Involvement of Cell Wall Characteristics in Growth Processes along the Mung Bean Hypocotyl

Abstract

To detect the cell wall characteristics involved in the regulation of growth responses, the composition of wall polysaccharides and the kinetic behaviour of wall-bound glucanases on mung bean hypocotyls were investigated. In the parts of the hypocotyl located below the “elongation zone”, relationships have been shown between the characteristics of pectins and the first phase of auxin- or acid-induced growth responses. Only small pectic molecules with a low calcium content, are compatible with acid-induced wall loosening. The breakage of acid-labile bonds between uronide chains and hemicelluloses is believed to be responsible for the early burst of growth. In young tissues, acid-induced modifications in the cell wall structure might then produce changes in the kinetic behaviour of cell wall polysaccharidases that depend on this structure for support. In old tissues, the number of glycosyl linkages is not sufficient to permit glucanase activities. Enzymatic rupture of covalent bonds may indeed regulate the supply of wall material requisite for sustained growth.