Low temperature has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). In order to study the role of ascorbate under chilling stress, the response of an ascorbate-deficient Arabidopsis thaliana mutant vtc2-1 to low temperature (2°C) was investigated. After chilling stress, vtc2-1 mutants exhibited oxidative damage. An increase in the H2O2 generation and the production of thiobarbituric acid reactive substances (TBARS), and a decrease in chlorophyll content, the maximal photochemical efficiency of PSII (Fv/Fm) and oxidizable P700 were also noted. The ratio of ascorbate/dehydroascorbate and reduced glutathione/oxidzed glutathione in the vtc2-1 mutants were reduced, compared with the wild type (WT) plants. The activities of antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and soluble antioxidants were lower in the vtc2-1 mutants than those in WT plants. These results suggested that the ascorbate-deficient mutant vtc2-1 was more sensitive to chilling treatment than WT plants. The low temperature-induced oxidative stress was the major cause of the decrease of PSII and PSI function in the vtc2-1 mutants. Ascorbate plays a critical role of defense without which the rest of the ROS defense network is unable to react effectively., L. Y. Wang ... [et al.]., and Obsahuje bibliografii
Its high oxidant capacity and ability to generate reactive oxygen species cause ozone toxicity. We studied the effect of ambient ozone on chlorophyll (Chl) a fluorescence, antioxidant enzymes, ascorbate contents, and lipid peroxidation in potatoes grown in open-top chambers in the field. In plants grown in non-filtered air (NFA), the development of non-photochemical quenching brought about a decrease in photosystem 2 (PS2) photochemical efficiency. Also the ability of PS2 to reduce the primary acceptor QA was lower than in charcoal-filtered, ozone-free air (CFA). Changes in Chl fluorescence yield were associated with changes in the thylakoid membrane. Ozone altered chloroplast membrane properties, as indicated by an increase in membrane lipid peroxidation in FNA-leaves compared to CFA plants. The ascorbate pool and activities of antioxidant enzymes were used for an indication of the detoxification system state in NFA and CFA leaves, whereby ozone affects the ascorbate concentration and decreases the antioxidant enzymes activities. The capacity of both detoxifying systems together was not high enough to protect potato plants against ambient ozone concentrations which reduced the photosynthetic yield in this potato cultivar. and A. Calatayud, J. W. Alvarado, E. Barreno.
Liriodendron tulipifera was exposed to gradually elevated ozone concentrations of 100-300 μg kg-1 in the naturally irradiated environment chamber. During 15 d of exposure to O3, net photosynthetic rate (PN) decreased and there was large difference between the control (C) and treatment with ozone (OT), while there was no significant difference in water use efficiency. Total chlorophyll content as well as the value of fluorescence parameter Fv/Fm decreased, while antioxidant enzyme activities related to ascorbate-glutathione cycle increased after 15 d of OT. Unchanged contents of ascorbate and glutathione indirectly suggest that the species hastened the antioxidant's oxidization/reduction cycle using enzymes instead of expanding their pool against oxidative stress. and S. Z. Ryang ... [et al.].
The physiological and biochemical behaviour of rice (Oryza sativa, var. Jyoti) treated with copper (II) oxide nanoparticles (CuO NPs) was studied. Germination rate, root and shoot length, and biomass decreased, while uptake of Cu in the roots and shoots increased at high concentrations of CuO NPs. The accumulation of CuO NPs was observed in the cells, especially, in the chloroplasts, and was accompanied by a lower number of thylakoids per granum. Photosynthetic rate, transpiration rate, stomatal conductance, maximal quantum yield of PSII photochemistry, and photosynthetic pigment contents declined, with a complete loss of PSII photochemical quenching at 1,000 mg(CuO NP) L-1. Oxidative and osmotic stress was evidenced by increased malondialdehyde and proline contents. Elevated expression of ascorbate peroxidase and superoxide dismutase were also observed. Our work clearly demonstrated the toxic effect of Cu accumulation in roots and shoots that resulted in loss of photosynthesis., M. V. J. Da Costa, P. K. Sharma., and Obsahuje seznam literatury
The oxygen-evolving complex (OEC) of Zostera marina is prone to deactivation under visible light, which results in a formation of the long-lived radical P680+. The mechanism to prevent damage caused by P680+ remains unclear. In this study, following light exposure, the upregulation in ascorbate (AsA) content and the presence of PSII cyclic electron flow (PSII-CEF) provide evidence that AsA and PSII-CEF donate electrons to PSII. Furthermore, a factorial design experiment with different combinations of inhibition of AsA and PSII-CEF demonstrates that both inhibition treatments lead to decreases in maximal photochemical yield of PSII, increases in relative variable fluorescence at the K-step, as well as the net loss of PSII reaction center proteins and further degradation of OEC peripheral proteins. These results suggest that AsA and PSII-CEF play photoprotective roles by providing electrons to efficiently prevent damage to PSII from the highly oxidizing radical P680+ in Z. marina.
Infiltration of methyl viologen (MV, source of O2-) and Na-diethyldithiocarbamate (DDC, inhibitor of SOD) into wheat leaves resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus under both moderate and high irradiance. Exogenous antioxidants, ascorbate (ASA) and mannitol, scavenged active oxygen efficiently, protected the photosynthetic system from MV and DDC induced oxidative damage, and maintained high Fv/Fm [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], Fm/F0 (another expression for the maximal photochemical efficiency of PS2), ΦPS2 (actual quantum yield of PS2 under actinic irradiation), qP (photochemical quenching coefficient), PN (net photosynthetic rate), and lowered qNP (non-photochemical quenching coefficient) of the leaves kept under high irradiance and oxidative stress. Phenolic compounds used in these experiments, catechol (Cat), resorcinol (Res), and tannic acid (Tan), had similar anti-oxidative activity and protective effect on photosynthetic apparatus as ASA and mannitol. The anti-oxidative activity and the protective effect of phenolic compounds increased with increase in their concentration from 100 to 300 g m-3. The number and the position of hydroxyl group in phenolic molecules seemed to influence their antioxidative activity. and Hui Jie Zhao, Qi Zou.
Spinach (Spinacia oleracea L. cv. Clermont) leaves grown in open-top chambers and exposed to three different concentrations of ozone were measured for gas exchange, chlorophyll a fluorescence, antioxidant systems, and lipid peroxidation at the end of growing season. High O3 concentration reduced Fv/Fm, indicating that the efficiency in the energy conversion of photosystem 2 (PS2) was altered. The rate of non-cyclic electron transport rate and the capacity to reduce the quinone pool were also affected. The development of non-photochemical quenching was not high enough to decrease the photon excess in the PS2. The limitation of photosynthetic activity was probably correlated with stomata closure and with an increase in intercellular CO2 concentration. Under oxidative stress, superoxide dismutase (SOD) activity was stimulated in parallel with lipid peroxidation. We did not find any differences in the ascorbate (AsA) pool and ascorbate peroxidase (APX) or glutathione reductase (GR) activities between air qualities. Small, but similar responses were observed in spinach leaves exposed to ambient ozone concentration. and A. Calatayud ...[et al.].
This study investigated whether gas exchange and the present content of antioxidant compounds can contribute to the survival of Euterpe oleracea plants in environments of frequent waterlogging. A factorial randomised, experimental design included two distinct water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24 d). Gasexchange parameters, leaf temperature, electrolyte leakage, and contents of antioxidant compounds were measured. Waterlogging did not promote significant alterations in net photosynthetic rate and transpiration, and stomatal conductance was reduced only after 18 d. Malondialdehyde and glutathione contents did not significantly change during waterlogging. Additionally, electrolyte leakage was significant only after 18 d of waterlogging. Thus, this study revealed that maintenance in gas exchange and antioxidant compounds might contribute to the survival of E. oleracea plants in environments exposed to waterlogging., T. S. Pereira, A. K. S. Lobato, G.A.R. Alves, R.N. Ferreira, O.N. Silva, A. P. Martins Filho, E.S. Pereira, L.S. Sampaio., and Obsahuje bibliografii
RNA gel hybridization showed that the expression of monodehydroascorbate reductase (MDHAR) in the wild type (WT) tomato was decreased firstly and then increased under salt- and polyethylene glycol (PEG)-induced osmotic stress, and the maximum level was observed after treatment for 12 h. WT, sense transgenic and antisense transgenic tomato plants were used to analyze the antioxidative ability to cope with osmotic stresses. After salt stress, the fresh mass (FM) and height of sense transgenic lines were greater than those of antisense lines and WT plants. Under salt and PEG treatments, sense transgenic plants showed a lower level of hydrogen peroxide (H2O2) and malondialdehyde (MDA), a higher net photosynthetic rate (PN), and the maximal photochemical efficiency of PSII (Fv/Fm) compared with WT and antisense transgenic plants. Moreover, sense lines maintained higher ascorbate peroxidase (APX) activity than WT and antisense plants under salt- and PEG-induced osmotic stress. These results indicate that chloroplastic MDHAR plays an important role in alleviating photoinhibition of PSII by elevating ascorbate (AsA) level under salt- and PEG-induced osmotic stress., F. Li ... [et al.]., and Obsahuje bibliografii