Mechanism of Naphthaleneacetic Acid Conjugation: No Effect of Ethylene ¹ Free

Formation of naphthaleneacetic acid-glucose (NAGLu) in detached leaves, floating on α-naphthaleneacetic acid-1-¹⁴C (NAA, 0.05 microcurie per milliliter, 3.1 μm)-buffer solution (phosphate-citrate, pH 4.2) began immediately while there was a 2- to 4-hour lag before NAA-asparatate (NAAsp) could be detected. Subsequent increase in the NAAsp conjugate reflected a decrease in free NAA to 1 to 2% of the total radioactivity taken up. Pretreatment with 31 μm¹²C-NAA for 18 hours doubled NAAsp formation after transfer for 4 hours to ¹⁴C-NAA. Pretreatment with ethylene, as ethephon (up to 400 milligrams per liter) or ethylene gas (10 microliters per liter), did not induce NAAsp formation. In the presence of NAA, ethylene had no effect on NAA conjugation. Similarly, CO₂ (5%) did not modify the formation of the conjugates. Rhizobitoxine (1.87 μm) inhibited NAA-induced ethylene production but did not prevent NAA-induced formation of NAAsp. We concluded that the conjugation of NAA with aspartic acid is not mediated by ethylene.