Journal Article

Contrasting Effects of UV-A and UV-B on Photosynthesis and Photoprotection of β-carotene in two <i>Dunaliella</i> spp.

Andrea L. White and Leland S. Jahnke

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 43, issue 8, pages 877-884
Published in print August 2002 | ISSN: 0032-0781
Published online August 2002 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcf105
Contrasting Effects of UV-A and UV-B on Photosynthesis and Photoprotection of β-carotene in two Dunaliella spp.

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Photosynthetic and antioxidant responses following exposure to either ultraviolet-A or ultraviolet-B were contrasted in two species of the unicellular green alga, Dunaliella. Species selection was based on the ability of Dunaliella bardawil (UTEX 2538) to accumulate inter-thylakoid β-carotene when subjected to environmental stress while Dunaliella salina (UTEX 200) lacks this ability. Cells were cultured in high and low levels of visible light (150 and 35 µmol photons m–2 s–1, respectively) and then either ultraviolet-A (320–400 nm) or ultraviolet-B (290–320 nm) was added to visible light for 24-h exposure. A potassium chromate solution was found to be an ideal screen for removal of ultraviolet-A and ultraviolet-C from ultraviolet-B radiation. There were no significant changes in photosynthetic or antioxidant parameters following exposure to ultraviolet-B. Ultraviolet-A exposure significantly decreased photosynthetic parameters (>70% decrease in Fv/Fm and the ratio of light-limited to light-saturated photosynthesis in low β-carotene cells) and resulted in 50% increases in ascorbate peroxidase activity and ascorbate concentrations. The results suggest exposure to ultraviolet-A (but not ultraviolet-B) directly affects photosynthesis, observed as a loss of photosystem II electron transport efficiency and increased radical formation. This research indicates that the accumulated β-carotene in D. bardawil prevents UV-related photosynthetic damage through blue-light/ultraviolet-A absorption (supported by trends observed for antioxidant enzyme responses).

Keywords: Keywords: Antioxidants — β-carotene — Dunaliella bardawil — Dunaliella salina — Ultraviolet-A — Ultraviolet-B.; Abbreviations: Fv/Fm, ratio of variable fluorescence to maximal fluorescence of Chl; HL, high light (growth at 150 µmol photons m–2 s–1); LL, low light (growth at 35 µmol photons m–2 s–1); PAR, photosynthetically active radiation (400–700 nm); P100 : P500, ratio of light-limited to light-saturated photosynthetic oxygen evolution; ROS, reactive oxygen species; UV-A, ultraviolet-A; UV-B, ultraviolet-B.

Journal Article.  6400 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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