Plant Physiol . ( 1977 ) 60 , 203-206 ' 4 C 2 H 4 : Its Incorporation and Oxidation to 04 C 02 by Cut

Cut carnations (Dianthus caryophyllus L. cv. 'Improved White Sim') were exposed to utra high purity 1C2Ei (20 pU11) during flower opening and senescence to study its incorporation and metabolism. During treatment precautions were taken to exdude inhibitory volatiles from nibber serum stoppers which were identified as CS2 and COS. As with the pea seedling (Nature 1975, 255:144-147), cut carations incorporated 14C2H4 into ethanol-soluble tisse metabolites and oxidized the hormone to 14CO2. Oxidation increased from 0.5 to 3 dpm -mg dry wt-1 * 6 hr-1 during the period of flower opening and early petal wilt. As severe petal wilt set in, and the ovary increasd in size and dry weight, oxidation increased to a peak of nearly 29 dpm * mg dry wt-1 * 6 hr-1. Concomitant with this peak was a similar ise in the rate of 14C211 incorporation into the petals, pedunde, bracts, and sepals. Much higher rates of incorporation were found for the reproductive and receptade tissues. Incorporation into these tissues steadily inceased during flower opening reaching a peak of over 160 dpm mg dry wt-' * 6 hr-' just before ful bloom. This peak preceded a peak of endogenons ethylene production while the 14C2H4 oxidation pea foDlowed it. Substantial evidence now exists for the presence of an active ethylene metabolic system in intact pea seedlings (3, 4, 11) and a preliminary report suggests that a similar but less active system also exists in cotton and bean abscission explants (6). Two sequential purifications of the 14C2H4 by GC2 (3, 5) combined with the use of specific 14C2H4 trapping procedures (3) have eliminated the possibility that a labeled impurity might account for these results. Moreover, aseptic techniques combined with stringent tests for microbial contamination (3, 4) have further eliminated any possible involvement of microorganisms. In pea, this system results in the permanent incorporation of label from 14C2H4 into various ethanol-soluble tissue metabolites (11) and also in the oxidation of 14C2H4 to 14CO2 (3, 4, 11). Both of these components, oxidation and incorporation, have been partially characterized (4) and data are available on the effects of light; plant hormones; heat and homogenization; seedling fractionation; and 02, C02, and 14C2H4 concentration on the rate of 14C2H4 tissue incorporation and oxidation. The present study was undertaken to determine whether or not a similar ethylene incorporation and oxidation system may also be present in other ethylene-responsive tissues. Cut carnation flowers were examined during senescence in this study since 1 Contribution No. 2472 from Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours & Co., Wilmington, Delaware 19898. 2Abbreviation: GC: gas chromatography. they produce ethylene at substantial rates during senescence (10, 13, 15, 19, 21) and are highly responsive to the gas (2, 9, 10, 12-18, 20-25), providing circumstantial evidence that the gas is a natural accelerator of senescence in these flowers. In the present study data are presented indicating that cut carnations, like pea seedlings (3, 4, 11), also incorporate "4C2H4 and oxidize it to "4CO2. A preliminary report of this work has been published (6). MATERIALS AND METHODS Plant Material. Carnations (Dianthus caryophyllus L. cv. 'Improved White Sim') were obtained from a local nursery. Seventy-two flowers in the tight bud stage were cut 50 cm below the bud at 8 AM the day before 14C2H4 treatment (day 0, Fig. 1). The flowers were immediately transported to the laboratory where the stems were recut under water to a length of 25 cm, placed in beakers containing distilled H20, and maintained until needed under laboratory conditions. The following morning, (day 1, Fig. 1), five flowers were picked at random, the peduncle cut under water to a length of 5 mm, and each flower placed in a separate container (Fig. 2). On each succeeding morning of the experiment, additional flowers were selected at random as before for 14C2H4 treatment. 14C2H4 Treatment and Gas Analyses: Carnations, with peduncles trimmed to 5 mm, and a hypodermic needle stuck through the tip of the peduncle for weight, were enclosed in the apparatus shown in Figure 2. The glass container consisted of the modified, inverted cylindrical weighing bottle (70 x 33 mm) with a 71/15-mm ground glass joint. The lid of the weighing bottle formed the base of the chamber and was altered so that a test tube extended through its center 30 mm below and 10 mm above the container base. The stem of the flower was placed in the test tube which contained distilled H20, and 2 ml of 3 N NaOH were added to the bottom of the container around the protruding test tube to trap CO2. The bell-shaped container top, constructed from the base of the weighing bottle, was placed over the flower and sealed at the ground glass joint with stopcock grease. On top of the container was a stopcock fitted with a small rubber serum stopper. The purpose of the stopcock was to seal off the rubber serum stopper from the rest of the flask immediately after 14C2H4 injection. This was necessary since volatiles from rubber serum stoppers were previously found (3, 4) to inhibit 14C2H4 incorporation and oxidation to "4CO2. The active volatile components have recently been separated by GC isolated, and identified by mass spectroscopy. They are carbon disulfide, CS2, and carbonyl sulfide, COS (unpublished data, Beyer). During each of the 12 enclosure periods, a single carnation was sealed in each of five separate containers of about 250 ml (Fig. 2) and sufficient ultrapure 14C2H4 (3, 5) with a specific radioactivity of 22 mCi/mmol was injected into three of the 203 www.plantphysiol. org on April 29, 2019 Published by Downloaded from Copyright © 1977 American Society of Plant Biologists. All rights reserved. Plant Physiol. Vol. 60, 1977 FIG. 1. General appearance of carnation flowers at selected stages showing the progression of flower opening and rapid senescence. Numbers on bottles (0, 3, 6, 7, 8, and 9) are days with day 0 indicating the stage at harvest which was 1 day before the beginning of the experiment. Stems were cut to the length shown for photographic purposes. lation-counted in Aquasol (New England Nuclear). The NaOH from each container was removed and 1.5 ml were placed in a scintillation vial and dried under vacuum to remove H2O and dissolved '4C2H4. Four ml of H20 were then added and the sample liquid-scintillation counted as above. All data were corrected for counting efficiency and for sample quenching by the internal standard method using 14C-hexadecane. During peaks of ethylene incorporation and oxidation the radioactivity counted/ liquid scintillation vial exceeded several thousand dpm.