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 r oots. Low pH, ranging from pH 3-4.5, induces rapid elongation of excised ro ots, a phenomenon known as acid growth. The creep-extension analysis was ca rried 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 sati vum L. cv. Alaska) and described by the physical parameters of three elasti c (E-0, E-1, E-2) and three viscosity (eta (0), eta (1), eta (2)) parameter s 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. Amo ng the parameters, E-0 and eta (0) were the most significant parameters to represent the whole extensibility of the roots. The parameter eta (0) marke dly declined in response to the environmental low pH (acid growth), whereas other parameters were not much affected by low pH. Relationship between th e change in these physical parameters and the change in cell wall extensibi lity under low pH was discussed in order to elucidate the rheological proce sses taking place in the elongating cell walls.