Plant Physiol. (1977) 59, 591-593 Regulation of Senescence in Carnation (Dianthus caryophyllus) by Ethylene MODE OF ACTION1 Received for publication April 9, 1976 and in revised form November 16, 1976 SHIMON MAYAK,2 YOASH VAADIA,3 AND DAVID R. DILLEY Department ofHorticulture, Michigan State University, East Lansing, Michigan 48824 ABSTRACT over-all length, and placed individually in 20-ml vials. Flowers Carnation (Dianthus caryophyllus) flowers were exposed to 2 ^i/l were obtained from a local grower and experiments were begun ethylene and examined at intervals to determine the time course of on the day of harvest. Four flowers in a 10-liter desiccator with a wilting, decrease in water uptake, and increase in ionic leakage in CO2 scrubber (NaOH solution) comprised a treatment. Flowers response to ethylene. A rapid decrease in water uptake was observed were exposed to ethylene at 21AI/I for 0, 3, 6, 9, or 12 hr, after which they were ventilated with ethylene-free air at a rate of 100 about 4 hours after initiating treatment with ethylene. This was followed were of 2 ml/min for the remainder of the experiment. Flowers by wilting (in-rolling petals) about hours later. Carbon dioxide observed at 1-hr intervals to determine the onset of wilting inhibited the decline in water uptake and wilting and this is typical of symptoms as judged by in-rolling of petals. most ethylene-induced responses. Ethylene did not affect closure of Effect of Ethylene on Rate of Water Uptake. Cut flowers stomates. Ethylene enhanced ionic leakage, as measured by efflux of 36CI a in which the from the vacuole. This was judged to coincide with the decrease in water were fitted into specially designed glass sphere uptake. Gassing flowers with propylene initiated autocatalytic ethylene flower bud was maintained in the desired gas atmosphere while the stem was connected to a potometer (5) and water uptake was production within 2.4 hours. Since the increase in ethylene production measured at 30-min intervals. The flowers were ventilated con- by carnations preceded the increase in ionic leakage and the decline in tinuously with 2 ,ul/l ethylene in dry air or with ethylene-free at a water uptake by several hours, it is apparent that the change in ionic flow rate of 40 ml/min. leakage does not lead to the initial increase in ethylene production as Effect of Ethylene on Stomatal Aperture of Carnation Sepals. reported (Hanson and Kende 1975 Plant Physiol 55:663-669) in morn- to 10 cm over-all and treated ing but may explain the autocatalytic phase ofethylene production. Flowers were cut length with glory ethylenie in desiccators as described above. Flowers were re- moved at 3-hr intervals from each of four desiccators and the sepals were excised, frozen in liquid N2, and freeze-dried. Sec- tions (4 x 4 mm) were sputter-coated with gold and the surface The association of ethylene with senescence of flowers is was observed with a scanning electron microscope to determine widely recognized and carnation flowers have been thoroughly degree of opening of the stomates. examined in this respect (13). As the cut flower approaches Effect of Propylene on Ethylene Production. Individual flow- senescence, a dramatic rise in the rate of ethylene production ers were fitted into 220-ml conical chambers equipped for aera- occurs followed soon after by wilting of the petals. Senescence tion and gas sampling. The chamber accommodated an open can be hastened by as little as 30 nl/l of ethylene (2, 15). The flower without exerting mechanical pressure on the petals and events taking place between the rise in ethylene production, or the protruding flower stem was immersed in deionized H20. The exposure to ethylene, and the development of visual symptoms funnel chamber was ventilated with ethylene-free air at a flow remain obscure. Lieberman et al. (11) have shown that ethylene rate of 40 ml/min. Ethylene production was monitored at 24-hr accelerates the loss of water from the carnation inflorescence, intervals for 1 day by alternately sealing and ventilating the and Nichols (13) demonstrated that a loss in fresh weight of chamber. On the 2nd day, 38 hr after the experiment was carnation flowers is correlated with the rise in ethylene produc- initiated, the chambers were closed and some of the flowers were tion. The influence of ethylene on physiological changes leading treated with propylene (260 ,ul/l) for 8 hr and ethylene produc- to the wilting phenomenon of carnations was investigated to tion was measured at 2-hr intervals. The chambers were then determine the sequence of certain events culminating in flower ventilated for 20 hr after which ethylene production was again senescence. monitored at 2-hr intervals as before. Ethylene determinations were made on a Varian 1700 gas chromatograph employing a MATERIALS AND METHODS flame ionization detector and an alumina column. Effect of Ethylene on Wilting. Carnation flowers Dianthus Effect of Ethylene on Ionic Fluxes. The change in efflux of caryophyllus, cv. Improved White Sim) were cut to about 10 cm ions in the petal tissue was determined in relation to the onset of wilting of carnation flowers preloaded with HwCl (about 4 x 105 The ion efflux procedure of Keck and I Michigan Agricultural Experiment Station Journal Article No. cpm/flower). Hodges (8) 7658. Supported in part by the Gillette Company. and Hanson and Kende (7) was used with slight modifications. 2 Present address: Faculty of Agriculture, The Hebrew University, Half of the flowers were gassed with ethylene at 2 ,ul/l while the Rehovot, Israel. others were ventilated with ethylene-free air. Flowers were re- 3 Present address: Ministry of Agriculture, The Volcani Center, Bet moved at 2-hr intervals for efflux measurements. Those which Dagan, Israel. received 8-hr exposure to ethylene exhibited wilting symptoms. 591 592 MAYAK, VAADIA, AND DILLEY Plant Physiol. Vol. 59, 1977 RESULTS AND DISCUSSION *-I Ethylene-induced Wilting. The first visual symptom of carna- o AIR tions treated with ethylene was an "in-rolling" or wilting of the . C2H4 2,/el/ petal margin as described by Nichols (13). Wilting was first °C2 H4 2seC/e+C024% observed at 6 hr for flowers receiving ethylene at 2 ,ul/1 and at 60 c 90 hr for those ventilated with air continuously. The number of 3: flowers exhibiting wilting increased with the duration of expo- 0 sure to ethylene. Nine- or 12-hr treatment with ethylene was It sufficient to cause most of the flowers to wilt in 2 days while less than a third of the flowers receiving 3- or 6-hr exposure dis- IL played the wilt symptom in this interval. This demonstrates the variability with respect to sensitivity to ethylene that exists IC within a given population of presumably uniform flowers. 48,70 I.w Water Uptake. The rate of water uptake declined sharply U. approximately 4 hr after gassing the inflorescence with 2 or 20 ~ 0 ,ul/l ethylene (Fig. 1) and stabilized at about 70% of the control value. Wilting was observed between 6 and 7 hr after ethylene w w 60 treatment. Flowers gassed with 0.2 ,ull ethylene showed a de- !i cline in water uptake beginning in 12 hr but these did not wilt. 4x Carbon dioxide inhibited the ethylene-induced decline in water I LA0 Water uptake was slightly lower in uptake and wilting (Fig. 2). ..f the presence of 4% CO2 which may be attributed to closure of 0 2 4 6 8 10 12 stomates on the flower sepals. The fact that CO2 negates the TIME (hrs) decline in water uptake induced by ethylene places this ethylene FIG. 2. Effect of ethylene (2 ,ul/l) with or without 4% CO2 on the response in the same category with a long list of other ethylene- rate of water uptake by carnation flowers. The flowers, excluding the induced responses found to be reversibly inhibited by CO2 (4). It stem, were ventilated with the gas mixtures at 20 C in light at 200 ft-c. W has long been recognized that CO2 delays wilting of carnations indicated time of initial wilting. (14). Scanning electron microscopy of the sepals did not reveal loaded with 36Cl and gassed with ethylene for 5.5 hr since it was differences in stomate opening, before the onset of wilting, established earlier that the decline in water uptake began 4 to 6 between ethylene-treated and untreated flowers. Thus, the de- hr after ethylene treatment followed by wilt symptoms about 2 cline in water uptake (Figs. 1 and 2) cannot be attributed to a hr later. The data, interpreted according to suggested guidelines direct effect of ethylene on stomate closure. (8, 12), indicates two phases of 36Cl efflux: a rapidly decreasing It is obvious but important to note that ethylene caused the initial phase attributed to Cl diffusing from a readily accessible decline in water uptake before the visual symptom of wilt. This is compartment which'may include the cell wall and some exchange indirect evidence that ethylene causes a change in water and through the plasmalemma, from which the rate of efflux is solute distribution within the cell perhaps because of a change in similar regardless of ethylene treatment; and a slow linear phase membrane permeability and hence a drop in turgor pressure attributed to release of Cl from the vacuole through the tono- accounting for the decline in water uptake (10). Direct evidence plast which occurs at a faster rate with flowers pretreated with supporting this hypothesis was obtained by ion efflux compart- ethylene. We conclude that this is due to an increase in tonoplast mentation analysis.