Development of Epidermal Cell Wall Peroxidases along the Mung Bean Hypocotyl: Possible Involvement in the Cell Wall Stiffening Process

Abstract

Goldberg, R., Liberman, M., Mathieu, C, Pierron, M. and Catesson, A. M. 1987. Development of epidermal cell wall peroxidases along the mung bean hypocotyl: possible involvement in the cell wall stiffening process.—J. exp. Bot. 38: 1378–1390. Ultrastructural investigation showed that in the epidermis of mung bean hypocotyls, cell wall peroxidatic activities could be detected mainly below the maximal elongation zone. In the epidermis the peroxidatic activities were preferentially located in the radial cell walls. Cell wall peroxidases were then isolated from epidermal strips and further characterized. The possible presence of a H₂O₂-generating system in the epidermis of mung bean hypocotyls was also investigated. When whole segments were processed for electron microscopy, H₂O₂ could be detected cytochemically in the cell walls with the CeCl₃ technique. A positive reaction was obtained in the same location when specimens were incubated in a 3-3′-diaminobenzidine medium for peroxidases in which H₂O₂ was replaced by its possible precursors (NADH or NAD + malate). However, isolated epidermal cell walls could not generate H₂O₂ at the expense of NADH although they were able to oxidize the reduced nicotinamide-adenine-dinucleotide. The possible relationships between peroxidase activities, H₂O₂, and Ca²⁺ ions are discussed with respect to their involvement in the cell wall stiffening process.