In order to understand the role of cytosolic antioxidant enzymes in drought stress protection, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants overexpressing cytosolic Cu/Zn-superoxide dismutase (cytsod) (EC 1.15.1.1) or ascorbate peroxidase (cytapx) (EC 1.11.1.1) alone, or in combination, were produced and tested for tolerance against mild water stress. The results showed that the simultaneous overexpression of Cu/Znsod and apx or at least apx in the cytosol of transgenic tobacco plants alleviates, to some extent, the damage produced by water stress conditions. This was correlated with higher water use efficiency and better photosynthetic rates. In general, oxidative stress parameters, such as lipid peroxidation, electrolyte leakage, and H₂O₂ levels, were higher in non-transformed plants than in transgenic lines, suggesting that, at the least, overexpression of cytapx protects tobacco membranes from water stress. In these conditions, the activity of other antioxidant enzymes was induced in transgenic lines at the subcellular level. Moreover, an increase in the activity of some antioxidant enzymes was also observed in the chloroplast of transgenic plants overexpressing cytsod and/or cytapx. These results suggest the positive influence of cytosolic antioxidant metabolism on the chloroplast and underline the complexity of the regulation network of plant antioxidant defences during drought stress.

In a previous publication, we showed that the treatment of pea seeds in the presence of hydrogen peroxide (H₂O₂) increased germination performance as well as seedling growth. To gain insight into the mechanisms responsible for this behaviour, we have analysed the effect of treating mature pea seeds in the presence of 20 mm H₂O₂ on several oxidative features such as protein carbonylation, endogenous H₂O₂ and lipid peroxidation levels. We report that H₂O₂ treatment of the pea seeds increased their endogenous H₂O₂ content and caused carbonylation of storage proteins and of several metabolic enzymes. Under the same conditions, we also monitored the expression of two MAPK genes known to be activated by H₂O₂ in adult pea plants. The expression of one of them, PsMAPK2, largely increased upon pea seed imbibition in H₂O₂, whereas no change could be observed in expression of the other, PsMAPK3. The levels of several phytohormones such as 1‐aminocyclopropane carboxylic acid, indole‐3‐acetic acid and zeatin appeared to correlate with the measured oxidative indicators and with the expression of PsMAPK2. Globally, our results suggest a key role of H₂O₂ in the coordination of pea seed germination, acting as a priming factor that involves specific changes at the proteome, transcriptome and hormonal levels.

Summary: To fortify the antioxidant capacity of plum plants, genes encoding cytosolic antioxidants ascorbate peroxidase (cytapx) and Cu/Zn‐superoxide dismutase (cytsod) were genetically engineered in these plants. Transgenic plum plants expressing the cytsod and/or cytapx genes in cytosol have been generated under the control of the CaMV35S promoter. High levels of cytsod and cytapx gene transcripts suggested that the transgenes were constitutively and functionally expressed. We examined the potential functions of cytSOD and cytAPX in in vitro plum plants against salt stress (100 mm NaCl). Several transgenic plantlets expressing cytsod and/or cytapx showed an enhanced tolerance to salt stress, mainly lines C5‐5 and J8‐1 (expressing several copies of sod and apx, respectively). Transformation as well as NaCl treatments influenced the antioxidative metabolism of plum plantlets, including enzymatic and nonenzymatic antioxidants. Transgenic plantlets exhibited higher contents of nonenzymatic antioxidants glutathione and ascorbate than nontransformed control, which correlated with lower accumulation of hydrogen peroxide. Overall, our results suggest that transformation of plum plants with genes encoding antioxidant enzymes enhances the tolerance to salinity.

The imbibition of pea seeds with hydrogen peroxide (H2O2) increased the germination as well as the seedling growth, producing an invigoration of the seeds. We propose that H2O2 could acts as signal...