Measurement of viscoelastic properties of root cell walls affected by low pH in lateral roots of Pisum sativum L.

Mechanical extensibility of the cell wall limits the elongation growth of roots. Low pH, ranging from pH 3–4.5, induces rapid elongation of excised roots, a phenomenon known as acid growth. The creep-extension analysis was carried out to measure and elucidate the viscoelastic properties of root cell walls in the acidic environment in vitro. The viscoelastic properties were determined at the elongation zone of the lateral roots of pea (Pisum sativumL. cv. Alaska) and described by the physical parameters of three elastic (E₀, E₁, E₂) and three viscosity (₀, ₁, ₂) parameters using a Kelvin–Voigt–Burgers' model. The present method could measure the viscoelasticity of 1-mm long root zones from 2 to 9 mm behind the tip. Among the parameters, E₀ and ₀ were the most significant parameters to represent the whole extensibility of the roots. The parameter ₀ markedly declined in response to the environmental low pH (acid growth), whereas other parameters were not much affected by low pH. Relationship between the change in these physical parameters and the change in cell wall extensibility under low pH was discussed in order to elucidate the rheological processes taking place in the elongating cell walls.