The Solar Action Spectrum of Photosystem II Damage    

Abstract

The production of oxygen and the supply of energy for life on earth rely on the process of photosynthesis using sunlight. Paradoxically, sunlight damages the photosynthetic machinery, primarily photosystem II (PSII), leading to photoinhibition and loss of plant performance. However, there is uncertainty about which wavelengths are most damaging to PSII under sunlight. In this work we examined this in a simple experiment where Arabidopsis (Arabidopsis thaliana) leaves were exposed to different wavelengths of sunlight by dispersing the solar radiation across the surface of the leaf via a prism. To isolate only the process of photodamage, the repair of photodamaged PSII was inhibited by infiltration of chloramphenicol into the exposed leaves. The extent of photodamage was then measured as the decrease in the maximum quantum yield of PSII using an imaging pulse amplitude modulation fluorometer. Under the experimental light conditions, photodamage to PSII occurred most strongly in regions exposed to ultraviolet (UV) or yellow light. The extent of UV photodamage under incident sunlight would be greater than we observed when one corrects for the optical efficiency of our system. Our results suggest that photodamage to PSII under sunlight is primarily associated with UV rather than photosynthetically active light wavelengths.Plants absorb sunlight to power the productive photochemical reactions of photosynthesis. Absorption of sunlight may also lead to deleterious photochemistry that damages the photosynthetic machinery. The PSII protein complex is important in this regard as it seems to be most susceptible to photodamage that results in photoinhibition and ultimately suppresses photosynthetic CO 2 assimilation, growth, and productivity (Long et al., 1994;Takahashi and Murata, 2008). Although plants have photoprotection mechanisms (Niyogi, 1999) and can effectively repair photodamaged PSII through the PSII repair cycle (Aro et al., 1993), photoinhibition still occurs under stressful environmental conditions Murata et al., 2007;Takahashi and Murata, 2008).The onset of photoinhibition is strongly correlated with the absorption of excessive excitation energy for photosynthesis. Therefore, photodamage to PSII was most readily assumed to be attributed to the excess light absorbed by photosynthetic pigments (Melis, 1999). However, the extent of photodamage that is measured under conditions where the repair of photodamaged PSII is prevented by inhibiting chloroplast protein synthesis (i.e. lincomycin or chloramphenicol) is directly proportional to the intensity of light (Mattoo et al., 1984; Tyystjärvi and Aro, 1996;Nishiyama et al., 2001Nishiyama et al., , 2004Allakhverdiev and Murata, 2004;Chow et al., 2005). Furthermore, recent studies have demonstrated that interruption of the Calvin cycle (Hakala et al., 2005;Takahashi and Murata, 2005;Takahashi et al., 2007) and inhibition of electron transfer between Q A and Q B (Jegerschö ld et al., 1990;Kirilovsky et al., 1994;Allakhverdiev et al., 2005) have no effect on the rate of ...

UV-B photoreceptor-mediated protection of the photosynthetic machinery in Chlamydomonas reinhardtii

“…Exposure to high light then rapidly triggers the development of qE and the conversion of violaxanthin to zeaxanthin. The action spectrum of photodamage to the photosynthetic electron transfer chain peaks in UV-B, at wavelengths that are most detrimental to PSII and the manganese cluster involved in water oxidation (33,34). Thus, predominant expression of LHCSR1 and PSBS under UV-B vs. LHCSR3 under high light may indicate an evolutionary divergence of the signaling pathways, potentially coupled to differences in the activities of these proteins.…”

“…Photodamage is associated with the UV-B part of the sunlight spectrum (33,34). In both Arabidopsis and Chlamydomonas, some of the UV-B-induced genes encode chloroplast proteins, and UV-B acclimation allows maintenance of photosynthetic efficiency under elevated levels of UV-B (32,35).…”

UV-B Perception and Acclimation in Chlamydomonas reinhardtii

“…The UV-B-induced photoinhibition we observed following broadband UV-B stress is presumably due to UV-B-induced PSII damage that exceeds the rate of repair (Takahashi et al, 2010;Takahashi and Badger, 2011). PSII subunit D1 in particular is a well known photosynthetic target of UV-B damage (Jansen et al, 1996;Takahashi et al, 2010), and photoinhibition has long been associated with a decrease in D1 and, albeit to a lesser extent, D2 protein level (Schuster et al, 1988). In agreement, we observed decreases in D1 and D2 protein levels in UV-B-exposed Chlamydomonas that correlated well with the extent of UV-B-induced photoinhibition.…”

“…When chloroplast translation was blocked using CAM, greater UV-B-induced photoinhibition was observed in response to UV-B stress, and, interestingly, both UV-B-acclimated and nonacclimated cultures were affected to the same extent. The UV-B-induced photoinhibition we observed following broadband UV-B stress is presumably due to UV-B-induced PSII damage that exceeds the rate of repair (Takahashi et al, 2010;Takahashi and Badger, 2011). PSII subunit D1 in particular is a well known photosynthetic target of UV-B damage (Jansen et al, 1996;Takahashi et al, 2010), and photoinhibition has long been associated with a decrease in D1 and, albeit to a lesser extent, D2 protein level (Schuster et al, 1988).…”

“…The PSII protein complex, with D1 and D2 at its core, is susceptible to photodamage leading to photoinhibition, particularly by UV-B (Takahashi et al, 2010). Photoinhibition is closely linked to the turnover of D1 and, to a lesser extent, D2 during such photodamage (Schuster et al, 1988).…”