Propagules are the life-stage of an alga most susceptible to environmental perturbations therefore, reproductive cells of three intertidal macroalgal species Adenocystis utricularis (Bory) Skottsberg, Monostroma hariotii Gain, and Porphyra endiviifolium (A and E Gepp) Chamberlain were exposed to photosynthetically active radiation (PAR), PAR + UV-A and PAR + UV-A + UV-B radiation in the laboratory. During 1, 2, 4, and 8 h of exposure and after 48 h of recovery, photosynthetic eYciency, and DNA damage were determined. Saturation irradiance of freshly released propagules varied between 33 and 83 mol photons m ¡2 s ¡1 with lowest values in P. endiviifolium and highest values in M. hariotii. Exposure to 22 mol photons m ¡2 s ¡1 PAR signiWcantly reduced photosynthetic eYciency in P. endiviifolium and M. hariotii, but not in A. utricularis. UV radiation (UVR) further decreased the photosynthetic eYciency in all species but all propagules recovered completely after 48 h. DNA damage was minimal or not existing. Repeated exposure of A. utricularis spores to 4 h of UVR daily did not show any acclimation of photosynthesis to UVR but fully recovered after 20 h. UVR eVects on photosynthesis are shown to be species-speciWc. Among the tested species, A. utricularis propagules were the most light adapted. Propagules obviously possess good repair and protective mechanisms. Our study indicates that the applied UV dose has no long-lasting negative eVects on the propagules, a precondition for the ecological success of macroalgal species in the intertidal.

Stress tolerance of Antarctic macroalgae in the early life stages

“…Notwithstanding such species-specific differences, photosynthetic characteristics of reproductive cells allowed us to distinguish between eulittoral and sublittoral algae, the former having higher irradiance saturation. These results are in agreement with the actual position of these species on the shore, and they confirm previous reports of [4].…”

“…It must be emphasized that differences in UV tolerance between propagules of different species are a reflection of both the capacity for stress tolerance, as well as other morphofunctional aspects related to cell size, pigmentation, previous UV exposure history within gametangia/sporangia [12], and even the levels and time of UV exposure used in experiments (see Table 1). In the case of size, UV susceptibility has been shown to decrease with increasing cell size in terms of F v /F m [6] and DNA damage [4,6]. In larger propagules observed in our study, such as carpospores of Iridaea (18 ± 2 μm) and Pyropia (12 ± 1 μm) and gamentangia of Ascoseira (22 ± 4 μm), direct UV effect was lower, most likely resulting from the longer pathway for UV penetration [8].…”

“…However, during the last decade, photosynthetic characteristics and UV effects on microscopic developmental stages, e.g., spores, gametes, propagules and plantlets, of some selected Antarctic macroalgae have been published [4−6] (see Table 1). These studies report that early life stages are also extremely shade-adapted and susceptible to environmental stresses, such as exposure to UV radiation [4,7]. Even though the effect of UV on microscopic life history Results of the present study are marked in bold, and the differences among photosynthetic parameters of the studied species are denoted by different letters (Tukey test; P < 0.05).…”

“…In contrast, [4] reported that spores of P. endiviifolia are strongly shade-adapted and that propagules of A. utricularis and M. hariotii seem to be less shade-adapted (for comparison, see Table 1). Differences between these studies could result from the number of spores used in the measurements, time of release of spores or reproductive season.…”

Susceptibility of spores of different ploidy levels from AntarcticGigartina skottsbergii(Gigartinales, Rhodophyta) to ultraviolet radiation

“…(Roleda et al 2005(Roleda et al , 2006b, and gametes of Ascoseira mirabilis (3 mm; Roleda et al 2007b), possibly contributed to lower DNA damage due to the longer pathlength for UVR to reach the nucleus in larger cells (Garcia-Pichel 1994). Propagules of three Antarctic macroalgae, Adenocystis utricularis, Monostroma hariotii, and Porphyra endiviifolium, inhabiting the upper eulittoral zone, also exhibited an inverse correlation between increasing cell size and amount of DNA damage (Zacher et al 2007). Aside from the functional significance of spore size, the hypothesis that diploid microscopic stages may be more resistant to the deleterious effects of UVR was also previously raised by Altamirano et al (2003) when comparing the sensitivity of zygotes of Fucus species (.…”