Orientation of cell growth in the etiolated pea stem : Effect of ethylene and auxin on cell wall deposition.

Both ethylene and IAA induce swelling in the sub-apical region of etiolated pea plants. The modified cells of these two types of swellings differ both morphologically and in their enzyme composition. In ethylene the cell walls become thickened within 24 h and the level of peroxidase is enhanced; ethylene does not affect cellulase levels. IAA induced swellings are not accompanied by early thickening of cell walls or enhanced peroxidase activity, but IAA greatly increases the level of cellulase. It is proposed that the retardation of extension growth by ethylene treatment results from the deposition of longitudinal microfibrils in the walls and that cross linking bonds in the polysaccharide matrix prevent their separation. Lateral expansion can occur, however, in the presence of auxin-induced cellulase which breaks or prevents the formation of these bonds.