Figure 5.

Ratiometric real-time quantitation of spatial leaf apoplastic pH gradients in response to 20 mM NaCl stress added to the roots. (A) Leaf apoplastic pH response was discriminated within three apoplastic components, viz. in the stomatal cavitiy (n = 9 ROI; green kinetic; mean ± SE of ROIs), in the epidermal apoplast (n = 20 ROI; red kinetic; mean ± SE of ROIs) and in the apoplast surrounding the palisade mesophyll (n = 20 ROI; blue kinetic; mean ± SE of ROIs). Black arrow indicates the time of the addition of the 20 mM NaCl stress stimulus into the nutrient solution. Ratiometric images (B–E) show the time series of apoplastic leaf pH at (B) 25, (C) 50, (D) 110 min, and (E) 170 min after measurement had started (time of image acquisition is presented in the upper right corner). Ratios were color-coded on a spectral color scale (see lookup-table as inset in B). The ratio images under the most alkaline conditions suggest that fluorescent signals come directly from the palisade cells as indicated by the # in (D). This phenomenon is explained in section “Discussion.” Representative kinetics of four equivalent recordings of plants gained from independent experiments.