Effect of Gibberellic Acid and Ethylene on Peroxidase in Pea Internodes

Abstract

Ethylene at 5–80 μl l⁻¹ inhibited elongation and induced swelling in internodes of light-grown normal and dwarf pea plants; GA₃ did not prevent swelling in response to ethylene. GA₃ neither inhibited nor enhanced the activity of isoperoxidases in the internodes, regardless of its effect on their elongation. Ethylene at 80 μl l⁻¹ enhanced peroxidase in GA₃-untreated and treated normal and dwarf plants. At 5 μl l⁻¹, ethylene had only a weak effect on peroxidase activity or none. The enzyme enhancement by ethylene was not related to its effect on cell expansion and seems do be due, at least in part, to chemical injury. Electron microscopy revealed peroxidase activity in the rough ER and cell walls, including intercellular spaces. Staining of walls in ethylene-treated tissues was more pronounced than in untreated ones. Golgi vesicles did not seem to be involved in the assembly of the enzyme carbohydrate moiety in ethylene-treated cells. The peroxidase fraction extracted with 20 mM phosphate buffer, pH 6, and that extracted from wall debris with 1 M NaCl accounted for 98% of total enzyme activity. Both fractions contained the same six cathodic isoforms which comprised 85–90% of their activity. Electrophoresis did not reveal differences in the qualitative isoenzyme patterns in relation to variety, age, GA₃, or ethylene. The only observed quantitative differences were age-dependent. Procedural artefacts during separation of protoplast and wall ionically bound peroxidase fractions are discussed.