The site of 1‐aminocyclopropane‐1‐carboxylic acid synthesis in senescing carnation petals

To study the cause of the uneven production of ethylene by upper and basal portions of detached petals of carnation (Dianthus caryophyllus L. cv. White Sim), the petals were divided and exposed to ethylene (30 μl 1‐1 for 16 h). The treatment induced rapid wilting and autocatalytic ethylene production in the basal portion similar to that induced in entire petals. In contrast to the response in entire petals and the basal portions, the upper portions responded to ethylene by delayed wilting and much lower ethylene production. Aminocyclopropane carboxylic acid (ACC)‐synthase activity in the basal portion of the petals was 38 to 400 times that in the upper portion. In untreated detached petal pieces from senescing carnation flowers, ethylene production by the upper portion declined after 6 h while the basal portion was still producing ethylene at a steady rate 18 h later. Application of ACC to the upper portion of senescing petals increased their ethylene production. α‐Aminooxyacetic acid (0.5 mM), reduced the ethylene production of the senescing basal portion more than that of the upper portion. Endogenous ACC content in basal portions of senescing carnation petals was 3 to 4 times higher than in the upper parts. When detached senescing petals were divided immediately after detaching, the endogenous ACC levels in upper portions remained steady or declined during 24 h after division, while in the basal portions the ACC level rose steadily as in the intact petals. There was no change in the conjugated ACC in either portion after 24 h. Benzyladenine (BA) applied as a pretreatment to entire preclimacteric petals greatly reduced the development of ACC‐synthase activity of the basal portion, but had little effect on the activity in the upper portion of the petal. In both portions, however, BA effectively reduced the conversion of ACC to ethylene.