ACC Oxidase Expression and Leaf Ontogeny in White Clover

Abstract

During leaf ontogeny in white clover (Trifolium repens L.), significant production of ethylene occurs at the apex and from newly initiated leaves, and then again from senescent leaf tissue. A combination of RT-PCR and 3′- RACE, and Southern analysis has been used to identify three distinct ACC oxidase genes (designated TRACO1, TRACO2 and TRACO3) from leaf tissue of white clover. TRACO1 is expressed specifically in the apex, TRACO2 is expressed in the apex, and in developing and mature green leaves, with maximum expression in developing leaf tissue, and TRACO3 is expressed in senescent leaf tissue. Using protein purification techniques, three isoforms of ACC oxidase have been identified, one in mature green tissue (designated MG1) and two in senescent tissue (designated Sel, SeII). Some biochemical properties of each isoform are described.