A simple measurement of the pH of root apoplast by the fluorescence ratio method

We present a simple procedure for measuring the pH in the apoplast of the rice root, using the fluorescent ratio method and Oregon Green 488 (OG). Staining with 5 mu M OG for 3 min followed by 5-min washing with calcium solution was an effective method for measuring the pH of the apoplast at the root surface. Diffusion of OG from the apoplast could be prevented by circulating a low concentration of OG (0.02 mu M) in the root vessel. However, aluminum ions disturbed the pH measurement. In the presence of 50 mu M AICI(3), the pH value was inaccurate at values higher than pH 5.0.