Changes in ascorbate and glutathione levels and in activities of ascorbate peroxidase, catalase, dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and superoxide dismutase (SOD) were investigated in tobacco mosaic virus (TMV)-inoculated lower leaves and in non-inoculated upper leaves of Nicotiana tabacum L. cv Xanthi-nc. In separate experiments the effects of exogenous salicylic acid (SA) were also studied. Symptom appearance after TMV inoculation was preceded by a slight, transient decline of ascorbate peroxidase, GR, GST, and SOD activities in the inoculated lower leaves, but after the onset of necrosis these activities and the glutathione level substantially increased. Ascorbic acid level and DHAR activity declined and dehydroascorbate accumulated in the inoculated leaves. In upper leaves, the glutathione level and the activities of GR, GST, and SOD increased 10 to 14 d after TMV inoculation of the lower leaves, concomitantly with the development of systemic acquired resistance. From the six distinct SOD isoenzymes found in tobacco leaves, only the activities of Cu,Zn-SOD isoenzymes were affected by TMV. SA injection induced DHAR, GR, GST, and SOD activities. Catalase activities were not modified by TMV infection or SA treatment. It is supposed that stimulated antioxidative processes contribute to the suppression of necrotic symptom development in leaves with systemic acquired resistance.

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The adsorption of a cationic surfactant, dodecyltrimethylammonium bromide (C 12 TAB), from aqueous solutions on graphitized carbon black has been investigated from 288.15 to 318.15 K using a versatile, automated measuring system, which has been designed for the simultaneous measurement of the adsorption isotherm and the calorimetric enthalpies of displacement at the solid/liquid interface. At low concentrations, the surfactant molecules form a flat monolayer on the graphite surface. The enthalpy of monolayer formation is apparently not (or only slightly) dependent on the temperature and is independent of the surface coverage (-61 kJ‚mol -1 ). The adsorption proceeds further as the concentration in the bulk solution is increased to the cmc. In this region, the enthalpy of displacement is again nearly independent of the surface coverage but depends strongly on the temperature: -10.7, -17.5, and -29 kJ‚mol -1 at 288.15, 298.15, and 318.15 K, respectively. The mechanism of the adsorption and the morphology of the high-density adsorbate structure have been analyzed in terms of the classical reorientation model (reorientation of the adsorbed surfactant molecules from a horizontal to a vertical orientation, accompanied by further adsorption from the bulk solution) and in terms of a recent concept of interfacial aggregation (formation of half-cylindrical surface micelles templated by an epitaxially bound surfactant monolayer). The results of the thermodynamic analysis strongly support the formation of C 12 TAB half-cylinders at the graphite/water interface.