Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 mM NaCl) on protective enzyme activities under ambient (350 micromol mol(-1)) and elevated (700 micromol mol(-1)) CO(2) concentrations were investigated in two barley cultivars (Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO(2), upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO(2) alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO(2) and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO(2) mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.

Raphanus sativus L. cv. Rimbo was grown for 10 days after emergence in hydroponic culture containing 0.12 (control), 5, 10 and 15 micro M copper. The seeds were germinated in the presence of the copper solution. The Cu contents increased with the treatment in both shoots and roots, maintaining in the roots a value eight- to ten-fold higher than in the shoots. With the treatment both shoots and roots underwent growth inhibition and an increase in the percentage of dry weight. Membrane damage and lipid peroxidation increased and glutathione was oxidized as the copper concentration increased, indicating an acceleration of oxidative processes. Control shoots had high contents of reduced glutathione and low contents of phytochelatin-SH whereas roots showed an opposite pattern, suggesting an utilization of reduced glutathione for phytochelatin synthesis. In both parts phytochelatin-SH content reached the maximum at 5 micro M copper and then decreased, reaching at 15 micro M copper the control value in the roots and a value five-fold higher than the control value in the shoots. The main phenolic acids represented in R. sativus were chlorogenic, vanillic, caffeic, siringic, p-coumaric and ferulic acids whereas the least represented were gallic, protocatechuic and p-hydroxybenzoic acids. The phenolic acids as well as the total and reduced ascorbate contents increased with the intensification of copper treatment. Notwithstanding these changes, total ascorbate remained 35% higher in the shoots than in the roots. The reduced ascorbate was thus able to replenish reducing equivalents to phenoxyl radicals thus explaining the increase in the phenolic compounds.

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The aim of the present research was to study the effects of olive leaf addition (0 and 3%) on the major antioxidants and the antioxidant activity of Neb Jmel and Oueslati olive oils. Olives and leaves of the two Tunisian varieties were harvested during the 2016/2017 crop season. Both leaves and oils were characterised for their concentrations in phenolics, tocopherols and antioxidant power. Other parameters such as free acidity, peroxide value, chlorophyll and carotenoid concentrations were also taken into consideration. Compared to Oueslati, the Neb Jmel oil showed a lower free acidity (50%) and peroxide value (5.6-fold), and higher chlorophyll (1.6-fold), total phenolics (1.3-fold), flavonoid (3-fold) and oleuropein derivative (1.5-fold) concentrations, in addition to an increased antioxidant activity (1.6-fold). Leaf addition promoted a significant increment in total chlorophyll, α-tocopherol and phenolics in both varieties, above all in Oueslati oil, due to a higher abundance of bioactive constituents in the corresponding leaves. In particular, chlorophyll and carotenoid concentrations reached values twice higher than in Neb Jmel leaves, and flavonoids and oleouperin derivatives were three-fold higher. This prevented the oxidation and the formation of peroxides, reducing the peroxide value of the fortified oil to the half. The results provide evidence on the performance of the Tunisian Neb Jmel and Oueslati varieties, showing that their oils present a chemical profile corresponding to the extra virgin olive oil category and that, after leaf addition, their nutritional value was improved.

Sunflower seedlings (Helianthus annuus cv. Licia Stella) reached a mild, moderate and severe level of water deficit stress after 5, 8 and 11 days of soil water depletion, respectively. At a moderate level of water deficit stress, an elastic adjustment occurred. At the same time, in response to a minor osmotic potential (Ψπ) and an intermediate rate of water potential (Ψw) decrease, glutathione level increased and enzyme activities related to the ascorbate/glutathione cycle were induced. At severe water deficit stress, the efficiency of this defence mechanism fell, oxidative processes intensified and soluble protein content decreased further. The results of the present experiments suggest that during water deficit stress the water status of the plants plays a key role in the activation of defence mechanisms.

Ramonda serbica plants dehydrated for 14 days reached a relative water content of 4.2% and entered into anabiosis prior to being rehydrated for 48 h. Total ascorbate (AsA + DHA) and glutathione (GSH + GSSG) contents increased during dehydration and approached control values by the end of rehydration. Reduced ascorbate (AsA) and glutathione (GSH) were consumed during the first 13 days of dehydration when guaiacol‐, syringaldazine‐ and phenolic peroxidases (EC 1.11.1.7) increased. At the end of dehydration AsA and GSH accumulated whereas peroxidases decreased to half the value of controls. In this period, plants of R. serbica face a phase of reduced metabolism and, thus, of reduced consumption of antioxidants. During rehydration, both AsA and GSH were utilized reaching, after 48 h, about 20 and 40% of their total pools, respectively; moreover peroxidases increased showing the recovery of metabolic activities. In the dehydration process total phenolic acids decreased, but accumulated after 5 h of rehydration and returned to control values at the end of rehydration. In R. serbica leaves, the most representative phenolic acids were protocatechuic, p‐hydroxybenzoic and chlorogenic acids. Most concentrated phenolic acids, such as protocatechuic and chlorogenic acids, accumulated during the first period of rehydration when AsA decreased. These results suggest a role of ascorbate in inhibiting oxidation when phenolic peroxidases remain at low levels. As a consequence of this inhibition, ascorbate was oxidized and when most of it was consumed, oxidation of phenols resumed.

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