Materials and methods
2.1. Plant material
2.1.1. Diffusion
Fresh spinach and green beans were bought at a local supermarket on the day of the experiments, or stored at 4 °C for maximum of 48 h after purchase. Spinach and green beans were first blanched in phosphate buffer pH 7 (0.01 mol/l) or in citrate phosphate buffer pH 5 (0.01 mol/l) for 10 min at 100 °C with solid–liquid ratio of 50 and 100 g/l, respectively, in order to inactivate enzymes and destroy cell compartmentalization. After blanching, spinach and green beans were drained, weighted and immediately put into a large receptacle (with the same solid–liquid ratio of 50 g/l), to start the diffusion.