Susceptibility of plants to potato virus X accumulation in directly inoculated and systemically infected leaves is altered by modification of alternative respiratory pathway capacity. (A) Semi-quantitative analysis of virus accumulation in PVX-inoculated non-transgenic and Aox-transgenic plants by immunoblot analysis using anti-PVX coat protein (CP). This showed that virus accumulation was higher in directly-inoculated and systemically-infected leaves of plants with increased AP capacity than in corresponding tissues of non-transgenic plants. (B) Quantitative analysis (enzyme-linked immunosorbent assay) of PVX coat protein accumulation in non-transgenic (NT) plants and plants belonging to transgenic lines with increased (↑) or decreased (↓) AP capacity. Systemically-infected (i.e., upper, not directly-inoculated) leaf tissue was harvested at 14 days post-inoculation. Tissue from the fourth leaf above the inoculated leaf was taken in each case. Using a standard curve normalized with purified PVX, mean virus concentrations per gram of leaf tissue were determined and the data from one experiment, out of a total of three independent experiments, are plotted above showing a significant (t-test, p < 0.05) difference in PVX accumulation in plants with decreased AP capacity compared with those with increased AP capacity. The number of samples was six for each plant line (one sample = one plant) in each treatment group. Error bars represent mean ± standard error of the mean.