Contributions of Visible and Ultraviolet Parts of Sunlight to Photoinhibition

Abstract

Photoinhibition is light-induced inactivation of PSII, and action spectrum measurements have shown that UV light causes photoinhibition much more efficiently than visible light. In the present study, we quantified the contribution of the UV part of sunlight in photoinhibition of PSII in leaves. Greenhouse-grown pumpkin leaves were pretreated with lincomycin to block the repair of photoinhibited PSII, and exposed to sunlight behind a UV-permeable or UV-blocking filter. Oxygen evolution and Chl fluorescence measurements showed that photoinhibition proceeds 35% more slowly under the UV-blocking than under the UV-permeable filter. Experiments with a filter that blocks UV-B but transmits UV-A and visible light revealed that UV-A light is almost fully responsible for the UV effect. The difference between leaves illuminated through a UV-blocking and UV-transparent filter disappeared when leaves of field-grown pumpkin plants were used. Thylakoids isolated from field-grown and greenhouse-grown plants were equally sensitive to UV light, and measurements of UV-induced fluorescence from leaves indicated that the protection of the field-grown plants was caused by substances that block the passage of UV light to the chloroplasts. Thus, the UV part of sunlight, especially the UV-A part, is potentially highly important in photoinhibition of PSII but the UV-screening compounds of plant leaves may offer almost complete protection against UV-induced photoinhibition.

UV-B Perception and Acclimation in Chlamydomonas reinhardtii

“…We first established that under our conditions broadband UV-B stress indeed impacted photosynthetic efficiency by decreasing the maximum quantum yield of PSII as determined by chlorophyll fluorescence spectroscopy (Fv/Fm) ( Figure 4B, "Non-acclimated"). Decreased photosynthetic efficiency due to light-induced damage is generally referred to as photoinhibition (Hakala-Yatkin et al, 2010). The extent of UV-B-induced photoinhibition increased with broadband UV-B treatment time ( Figure 4B).…”

Ultraviolet and photosynthetically active radiation can both induce photoprotective capacity allowing barley to overcome high radiation stress

“…Wargent et al, 2009;Gruber et al, 2010) and carbon assimilation (e.g. Guidi et al, 2011;Klem et al, 2012;Urban et al, 2006) due to their ability to damage DNA and cause production of reactive oxygen species (Hakala-Yatkin et al, 2010;Hideg et al, 2013). However, susceptibility to UV-B radiation is dependent on the complex interplay between protection, repair and damage, and as a consequence, plant responses vary depending on dose, UV-spectral composition, acclimation time, genotype and other co-occurring environmental factors (Jordan, 2002;Kataria et al, 2014).…”

“…High PAR can cause photoinhibition, a decrease in the photochemical performance of PS II. It has been reported that photodamage to PS II under sunlight is primarily associated with UV rather than PAR (Hakala-Yatkin et al, 2010;Takahashi et al, 2010). Plants have evolved a range of mechanisms to decrease damaging effects of either UV or PAR absorbed by leaves.…”

Reactive oxygen species: Reactions and detection from photosynthetic tissues

“…In plant leaves, scopoletin mainly localizes to the cell wall but also penetrates to the cells [184]. The usability of scopoletin in plants in vivo is limited by the need to use ultraviolet (UV) wavelengths (346 nm) for excitation, as plant leaves strongly absorb UV light [201]. The 435 nm emission of scopoletin is also strongly absorbed by Chl a. Scopoletin has been used for measurement of H 2 O 2 in root cells [202] and in the incubation media of callus cells [203] but also from leaves of Pseudowintera colorata [204].…”