Analysis of the distribution of copper amine oxidase in cell walls of legume seedlings

Copper-containing amine oxidase (CuAO) has been proposed to play a role in H2O2 production in plant cell walls during cell development and in response to pathogen attack. We have compared the localisation of CuAO in pea (Pisum sativum L.), lentil (Lens culinaris M.) and chick pea (Cicer arietinum L.) grown under different light conditions, using both immuno- and histochemical techniques. The enzyme was detected by indirect immunofluorescence in the cell walls of parenchyma tissues of etiolated pea and lentil plants and was particularly abundant at intercellular spaces. Upon de-etiolation, CuAO largely disappeared from cortical cell walls except in the region of intercellular spaces. In the apical internode of light-grown seedlings, CuAO occurred mainly in cortical cell walls and, to some extent, in cell walls of xylem vessels. In both the elongation zone and mature regions of roots, CuAO was restricted to cortical cell walls and some cell junctions close to the meristem. Extensin epitopes co-localised to intercellular spaces of the cortex in de-etiolated pea, indicating that CuAO may have a role in cell wall strengthening at intercellular spaces. In chick pea, the localisation of the enzyme varied between different cultivars that have differing susceptibility to the fungus Ascochyta rabiei. In a susceptible cultivar Calia, immunogold labelling localised CuAO to cell walls of the cortex, as in lentil and pea, while in a resistant cultivar Sultano, it was most abundant in xylem vessels and, in light-grown plants, in the epidermis. These expression patterns are discussed with regard to the possible functions of amine oxidase in cell growth, cell differentiation and pathogen resistance.