1-aminocyclopropane-1-carboxylate oxidase from embryonic axes of germinating chick-pea (Cicer arietinum L.) seeds: cellular immunolocalization and alterations in its expression by indole-3-acetic acid, abscisic acid and spermine

A recombinant protein (approximately 38 kDa by SDS/PAGE), induced by expres sion in Escherichia coli of a cDNA encoding a 1-aminocyclopropane-1-carboxy late oxidase (ACO) isolated from embryonic axes of Cicer arietinum, was rec ognized by an antibody raised against an apple ACO. A monoclonal antibody, obtained from recombinant ACO of chick-peas, was used for immunolocalizatio n experiments in the embryonic axes of chick-pea seeds. The results indicat e that most of the ACO was present in the apoplast of the cell wall. No evi dence of this protein in the vacuole was detected. During germination of C. arietinum seeds, the production of ethylene was induced in the embryonic a xis; its highest value was reached when radicle emergence occurred. At this moment there was an accumulation of 1-aminocyclopropane-1-carboxylate (ACC ), transcription of ACO mRNA, as well as maximal ACO activity. In the postg erminative period the activity of the last step of ethylene biosynthesis de creased. This decrease was eliminated by indole-3-acetic acid (IAA), which caused significant transcription of ACO mRNA. It is suggested that gene exp ression of ACO may be induced by auxins and spermine (Spm) and inhibited by abscisic acid (ABA).