UV-B effects on leaves—Oxidative stress and acclimation in controlled environments

Abstract

As the steady decline in the Earth's stratospheric ozone layer and parallel increase in solar ultraviolet-B (UV-B: 280-315 nm) has come to an end, the focus of plant UV research has been shifted from regarding UV-B as threatening plant life to recognizing it as a regulatory factor. While UV-B photoreceptor mediated signaling is increasingly understood, the role of UV-B inducible reactive oxygen species is still to be explored. Earlier experiments with high UV-B irradiation doses and isolated thylakoid membranes demonstrated the potential of UV-B to trigger oxidative stress.However, under realistic UV conditions pro-oxidants cannot be reliably traced in more complex biological samples possessing an array of antioxidant defenses. In the absence of direct experimental evidence we must rely on indications and propose hypotheses on how and whether pro-oxidants, such as reactive oxygen species contribute to acclimative responses. Here we briefly review how a balance between pro-oxidants and antioxidants is affected by UV-B in whole plant experiments performed in controlled environments. A working hypothesis is proposed in which the extents of UVinduced peroxidase and superoxide dismutase activations affect the success of acclimation to UV-B.

UVA + B treatment affects antioxidant system and phytochemicals of parsley plant under different concentrations of Zn

“…The activities of antioxidant enzymes POD and CAT in UV treated plants increased in this study. The enhancement in the activities of these enzymes in response to UV-B treatment were reported by several authors ) Nasibi and Kalantari, 2005;Czégény et al, 2016(. Antioxidant enzymes play a significant role in the dynamic equilibration between free oxygen radicals production and destruction.…”

“…Antioxidant enzymes play a significant role in the dynamic equilibration between free oxygen radicals production and destruction. The responses of antioxidant enzymes to UV radiation vary among plants species ) Tossi et al, 2009;Salama et al, 2011;Czégény et al, 2016(. The increasing in the activities of antioxidant enzymes could be the indicator of build-up of a protective mechanism to reduce oxidative damages induced by stress (Harinasut et al, 2003;Chawla et al, 2013).…”

“…Plants have obligate requirement for sun light are more susceptible to this radiance. UV radiation increases the production of reactive oxygen species (ROS) that are extremely cytotoxic ) Mahdavian et al, 2008;Czégény et al, 2016(. The antioxidant system is one of the most important mechanisms responsible for detoxifying the free radicals.…”

Solar UV Upregulates Photoprotection but Slows Photosynthesis in Subalpine Australian Plants

“…Herbaceous species generally show weaker screening capacity than other life forms (Day et al, 1992). A likely consequence is that significant amounts of UV reach the underlying mesophyll, stimulating generation of reactive oxygen species (ROS) (Czégény et al, 2016) and potentially damaging cellular organelles involved with photosynthesis (Ivanova et al, 2008). Fittingly, G. antrorsum maintained the greatest concentrations of glutathione (Noctor et al, 2012) and synthesized ascorbate upon exposure to UV (Foyer et al, 1994;Gao and Zhang, 2008;Kataria et al, 2012).…”

“…UV that reaches the mesophyll can affect photosynthetic apparatus in similar fashion to excess radiation of longer wavelengths, in particular via accumulation of reactive oxygen species (ROS) in the thylakoid membrane (Foyer et al, 1994) and/or by inhibiting repair of PSII (Nishiyama et al, 2006). At the cellular level, UV wavelengths can exacerbate oxidative stress (Barta et al, 2004;Snyrychova et al, 2007) via the formation of oxygen radicals from peroxidases and oxidases, chlorophyll molecules and metabolic reactions in peroxisomes, as well as in the electron transport chain (for reviews see Kataria et al, 2014;and Czégény et al, 2016). UV radiation also promotes the production of hydrogen peroxide (H 2 O 2 ), the stable form of oxidized oxygen, and its subsequent photosensitive breakdown to highly oxidizing hydroxyl radical (Czégény et al, 2014).…”