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 (Pisu m sativum L.), lentil (Lens culinaris M.) and chick pea (Cicer arietinum L. ) grown under different light conditions, using both immuno- and histochemi cal techniques. The enzyme was detected by indirect immunofluorescence in t he cell walls of parenchyma tissues of etiolated pea and lentil plants and was particularly abundant at intercellular spaces. Upon deetiolation, CuAO largely disappeared from cortical cell walls except in the region of interc ellular spaces. In the apical internode of light-grown seedlings, CuAO occu rred mainly in cortical cell walls and, to some extent, in cell walls of xy lem 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 cor tex in de-etiolated pea, indicating that CuAO may have a role in cell wall strengthening at intercellular spaces. In chick pea, the localisation of th e enzyme varied between different cultivars that have differing susceptibil ity to the fungus Ascochyta rabiei. In a susceptible cultivar Calia, immuno gold 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 patt erns are discussed with regard to the possible functions of amine oxidase i n cell growth, cell differentiation and pathogen resistance.