Dehydration-related changes of peroxidase and polyphenol oxidase activity in fronds of the resurrection fern Asplenium ceterach L

Solanum dulcamara L. Berries: A Convenient Model System to Study Redox Processes in Relation to Fruit Ripening

The present study provides, for the first time, a physicochemical and biochemical characterization of the redox processes associated with the ripening of Solanum dulcamara L. (bittersweet) berries. Electron Paramagnetic Resonance Spectroscopy (EPRS) and Imaging (EPRI) measurements of reactive oxygen species (ROS) were performed in parallel with the tissue-specific metabolic profiling of major antioxidants and assessment of antioxidant enzymes activity. Fruit transition from the mature green (MG) to ripe red (RR) stage involved changes in the qualitative and quantitative content of antioxidants and the associated cellular oxidation and peroxidation processes. The skin of bittersweet berries, which was the major source of antioxidants, exhibited the highest antioxidant potential against DPPH radicals and nitroxyl spin probe 3CP. The efficient enzymatic antioxidant system played a critical protective role against the deleterious effects of progressive oxidative stress during ripening. Here, we present the EPRI methodology to assess the redox status of fruits and to discriminate between the redox states of different tissues. Interestingly, the intracellular reoxidation of cell-permeable nitroxide probe 3CP was observed for the first time in fruits or any other plant tissue, and its intensity is herein proposed as a reliable indicator of oxidative stress during ripening. The described noninvasive EPRI technique has the potential to have broader application in the study of redox processes associated with the development, senescence, and postharvest storage of fruits, as well as other circumstances in which oxidative stress is implicated.

Phytochemical Investigation of the Fern Asplenium ceterach (Aspleniaceae)

The fern Asplenium ceterach L. (syn. Ceterach officinarum Willd.) is used in local traditional medicine against kidney stones, gallstones, to facilitate diuresis and to treat benign prostatic hyperplasia. The aim of this study was first to investigate the chemical composition of this fern and then to study the chemical profile of the herbal preparations used in local medicine due to its diuretic properties. In total, nine secondary metabolites from the methanol extract of the aerial parts have been isolated; three flavonoids, namely kaempherol-3- O- β-D-gentiobioside (1), quercetin-3- O- β-D-glucuronide (2), quercetin-3- O- β-D-gentiobioside (3), three phenolic acids, i.e. caffeic acid (4), chlorogenic acid (5) and p-coumaroyl-4- O- β-D-glucoside (6), as well as three phenols, 4-vinyl-phenol-1- O- β-D-glucopyranoside (7), 3-(1- O- β-D-glucopyranosyl-4-hydroxyphenyl)-propionic acid (8), and 4- β- O-D-glucosyl-3,4-dihydroxybenzyl alcohol (9). Moreover, the cyclohexane residue has been submitted to GC-MS and NMR analyses and revealed the presence of ethyl esters of palmitic, linoleic and α-linolenic acids. Finally, based on NMR, TLC and HPLC analyses, it was evident that the chemical fingerprints of all herbal preparations were quite similar, with chlorogenic acid being the main compound and caffeic acid present only in traces.

A water availability gradient reveals the deficit level required to affect traits in potted juvenile Eucalyptus globulus

Background and aims

Drought leading to soil water deficit can have severe impacts on plants. Water deficit may lead to plant water stress and affect growth and chemical traits. Plant secondary metabolite (PSM) responses to water deficit vary between compounds and studies, with inconsistent reports of changes to PSM concentrations even within a single species. This disparity may result from experimental water deficit variation among studies, and so multiple water deficit treatments are used to fully assess PSM responses in a single species.

Methods

Juvenile Eucalyptus globulus were grown for 8 weeks at one of ten water deficit levels based on evapotranspiration from control plants (100 %). Treatments ranged from 90 % of control evapotranspiration (mild water deficit) to 0 % of control evapotranspiration (severe water deficit) in 10 % steps. Plant biomass, foliar abscisic acid (ABA) levels, Ψ leaf , leaf C/N, selected terpenes and phenolics were quantified to assess responses to each level of water deficit relative to a control.

Key Results

Withholding ≥30 % water resulted in higher foliar ABA levels and withholding ≥40 % water reduced leaf water content. Ψ leaf became more negative when ≥60 % water was withheld. Plant biomass was lower when ≥80 % water was withheld, and no water for 8 weeks (0 % water) resulted in plant death. The total oil concentration was lower and C/N was higher in dead and desiccated juvenile E. globulus leaves (0 % water). Concentrations of individual phenolic and terpene compounds, along with condensed tannin and total phenolic concentrations, remained stable regardless of water deficit or plant stress level.

Conclusions

These juvenile E. globulus became stressed with a moderate reduction in available water, and yet the persistent concentrations of most PSMs in highly stressed or dead plants suggests no PSM re-metabolization and continued ecological roles of foliar PSMs during drought.

Responses to mild water deficit and rewatering differ among secondary metabolites but are similar among provenances within Eucalyptus species

Water deficit associated with drought can severely affect plants and influence ecological interactions involving plant secondary metabolites. We tested the effect of mild water deficit and rewatering on physiological, morphological and chemical traits of juvenile Eucalyptus globulus Labill. and Eucalyptus viminalis Labill. We also tested if responses of juvenile eucalypts to water deficit and rewatering varied within species using provenances across a rainfall gradient. Both species and all provenances were similarly affected by mild water deficit and rewatering, as only foliar abscisic acid levels differed among provenances during water deficit. Across species and provenances, water deficit decreased leaf water potential, above-ground biomass and formylated phloroglucinol compound concentrations, and increased condensed tannin concentrations. Rewatering reduced leaf carbon : nitrogen, and total phenolic and chlorogenic acid concentrations. Water deficit and rewatering had no effect on total oil or individual terpene concentrations. Levels of trait plasticity due to water deficit and rewatering were less than levels of constitutive trait variation among provenances. The overall uniformity of responses to the treatments regardless of native provenance indicates limited diversification of plastic responses when compared with the larger quantitative variation of constitutive traits within these species. These responses to mild water deficit may differ from responses to more extreme water deficit or to responses of juvenile/mature eucalypts growing at each locality.

Metabolic profiling of the resurrection plant Haberlea rhodopensis during desiccation and recovery

Desiccation tolerance is among the most important parameters for crop improvement under changing environments. Resurrection plants are useful models for both theoretical and practical studies. We performed metabolite profiling via gas chromatography coupled with mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) and analyzed the antioxidant capacity of the endemic resurrection plant Haberlea rhodopensis at desiccation and recovery. More than 100 compounds were evaluated. Stress response included changes in both primary and secondary metabolic pathways. The high amounts of the specific glycoside myconoside and some phenolic acids - e.g. syringic and dihydrocaffeic acid under normal conditions tend to show their importance for the priming of H. rhodopensis to withstand severe desiccation and oxidative stress. The accumulation of sucrose (resulting from starch breakdown), total phenols, β-aminoisobutyric acid, β-sitosterol and α-tocopherol increased up to several times at later stages of desiccation. Extracts of H. rhodopensis showed high antioxidant capacity at stress and normal conditions. Myconoside was with the highest antioxidant properties among tested phenolic compounds. Probably, the evolution of resurrection plants under various local environments has resulted in unique desiccation tolerance with specific metabolic background. In our case, it includes the accumulation of a relatively rare compound (myconoside) that contributes alone and together with other common metabolites. Further systems biology studies on the involvement of carbohydrates, phenolic acids and glycosides in the desiccation tolerance and antioxidant capacity of H. rhodopensis will definitely help in achieving the final goal - improving crop drought tolerance.

Antioxidant response of Stevia rebaudiana B. to polyethylene glycol and paclobutrazol treatments under in vitro culture

This investigation was carried out with the aim of determining the effect of paclobutrazol (PBZ) (0 and 2 mg l(-1)) and polyethylene glycol (PEG) (0, 2, 4 and 6 % w/v of PEG 6000) treatments on antioxidant system of Stevia rebaudiana Bertoni under in vitro condition. Analysis of data showed that PEG treatment significantly increased hydrogen peroxide (H2O2) and phenolic contents, while PBZ treatment limited the effect of PEG on them. Our data revealed that PEG treatment significantly increased total antioxidant capacity, catalase (CAT), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and peroxidase (POD) activity, while it inversely decreased glutathione reductase (GR) activity. The superoxide dismutase (SOD) activity was not affected by PEG treatment. PBZ treatment induced significantly higher levels of CAT and GR activity and lower levels of SOD activity in PEG-treated plants. PBZ in combination with PEG resulted in no significant difference on APX activity with PEG treatment alone. PBZ treatment prevented the effect of PEG on the PPO activity. PEG (with or without PBZ) treatment increased the ascorbate pool, whereas total glutathione level was not affected by PEG. Our finding indicated that PBZ reduced the negative effect of PEG treatment by quenching H2O2 accumulation and increasing the CAT activity. Collectively, the antioxidant capacity of S. rebaudiana in PEG treatment condition was associated with active enzymatic and non-enzymatic defence systems which partly could be improved by the PBZ treatment. In addition, a higher accumulation of phenolic compounds leads to a more potent reactive oxygen species scavenging activity in S. rebaudiana.

Peroxidase and polyphenol oxidase activity in moderate resistant and susceptible Vicia faba induced by Aphis craccivora (Hemiptera: Aphididae) infestation

Two faba bean, Vicia faba L., cultivars, Gazira2 and Misr1, representing cultivars moderately resistant and susceptible to aphids, were analyzed for peroxidase (POD) and polyphenol oxidase (PPO) activities induced by cowpea aphid, Aphis craccivora Koch. infestation. Two tissue types (whole plant [WP] and detached leaf [DL]), two infestation status (infested and uninfested), and three aphid infestation durations (1, 3, and 5 d) were considered in POD and PPO data analysis. Factorial analysis showed that only cultivar factor has a significant effect on both POD and PPO activity, especially on the first day after aphid infestation (P: 0.0003 and 0.001, respectively). Tissue type has no significant effect, indicating either DL or WP can be used for measuring POD and PPO activities. While the unsignificant different of infestation status reflecting a constitutive resistant character in Gazira2. Mann-Whitney U-test showed that POD and PPO activities in Gazira2 were higher significantly when compared with Misr1 with P value 0.0006 and 0.0015 for POD and PPO, respectively. Repeated measures analysis indicates that the POD and PPO activities on Gazira2 were significantly higher when compared with Misr1. Additionally, POD activity changed significantly over the time in 1, 3, and 5 d after aphid infestation. We concluded that higher activity of POD and PPO in cultivar Gazira2 is strongly associated with their resistant characters.