COMBINED EFFECTS OF ULTRAVIOLET RADIATION AND TEMPERATURE ON MORPHOLOGY, PHOTOSYNTHESIS, AND DNA OF ARTHROSPIRA (SPIRULINA) PLATENSIS (CYANOPHYTA)¹

Abstract

Natural levels of solar UVR were shown to break and alter the spiral structure of Arthrospira (Spirulina) platensis (Nordst.) Gomont during winter. However, this phenomenon was not observed during summer at temperatures of ∼30°C. Since little has been documented on the interactive effects of solar UV radiation (UVR; 280-400 nm) and temperature on cyanobacteria, the morphology, photosynthesis, and DNA damage of A. platensis were examined using two radiation treatments (PAR [400-700 nm] and PAB [PAR + UV-A + UV-B: 280-700]), three temperatures (15, 22, and 30°C), and three biomass concentrations (100, 160, and 240 mg dwt [dry weight] · L(-1) ). UVR caused a breakage of the spiral structure at 15°C and 22°C, but not at 30°C. High PAR levels also induced a significant breakage at 15°C and 22°C, but only at low biomass densities, and to lesser extent when compared with the PAB treatment. A. platensis was able to alter its spiral structure by increasing helix tightness at the highest temperature tested. The photochemical efficiency was depressed to undetectable levels at 15°C but was relatively high at 30°C even under the treatment with UVR in 8 h. At 30°C, UVR led to 93%-97% less DNA damage when compared with 15°C after 8 h of exposure. UV-absorbing compounds were determined as negligible at all light and temperature combinations. The possible mechanisms for the temperature-dependent effects of UVR on this organism are discussed in this paper.

Ocean acidification mediates photosynthetic response to UV radiation and temperature increase in the diatom <i>Phaeodactylum tricornutum</i>

“…On the other hand, high levels of UV can lead to degradation of periplasmic carbonic anhydrase (CAe) (Wu and Gao, 2009), as well as Rubisco and D1 protein (Bischof et al, 2002;Bouchard et al, 2005), and increased temperature could have stimulated the repair of the damaged molecules. The beneficial effects of increased temperature on photosynthesis under UV stress have been previously documented (Sobrino and Neale, 2007;Gao et al, 2008;Halac et al, 2010;Helbling et al, 2011), showing lower UV-induced inhibition or damages at higher temperatures. Differential sensitivities to UV have been reported in marine picoplankters when grown under elevated CO 2 concentrations, with Nannochloropsis gaditana having lower sensitivity while Nannochloris atomus showed neutral response (Sobrino et al, 2005).…”

“…6a, c and e), reflecting a synergistic effect of pCO 2 rise and warming. This might be associated with enhanced activity of cellular enzymes and membrane fluidity, as they are temperature-dependent (Allakhverdiev et al, 2008), and accelerated molecular repair rates that usually increase with temperature within a species' thermal window (Conkling and Drake, 1984;Gao et al, 2008). In the presence of UV-B, NPQ in the LC-grown cells was lower than HC-grown ones, especially under the lower temperature treatment (Fig.…”

“…UVR (UV-A + UV-B) is known to inhibit growth and photosynthesis (Helbling et al, 1992;Heraud and Beardall, 2000;Gao et al, 2007a;Jiang and Qiu, 2011) and damage proteins and the DNA molecule (Grzymski et al, 2001;Xiong, 2001;Gao et al, 2008). However, moderate UVR levels were shown to increase photosynthetic carbon fixation (Nilawati et al, 1997;Barbieri et al, 2002), with UV-A (320-400 nm) even driving photosynthetic carbon fixation in the absence of PAR (Gao et al, 2007b).…”

Vertical Patterns of Early Summer Chlorophyll a Concentration in the Indian Ocean with Special Reference to the Variation of Deep Chlorophyll Maximum

“…In surface oceans, a series of environmental factors are known to control the biomass and distribution of phytoplankton. Light intensity influences phytoplankton growth and productivity through driving or photoinhibiting photosynthesis [3,4], while vertical mixing affects carbon fixation ability by balancing the damage and repair at high or low light levels [5,6]. The available trace metals (e.g., copper and iron) also lead to variations in phytoplankton biomass or size communities [7][8][9].…”

Enhanced Resistance to UV-B Radiation in Anabaena sp. PCC 7120 (Cyanophyceae) by Repeated Exposure

“…Cyanobacteria are a group of most primitive, plant-type photosynthetic organisms which contribute markedly to global CO 2 and N 2 fixation [18,42]. Various biological changes such as morphological, physiological, and biochemical responses in microalgae including cyanobacteria to UVBR have been reported [21,26,56]. The impacts of UVR on the growth, photosynthetic performance, morphology, and heterocyst formation of Anabaena sp.…”