UVB Effects on the Photosystem II‐D1 Protein of Phytoplankton and Natural Phytoplankton Communities

Abstract

The reaction center of photosystem II is susceptible to photodamage. In particular the D1 protein located in the photosystem II core has a rapid, light-dependent turnover termed the photosystem II repair cycle that, under illumination, degrades and resynthesizes D1 protein to limit accumulation of photodamaged photosystem II. Most studies concerning the effects of UVB (280-320 nm) on this cycle have been on cyanobacteria or specific phytoplankton species rather than on natural communities of phytoplankton. During a 5-year multidisciplinary project on the effects of UV radiation (200-400 nm) on natural systems, the effects of UVB on the D1 protein of natural phytoplankton communities were assessed. This review provides an overview of photoinhibitory effects of light on cultured and natural phytoplankton, with an emphasis on the interrelation of UVB exposure, D1 protein degradation and the repair of photosystem II through D1 resynthesis. Although the UVB component of the solar spectrum contributes to the primary photoinactivation of photosystem II, we conclude that, in natural communities, inhibition of the rate of the photosystem II repair cycle is a more important influence of UVB on primary productivity. Indeed, exposing tropical and temperate phytoplankton communities to supplemented UVB had more inhibitory effect on D1 synthesis than on the D1 degradation process itself. However, the rate of net D1 damage was faster for the tropical communities, likely because of the effects of high ambient light and water temperature on mechanisms of protein degradation and synthesis.

Temperature-dependent growth and photophysiology of prokaryotic and eukaryotic oceanic picophytoplankton

“…This has also been found in larger phytoplankton species, such as the diatoms Chaetoceros gracilis, Thalassiosira pseudonana, and T. weissflogii (So b rino & Neale 2007, Halac et al 2010, Helbling et al 2011. Reduced levels of photoinhibition may be associated with enhanced enzymatic conversions of the xanthophyll pigment cycle (Demmig-Adams & Adams 1992), enhanced D1 repair (Bouchard et al 2006) and the potential enhancement of Rubisco activity (Helbling et al 2011). Further study is neccessary to confirm whether these processes are also involved in temperature acclimation in P. marinus, Prochlorococcus sp., Ostreococcus sp.…”

Combined effects of increased UV-B and temperature on the pigment-determined marine phytoplankton community of the St. Lawrence Estuary

“…Here we tested the hypothesis that algal biomass, community composition and photosynthetic performance would benefit from simultaneous increases in UV-B and temperature and examined the role of photo protective xanthophyll cycles (XC) in the phytoplankton response (Buma et al 2000, Sobrino et al 2005). In addition, we contrasted the phytoplankton response during all 8 d of the ex periment with that during the nutrientlimited post-bloom period to see if nutrient-stressed cells show greater sensitivity towards UV-B stress, as observed in a number of previous studies (Bouchard et al 2006, Longhi et al 2006, Beardall et al 2009, Korbee et al 2010.…”

In situ dynamics of O2, pH and cyanobacterial transcripts associated with CCM, photosynthesis and detoxification of ROS

“…Levels of ROS may also increase as a consequence of both ultraviolet irradiation and excess excitation of the photosynthetic apparatus by high levels of photosynthetically active radiation (400-700 nm). ROS can severely damage cellular components, including the photosynthetic apparatus itself (Aro et al, 2005;Bouchard et al, 2006). Photoinhibition, a consequence of photodamage to photosystem II, can lead to a further rise of ROS levels.…”