Hydrogen peroxide protects tobacco from oxidative stress by inducing a set of antioxidant enzymes.

Tolerance against oxidative stress generated by high light intensities or the catalase inhibitor aminotriazole (AT) was induced in intact tobacco plants by spraying them with hydrogen peroxide (H2O2). Stress tolerance was concomitant with an enhanced antioxidant status as reflected by higher activity and/or protein levels of catalase, ascorbate peroxidase, guaiacol peroxidases, and glutathione peroxidase, as well as an increased glutathione pool. The induced stress tolerance was dependent on the dose of H2O2 applied. Moderate doses of H2O2 enhanced the antioxidant status and induced stress tolerance, while higher concentrations caused oxidative stress and symptoms resembling a hypersensitive response. In stress-tolerant plants, induction of catalase was 1.5-fold, that of ascorbate peroxidase and glutathione peroxidase was 2-fold, and that of guaiacol peroxidases was approximately 3-fold. Stress resistance was monitored by measuring levels of malondialdehyde, an indicator of lipid peroxidation. The levels of malondialdehyde in all H2O2-treated plants exposed to subsequent high light or AT stress were similar to those of unstressed plants, whereas lipid peroxidation in H2O2-untreated plants stressed with either high light or AT was 1.5- or 2-fold higher, respectively. Although all stress factors caused increases in the levels of reduced glutathione, its levels were much higher in all H2O2-pretreated plants. Moreover, significant accumulation of oxidized glutathione was observed only in plants that were not pretreated with H2O2. Extending the AT stress period from 1 to 7 days resulted in death of tobacco plants that were not pretreated with H2O2, while all H2O2-pretreated plants remained little affected by the prolonged treatment. Thus, activation of the plant antioxidant system by H2O2 plays an important role in the induced tolerance against oxidative stress.

Swine cell systems as interferon producers. IV. Comparative studies on the correlation between virulence of different Newcastle disease virus strains and their potency as interferon inducers.

Comparative studies concerning a correlation between virulence of various Newcastle virus strains and their interferon-inducing potency confirmed that such a correlation existed. The nearly avirulent La Sota strain of NDV was the poorest interferon inducer, the virulent Hertfordshire strain manifested a very good inducing potency. However, the most virulent J.B. strain virus was a poorer interferon inducer than the Hertfordshire strain. This should not be viewed as contradictory to the conclusion of the correlation between virulence and interferon-inducing ability of NDV since the highly virulent strain might destroy faster the interferon-producing cells, before the latter produced the maximum interferon quantity which they potentially could produce.