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.

The critical micelle concentrations and the enthalpies of micelle formation of n-octyl tetraethylene glycol monoether (C8E4) and n-octyl β-D-monoglucoside (C8G1) in water have been determined at 298.15 K by titration microcalorimetry. The adsorption and thermal behavior of these nonionic surfactants at the hydrophilic silica glass/aqueous solution interface have been investigated by simultaneous measurements of the adsorption isotherm and the calorimetric enthalpies of displacement in a flow system. Both surfactants display pronounced cooperative adsorption behavior (S-shaped isotherms). While in the low-affinity region the amount adsorbed and the integral enthalpies of displacement are only slightly smaller for C 8G1 than for C8E4, the deviation increases to 1 order of magnitude in the aggregative adsorption region. The observed difference in the adsorption behavior is interpreted in terms of the different hydrophilic head groups of the two amphiphiles. The differential molar enthalpies of displacement are comparable in magnitude in both the low-affinity (exotherm) and aggregative (endotherm) regimes. The molar enthalpies of aggregate formation at the silica/water interface were found to be close to those in the bulk solution, indicating that surface aggregation and bulk micellization are very similar phenomena. The enthalpy/entropy balance of the formation of the adsorption layer has been described in terms of thermodynamic potential functions.

Transgenic tobacco plants that synthesize alfalfa ferritin in vegetative tissues--either in its processed form in chloroplasts or in the cytoplasmic nonprocessed form--retained photosynthetic function upon free radical toxicity generated by iron excess or paraquat treatment. Progeny of transgenic plants accumulating ferritin in their leaves exhibited tolerance to necrotic damage caused by viral (tobacco necrosis virus) and fungal (Alternaria alternata, Botrytis cinerea) infections. These transformants exhibited normal photosynthetic function and chlorophyll content under greenhouse conditions. We propose that by sequestering intracellular iron involved in generation of the very reactive hydroxyl radicals through a Fenton reaction, ferritin protects plant cells from oxidative damage induced by a wide range of stresses.

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The material and enthalpy balances of the adsorption of sodium n-decyl sulfate from aqueous solutions onto graphitized carbon black were determined between 288 and 318 K by using an automated flow sorption/ microcalorimeter system. At low concentrations, the surfactant molecules form a flat monomolecular film on the graphite plane, in consequence of surface-directed ordering. A mechanism is proposed in which two adsorbed phases coexist during the formation of this surfactant monolayer. The enthalpy of adsorption in the monolayer region is ca. -42 kJ mol -1 , which does not depend appreciably on the temperature or on the surface coverage. At higher concentrations, the ordered monolayer induces surface aggregation to produce half-cylindrical hemimicelles as the critical micelle concentration is approached. The enthalpies of surface aggregation at 288, 298, and 318 K are -10, -16, and -26 kJ mol -1 , respectively. As the temperature is increased from 288 to 318 K, the average number of surfactant molecules in the cross section of a half-cylinder drops from ca. 5.4 to 3.4. Calorimetric evidence is provided that cationic and anionic surfactant adsorption on graphite follow the same mechanism in the low-density and high-density adsorbate regions.