Critical exponents of protonic percolation in maize seeds

The hydration-dependent dc conductivity of the two main components (embryo and endosperm) of a viable maize seed has been measured by a dielectric-gravimetric technique. The protonic conductivity, plotted as a function of the sample water content, displays a percolative behavior characterized by a threshold and by a critical exponent in agreement with theory for a two-dimensional process. This percolative water-assisted process reflects the presence of an extended network of water molecules adsorbed on the surface of proteins and/or membranes inside intact cells. Moreover, the percolation threshold is found close to the onset of the biological function of these tissues, where the early enzymatic activity leads to the onset of metabolism, a prerequisite to the commencement of germination.