CELL SURVIVAL CHARACTERISTICS AND MOLECULAR RESPONSES OF ANTARCTIC PHYTOPLANKTON TO ULTRAVIOLET‐B RADIATION¹

Abstract

Twelve species of Antarctic diatoms were studied to assess UV sensitivity in relation to cellular and molecular aspects of DNA damage and repair. Responses of cell survival, induction of DNA damage, and DNA repair capacity were determined. There was a wide range of interspecific UV‐sensitivity among diatoms. D37 values (average fluence to kill one cell) ranged from 681 J · m−2 (most sensitive) to 25,338 J · m−2 (most resistant). Molecular analysis (by radioimmunoassay) of UV‐induced DNA damage [induction of cys‐syn cyclobutane dimers and pyrimidine (6‐4) pyrimidone photoproducts] also revealed considerable variability among species [0.98–84 lesions · (108 daltons DNA)−1 induced by exposure to 2500 J · m−2]. Repair of DNA damage ranged from 0.18 to 2.72 lesions removed · (108 daltons DNA)−1 in 6 h; removal represented 0.72–73.5% of initial damage. Comparison of cellular responses associated with photoenhanced repair and nucleotide excision (“dark”) repair indicated that light‐mediated correction of UV damage was an important factor in cell survival. There was a relationship between the number of photoproducts induced and cell survival, but not between repair efficiency and survival. The data also indicate a general dependence of photoproduct induction and D37 values on cell size and shape (expressed as the surface area: volume ratio which ranged from 0.07 to 0.66 between species) and suggest that these factors are indicators of UV sensitivity. Smaller cells with greater surface area: volume ratios sustained more damage per unit of DNA, had lower D37 values, and were more sensitive to UV exposure. The wide species variations observed in molecular and cellular responses to UV exposure emphasize the ecological implications of changes in natural UV regimes. These changes can act as determinants of cell size and taxonomic structure within phytoplankton communities and have as yet unknown effects on trophic interactions within the Antarctic ecosystem.

Effect of solar ultraviolet radiation on bacterio- and phytoplankton activity in a large coral reef lagoon (southwest New Caledonia)

“…However, the relationship between size and sensitivity is not straightforward. For example, Karentz et al (1991), studying 12 species of diatoms, concluded that smaller cells sustained greater amounts of damage per unit of DNA. On the other hand, Helbling et al (2001) showed that small flagellates are strongly inhibited by UV-R, but are able to acquire resistance to UV-R by photoadaptive processes.…”

Ultraviolet radiation sensitivity of photosynthesis in phytoplankton from an estuarine environment

“…Carotenoids also act in a photoprotective function against high irradiance (Demers et al 1991). Organisms have varying abilities to reverse the effects of UV radiation (Karentz et al 1991;Lesser et al 1996). Repair may be ongoing , may mostly occur after UV exposure (A. T. Banaszak et al unpubl.…”

Models for ultraviolet radiation—dependent photoinhibition of Lake Erie phytoplankton

“…It has not been easy to develop fully satisfactory estimates of the effects of UVR on primary production, partly because UVR belongs to a continuous solar radiation spectrum that acts both beneficially and detrimentally on photosynthesizing organisms. Solar radiation drives the photosynthetic conversion of inorganic carbon to organic substrates, yet excessive visible light, as well as UVR, can inhibit photosynthesis (Cullen and Lesser 1991;Villafañe et al 1995), damage intracellular components such as DNA (Karentz et al 1991;Prézelin et al 1994), and inactivate certain key photosynthetic proteins (Greenberg et al 1989;Wilson et al 1995). Another major complication in assessing the effects of UVR on plankton is the natural variability in exposure regime that is associated with vertical mixing processes (Smith and Cullen 1995).…”

“…Phytoplankton have evolved a variety of mechanisms to prevent or counteract the damage from UVR and excessive 1 Corresponding author (vphiriar@sciborg.uwaterloo.ca). light, such as DNA photoreactivation, the synthesis of photoprotective pigments, and dark repair processes (Karentz 1999;Roy 2000). Although the timescales of photoinhibition vary on the order of minutes to hours, some photoprotection measures occur within seconds or minutes (e.g., energy dissipation via fluorescence, state transitions, or nonradiative decay), and others occur on the order of hours to days (e.g., synthesis of protective pigments, or chemical quenchers; Ferris and Christian 1991;Villafañe et al 1995).…”