Altered Cell Microfibrillar Orientation in Ethylene-treated Pisum sativum Stems

Abstract

The roots and stems of plants typically swell when they are exposed to ethylene (1-3, 5, 8), or supraoptimal auxin (2, 3, 5, 8, 20), and root hairs are induced to form (1, 5, 6, 8). When supraoptimal IAA causes pea subapical stem sections to swell, the optical birefrigence pattern of the cell wall changes, and newly deposited wall microfibrils tend to be oriented in a longitudinal rather than radial direction (20, 21). Ethylene also alters the birefrigence of pea stem subapical cell walls when it causes the tissue to swell (3, 4, 9), producing a characteristic banded pattern. This same pattern occurs in pea stem tissue which has swelled after treatment with supraoptimal IAA (4, 9). The similar effects of ethylene and supraoptimal IAA on pea tissue have been attributed to the fact that supraoptimal IAA induces ethylene formation (2, 3). According to the multinet hypothesis (13, 19), cells elongate predominantly in a longitudinal direction because of the re-straining influence of newly deposited, radially oriented micro-fibrils. If a cell is to expand radially under the influence of ethylene or supraoptimal IAA, newly deposited microfibrils no longer should be oriented in a radial direction. The pres-ent communication describes the effect of ethylene on micro-fibrillar organization in various regions of the cell wall, and shows it to be similar to that resulting from auxin treatment (20, 21). Pea seedlings were grown in vermiculite for 7 days in com-plete darkness and then treated continuously in a desiccator