Acclimation of phytoplankton to UV-B radiation:oxidative stress and photoinhibition of photosynthesis are not prevented by UV-absorbing compounds in the dinoflagellate Prorocentrum micans

Abstract

Experiments on the temperate marine dinoflagellate Prorocentrum mjcans showed that cultures acclimated to moderate intensities (120 pm01 quanta m-2 S-') of visible radiation and supplemental ultraviolet (UV) ra&ation exhibited significant lnhibltlon of photosynthesis. This inhibltlon of photosynthesis caused a significant 30% decrease in s p e c~f~c growth rates for those cells exposed to UV radiation by the end of the 21 d culture. The mechanism for t h~s decrease in chlorophyll specific photosynthetic rate does not appear to have been damage to photosystem 11, as suggested for many acute exposure expenments Rather, significant decreases in chlorophyll per cell and the specific act~vities of the carboxylating enzyme, Rublsco, explain the observed decrease in photosynthesis. The decrease in cellular chlorophyll and Rubisco activities occurs despite the presence and accumulation of mycosporine-like amino acids, whose UV absorbing properties have been suggested as a n important protective mechanism against the deleterious effects of UV radiation. Our results also implicate oxidative stress, most likely a result of photodynamic interactions, a s the cause for the decrease in Rubisco activities. Action spectra generated from these experiments show a significant decrease in the wavelength-dependent effects of UV radiation in cultures exposed to UV radiation, suggesting that UVabsorbing compounds do provide some, if not complete, protection. Previous predictions about specific changes in the shape of action spectra were centered around the absorption maximum of individual UV-absorbing compounds. The observed changes in the overall shape of the UV action spectra for photosynthesis in P mlcans can be attributed to the broad overlapping absorption spectra of the suite of UV-absorbing compounds.

Analysis of limitations to CO2 assimilation on exposure of leaves of two Brassica napus cultivars to UV‐B

“…1992;He etal 1993;Huang e/a/. 1993;Kulandaivelu & Nedunchezhian 1993;He et al 1994a) and algae (Lesser 1996). Wilson et al (1995) have reported the appearance of a 66 kDa protein during UV-B exposure in oilseed rape, peas, tomato and tobacco, which they attributed to a photomodified form of the large subunit of Rubisco.…”

“…Consequently, PSII damage has often been implicated as the major potential limitation to photosynthesis in UV-B-treated leaves (Bomman 1989;Caldwell, Teramura & Tevini 1989;Stapleton 1992;Teramura & Sullivan 1994;Fiscus & Booker 1995), as is the case in the photoinhibition of photosynthesis by excess photosynthetically active radiation (380-700 nm) (Baker & Bowyer 1994), although it has been suggested that the mechanism of UV-B-induced damage may be different (Friso et al 1994;Jansen et al 1996). However, UV-B has been shown to inhibit photosynthesis, without an appreciable effect on PSII photochemistry, in pea (Nogues & Baker 1995), rice (Ziska & Teramura 1992), soybean (Middleton & Teramura 1993) and algae (Lesser 1996). Consequently, it would appear that UV-B inhibition of PSII photochemistry is not a ubiquitous primary limitation to photosynthesis.…”

Ultraviolet radiation shapes seaweed communities

“…This effect may be explained either by the activation of the antioxidative response, increased activity of repair and recovery mechanisms counteracting the inhibitory effects (see above), or by the formation of UV-screening compounds (Lesser 1996).…”

Methods and Models of Marine Optics Sources and Sinks

“…Vernet et al (1989) and Vernet and Whitehead (1996) suggest that UV-absorbing compounds in the bloom-forming dinoflagellates Lingulodinium polyedrum and Prorocentrum micans have a photoprotective effect. In contrast, Lesser (1996), did not find that UV-absorbing compounds prevented UV-induced photodamage in P. micans. However, Lesser's study consisted of a 21 day incubation in which samples were only taken at the end points.…”