Hydrogen Peroxide Production by the Spot-Like Mode Action of Bisphenol A

Abstract

Bisphenol A (BPA), an intermediate chemical used for synthesizing polycarbonate plastics, has now become a wide spread organic pollutant. It percolates from a variety of sources, and plants are among the first organisms to encounter, absorb, and metabolize it, while its toxic effects are not yet fully known. Therefore, we experimentally studied the effects of aqueous BPA solutions (50 and 100 mg L −1 , for 6, 12, and 24 h) on photosystem II (PSII) functionality and evaluated the role of reactive oxygen species (ROS) on detached leaves of the model plant Arabidopsis thaliana. Chlorophyll fluorescence imaging analysis revealed a spatiotemporal heterogeneity in the quantum yields of light energy partitioning at PSII in Arabidopsis leaves exposed to BPA. Under low light PSII function was negatively influenced only at the spot-affected BPA zone in a dose-and timedependent manner, while at the whole leaf only the maximum photochemical efficiency (Fv/Fm) was negatively affected. However, under high light all PSII photosynthetic parameters measured were negatively affected by BPA application, in a timedependent manner. The affected leaf areas by the spot-like mode of BPA action showed reduced chlorophyll autofluorescence and increased accumulation of hydrogen peroxide (H 2 O 2). When H 2 O 2 was scavenged via N-acetylcysteine under BPA exposure, PSII functionality was suspended, while H 2 O 2 scavenging under non-stress had more detrimental effects on PSII function than BPA alone. It can be concluded that the necrotic death-like spots under BPA exposure could be due to ROS accumulation, but also H 2 O 2 generation seems to play a role in the leaf response against BPA-related stress conditions.

Rapid Hormetic Responses of Photosystem II Photochemistry of Clary Sage to Cadmium Exposure

“…Thus, since ROS are formed by energy transfer ( 1 O 2 ) and electron transport (H 2 O 2 ) simultaneously, it appears likely that their action interferes with the signaling pathways sometimes to antagonize each other. It has been frequently shown that hydrogen peroxide disperses through leaf veins to act as a long-distance molecule, triggering the stress defence response in plants [20,25,27,83,89].…”

“…A basal level of ROS is needed for optimal growth (control) [20,25], with a low increased level of ROS to be beneficial for triggering defense responses (5 days Cd exposure), and a high level of ROS (8 days Cd exposure) to be out of the boundaries and harmful to plants [20,34]. Photosystem II responses to short time Cd exposure of S. sclarea can be described as a hormetic response (Figure 14), representing an "over-compensation" response to a disruption in homeostasis [42].…”

“…Nevertheless, other studies have shown a dose dependent negative impact of Cd that increases with the generation of ROS and oxidative damage and the inhibition of photosynthetic rate to follow [5,[100][101][102][103][104][105][106]. On the other hand, protection to stress through ROS production [25,107] has been shown that it can be regulated by NPQ in such a way so that plants can cope with stress [22,26,27].…”

Hormetic Responses of Photosystem II in Tomato to Botrytis cinerea

“…ROS, such as superoxide anion radical (O 2 • − ), hydrogen peroxide (H 2 O 2 ), and singlet oxygen ( 1 O 2 ), produced in chloroplasts play dual roles as they generate oxidative stress and also confer essential biological function as redox signaling in response to biotic and abiotic stress conditions [ 14 , 15 , 16 ]. The role of chloroplast antioxidants, that often have overlying or interrelating functions, is not to totally eliminate ROS, but rather to achieve a suitable balance between production and removal so that to counterpart photosynthetic function, permitting an effective diffusion of signals to the nucleus and adjusting a plethora of physiological functions [ 13 , 16 , 17 ]. Leaf image analysis is also used as an objective and accurate alternative method to quantify ROS production at the affected leaf areas, and has proven to be a useful tool in plant science [ 15 ].…”

“…A low-level of stress or a short exposure duration has been frequently referred to stimulate plant performance [ 13 , 20 , 40 , 41 , 42 , 43 , 44 ]. This enhancement can be achieved through a basal level of ROS [ 9 , 10 , 13 , 16 , 45 ], that is being regulated by the photoprotective mechanism of photosynthesis, the non-photochemical quenching (NPQ) [ 23 , 43 , 46 ]. NPQ under stress conditions decreases electron transport rate (ETR) to avoid ROS formation [ 35 , 47 ].…”