Effects of UV Radiation on Photosynthesis of Natural Populations of Phytoplankton

Modert, C. W.; Norris, Dean R.; Blatt, Joel H.; Petrilla, R. D.

doi:10.1007/978-1-4684-8133-4_49

Cited by 3 publications

(3 citation statements)

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“…In spite of UVBR being often referred to as harmful, and UVA radiation (UVAR; 320–400 nm) being referred to as beneficial because of its induction of photorepair mechanisms, any portion of UVR or even visible radiation may have either deleterious or beneficial effects on certain organisms, depending on the dose absorbed by the organism and its tolerance to it. UVR with wavelengths ≥320 nm is effective in providing energy to photosynthesis (1,4,5), but only below a threshold, above which UVR decreases photosyn‐thetic rates. Several cellular components and processes can be adversely affected by UVR, including photosynthetic rates, pigments, photosystem II (PSII), electron transport, adenosine‐5′‐triphosphate synthesis, nitrogen metabolism, protein structure and functioning, nucleic acids, cell growth and division, motility and metal complexes (1).…”

Section: Introductionmentioning

confidence: 99%

“…Several cellular components and processes can be adversely affected by UVR, including photosynthetic rates, pigments, photosystem II (PSII), electron transport, adenosine‐5′‐triphosphate synthesis, nitrogen metabolism, protein structure and functioning, nucleic acids, cell growth and division, motility and metal complexes (1). In phytoplankton, these deleterious effects can be counteracted by several photoprotection mechanisms: (1) distribution and movements of organelles to minimize the absorption cross‐sectional area (6,7), as well as movement of the organism away from the source of radiation (8); (2) synthesis of screening substances, which absorb UVR (9–13); (3) absorption by pigments that dissipate the energy as heat or fluorescence (14,15); (4) synthesis of antioxidant enzymes (16–18) or accessory pigments that act as antioxidants (19–23) to protect the cell from reactive oxygen species; and (5) dark‐ and light‐activated mechanisms to repair UVR‐induced damage to nucleic acids (24,25). Vertical mixing alters phytoplankton exposure to UVR and can enhance or decrease photoinhibition, depending on the depth of the mixing layer (26), the mixing rate (27) and the light attenuation properties of the local seawater (28).…”

Section: Introductionmentioning

confidence: 99%

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Ultraviolet B‐photoprotection Efficiency of Mesocosm‐enclosed Natural Phytoplankton Communities from Different Latitudes: Rimouski (Canada) and Ubatuba (Brazil)

Mohovic

Gianesella

Laurion

et al. 2006

Photochem & Photobiology

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Photoprotection against UV-B radiation (UVBR; 280-320 nm) was examined in natural phytoplankton communities from two coastal environments at different latitudes: temperate Rimouski (Canada) and tropical Ubatuba (Brazil). Mesocosm experiments were performed at these sites to examine the response of phytoplankton to increases in UVBR that corresponded to local depletions of 30% and 60% in atmospheric ozone levels (low and high UVBR treatments, respectively). A fluorescence method using a pulse amplitude modulation fluorometer (Xe-PAM, Walz, Germany) with selective UV filters was used to estimate photoprotection, and these results were compared with an index of mycosporine-like amino acid (MAA) concentrations determined using spectrophotometry of methanol extracts. The present study provided the first evidence, to our knowledge, of the suitability of this in vivo fluorescence method for the estimation of UV photoprotection efficiency in natural phytoplankton. No significant differences were found for most of the variables analyzed between the light treatments used at both sites, but differences were found between sites throughout the duration of the experiments. Vertical mixing, used to maintain cells in suspension, likely alleviated serious UVBR-induced damage during both experiments by reducing the length of time of exposure to the highest UVBR irradiances at the surface. In Rimouski, this was the main factor minimizing the effects of treatment, because optical properties of the coastal seawater rapidly attenuated UVBR throughout the water column of the ca 2 m deep mesocosms. In this location, synthesis of MAAs and photoprotective pigments likely contributed to the observed phototolerance of phytoplankton and, hence, to their growth; however, in a comparison of the UVBR treatments, these variables showed no differences. In Ubatuba, where nutrient concentrations were significantly lower than those in Rimouski, light attenuation was less than that in Rimouski and UVBR reached the bottom of the mesocosms. UVBR penetration and the forced vertical mixing of the cells, without the possibility of vertical migration below this photostress zone, resulted in photo-inhibition, because confinement in the mesocosms forced cells to remain constantly exposed to high levels of irradiance during the daytime. Hence, additional effects of UVBR were masked in this experiment, because cells were damaged too much and phytoplankton populations were rapidly declining. There was also an overall preservation of MAAs, in contrast with chlorophyll (Chl) degradation, in spite of the fact that this UV screening was not sufficient to counteract photo-inhibition, which suggests an important role for these molecules, either in the overall photoprotection strategy or in other physiological processes. Altogether, local water characteristics, namely attenuation, mixing, and nutrients concentration, can strongly modulate the photoprotection strategies used by natural phytoplankton populations in coastal environments.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ultraviolet B‐photoprotection Efficiency of Mesocosm‐enclosed Natural Phytoplankton Communities from Different Latitudes: Rimouski (Canada) and Ubatuba (Brazil)

Mohovic

Gianesella

Laurion

et al. 2006

Photochem & Photobiology

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“…It could be that the absence of UV-A under the P condition deprived the algae of quanta for photosynthesis in the UV-A region. There is evi dence that short wavelengths, especially UV-A, can be used as energy for photosynthesis in phytoplankton (Modert et al 1982) and macroalgae (Halldal 1964). Further studies using solar radiation and more accurate laboratory experiments (us ing low and high PAR background) are needed to demonstrate fully the role of PAR in a scenario of enhanced UV radiation.…”

Section: Discussionmentioning

confidence: 98%

Effects of UV radiation on photosynthesis and excretion of UV-absorbing compounds of Dasycladus vermicularis (Dasycladales, Chlorophyta) from southern Spain

et al. 1998

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1998. Effects of UY radiation on photosynthesis and excretion of UY-absorbing compounds of Dasycladus vermicularis (Oasycladales, Chlorophyta) from southern Spain. Phy cologia 37: 379-387.Photosynthesis measured by chlorophyll fluorescence and oxygen exchange, pigment composition, and excretion of UY absorbing compounds were tested in the green alga Dasycladus vermicularis (Scopoli) Krasser following exposure to a combination of ultraviolet radiation and photosynthetically active radiation (PAR) in the laboratory. A preliminary chro matographic analysis of a thallus extract resulted in three separated substances, one showing an absorption maximum at 332 nm and two at 348 nm (UY-A). In contrast, the compound or set of compounds excreted to the medium had a spectrophotometric absorption maximum at 387 nm, indicating degradation or chemical conversion of the in situ precursors. The total absorbances of these UY-absorbing compounds in seawater and in the thallus were higher when plants were exposed to PAR alone (P) or to PAR + ultraviolet A and B radiation (PAB). This suggests that accumulation and excretion of this substance respond either to UY-B radiation or to a low irradiance of PAR. Pulse amplitude modulated fluorescence (PAM) and oxygen evolution were also affected by exposure to PAB and P. After 72 h exposure to PAB and P, the optimal (FiFm) quantum yield of fluorescence decreased between 15 and 30% compared to initial control, whereas lower photo inhibition of fluorescence occurred under PAR + UY-A conditions. Complete loss of O 2 evolution was observed in thalli irradiated for 24 h with PAB, whereas no effects after UY-A exposure were observed. In general, following 24 h exposure to the different treatments, an increase in light requirements for compensation (1,) and saturation (Ik) of photosynthesis was seen. Calculations of biologically effective UY doses using known action spectra revealed that fluorescence is impaired by 25% at UY-B doses above 900 kJ m-2 •

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Ultraviolet Radiation and Its Effects on Organisms in Aquatic Environments

Holm‐Hansen

Lubin

Helbling

1993

Environmental UV Photobiology

128

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Effects of UV Radiation on Photosynthesis of Natural Populations of Phytoplankton

Cited by 3 publications

References 6 publications

Ultraviolet B‐photoprotection Efficiency of Mesocosm‐enclosed Natural Phytoplankton Communities from Different Latitudes: Rimouski (Canada) and Ubatuba (Brazil)

Ultraviolet B‐photoprotection Efficiency of Mesocosm‐enclosed Natural Phytoplankton Communities from Different Latitudes: Rimouski (Canada) and Ubatuba (Brazil)

Effects of UV radiation on photosynthesis and excretion of UV-absorbing compounds of Dasycladus vermicularis (Dasycladales, Chlorophyta) from southern Spain

Ultraviolet Radiation and Its Effects on Organisms in Aquatic Environments

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