Net electrolyte efflux from suspension-cultured tobacco cells undergoing the hypersensitive reaction to Pseudomonas syringae pv. pisi resulted from a specific efflux of K which was accompanied by an equimolar net influx of H+. These fluxes began 60 to 90 minutes after inoculation of tobacco cells with bacteria, reached maximum rates of 6 to 9 micromoles per gram fresh weight tobacco cells per hour within 2.5 to 3 hours, and dropped below 4 micromoles per gram per hour within 5 hours. Tobacco cells lost approximately 35% of total K' during this period, and average cellular pH declined by approximately 0.75 pH unit. These events were accompanied by a 30% decrease in cellular ATP. K+ and H' fluxes were inhibited by the protonophore (p-trifluoromethoxy)carbonyl cyanide phenylhydrazone and by increasing the K' concentration of the external solution. Tobacco leaf discs inoculated with the bacterium also exhibited a specific net K+ efflux and H+ influx. These results suggest that induction of the hypersensitive reaction in tobacco proceeds through the activation of a passive plasmalemma K+/H+ exchange mechanism. It is hypothesized that activation of this exchange is a major contributing factor in hypersensitive plant cell death.The hypersensitive reaction is characterized by the rapid death ofindividual plant cells which come into contact with pathogenic organisms, and is generally associated with disease resistance of the whole plant to the pathogen (1 1, 13, 14). The capacity to express the HR3 appears to be universal among highet plants and can be triggered by bacterial, fungal, viral, and nematode pathogens. Despite its close association with resistance, the HR and its role in pathogen localization are not well understood. It has even been argued that hypersensitivity is a consequence rather than a cause ofdisease resistance (1 1 for 16 to 20 h before each experiment. Bacteria were suspended in standard assay medium (0.175 M mannitol, 0.5 mm K2SO4, 0.5 mm CaCl2, 5 mm Mes adjusted to pH 6.0 with Tris), washed twice by centrifugation, and resuspended in this medium to an inoculum density of 8 x 109 viable bacteria/ml unless otherwise stated. Suspension-cultured tobacco cells were derived from Nicotiana tabacum var Hicks (10) and maintained as previously described (3). Cells were collected by filtration from logarithmically growing cultures, washed with 10 ml assay medium/g fresh weight tobacco, and resuspended in 28.5 ml assay medium/g tobacco. Cell suspensions were incubated in 50-ml beakers at 27°C on a reciprocal shaker at 150 oscillations/min for approximately 1 h. This preincubation period was necessary for consistent induction of the HR. Tobacco cell suspensions were then inoculated with 1.5 ml bacterial suspension/g tobacco. This

Myosin polymerization and formation of ε-(␥-glutamyl)lysine linkages were quantified in Alaska pollock surimi gels which contained no additive (control), or a commercial microbial transglutaminase (MTGase). As preincubation (''setting'') time at 25ЊC was increased, the gel strength of control and 0.2% MTGase-added samples increased, with greater increases at higher MTGase levels. SDS-PAGE and HPLC analyses showed increasing nondisulfide polymerization and ε-(␥-glutamyl)lysine dipeptide content, with increasing setting time and/or added MTGase. Content of ε-(␥-glutamyl)lysine dipeptide correlated with gel strength (shear stress) and shear modulus at failure (G f ) for these gels. Higher stresses were measured in samples containing 0.2% MTGase than in controls at corresponding levels of ε-(␥-glutamyl)lysine dipeptide, indicating that rate of myosin polymerization may affect ultimate gel strength.

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A myosin/actomyosin mixture (MAM), actomyosin and myosin were isolated from post-rigor turkey. Rheological properties of MAM gels were determined by uniaxial compression. Breast MAM formed gels which were stable at lower protein concentrations (10 and 15 mg/mL) than thigh MAM (20 and 25 mg/mL). Differential scanning calorimetry (DSC) and a fluorescent hydrophobic probe, 8-anilino-l-napthalene sulfonate (ANS), were used to study thermal transitions. One DSC peak was observed in breast and thigh MAM. ANS thermograms showed that thigh actomyosin had a greater transition temperature (Tr) (518°C) than breast actomyosin (49.7"C). The ANS Tr was 48°C for both myosins. The difference in gelation appeared to be associated with protein-protein interactions.