The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporaDly with petal-inroDling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or amino- is disruption of membrane integrity and loss of intracellular compartmentation. Kende et al. (3,28) have noted a strong correlation between membrane leakiness and phospholipid breakdown in senescing flowers. Moreover, treatment of Tradescantia with ethylene accelerates the onset of membrane leakiness and phospholipid deterioration in petals, but the ethylene effect is dependent upon synthesis of new protein (28). Borochov et al. (6,7) have reported that the microviscosity of plasma membranes from rose petals rises with advancing senescence in a manner that correlates with an increase in sterol:phospholipid ratio reflecting phospholipid breakdown.Senescing carnation flowers exhibit a climacteric-like rise in ethylene production (5,17,20). In addition, exposure of carnation flowers to exogenous ethylene induces inrolling of the petals and results in increased ethylene synthesis (10, 24, 26). In the present study, we have used cut carnation flowers to examine the ability of ethylene to induce chemical and physical changes in microsomal membrane lipids of senescing petals. MATERIALS AND METHODSPlant Material. Carnation flowers (Dianthus caryophyllus L. cv. White Sim) were grown in raised beds in a greenhouse according to established culturing procedures. Mature flowers were cut at the commercial stage of development (fully open with a yellowish tinted center) and either used directly for membrane isolation or trimmed to an 8 cm stem length and placed individually in 20-ml vials containing either deionized water or test solutions. Flowers held in water or test solutions were maintained at 22°C, and the levels of water or test solutions were adjusted as necessary to 1 cm below the calyx.Treatments. For treatment with ethylene, flowers were placed in deionized H20 in specially constructed Plexiglas chambers (135 L capacity) equipped with an internal fan to promote circulation, two ports for gas flow, and a removeable front panel. Exposure to ethylene was achieved by injecting ethylene into the chambers to a final concentration of 1 ,pl/l. Throughout the exposure, the chambers were connected to an air stream containing 1 ,ld/l ethylene that was flowing at 20 ml/min. Chambers containing control flowers were flushed at the same rate with air that had been rendered ethylene-free by passage through potassium permanganate coated with aluminum silicate (Purafil, Chamblee, GA). Ethylene treatments were terminated by removing the flowers from the chambers t...
The role of abscisic acid and ethylene in the senescence of rose petals cv. Golden-Wave was examined. A rise in ethylene evolution, followed by an increase in the level of abscisic acid was observed. The presence of abscisic acid in rose petals was established, using different chromatography systems, several bioassays, and immunoassay. External application of ethylene accelerated senescence and induced a rise in endogenous abscisic acid-like activity. Application of abscisic acid promoted senescence, but suppressed ethylene production. The data suggest that the participation of these two hormones in the control of senescence is via the same pathway. The possibility of interrelationship between abscisic acid and ethylene was tested and experimental evidence in favor of this hypothesis is presented. It was suggested that ethylene affects senescence in rose petals by inducing an increase in abscisic acid activity, which in turn may control ethylene evolution, via a feedback mechanism.
Carnation (Dianthus caryophyllus) flowers were exposed to 2^i/l ethylene and examined at intervals to determine the time course of wilting, decrease in water uptake, and increase in ionic leakage in response to ethylene. A rapid decrease in water uptake was observed about 4 hours after initiating treatment with ethylene. This was followed by wilting (in-rolling of petals) about 2 hours later. Carbon dioxide inhibited the decline in water uptake and wilting and this is typical of most ethylene-induced responses. Ethylene did not affect closure of stomates. Ethylene enhanced ionic leakage, as measured by efflux of 36CI from the vacuole. This was judged to coincide with the decrease in water uptake. Gassing flowers with propylene initiated autocatalytic ethylene production within 2.4 hours. Since the increase in ethylene production by carnations preceded the increase in ionic leakage and the decline in water uptake by several hours, it is apparent that the change in ionic leakage does not lead to the initial increase in ethylene production as reported (Hanson and Kende 1975 Plant Physiol 55:663-669) in morning glory but may explain the autocatalytic phase of ethylene production.The association of ethylene with senescence of flowers is widely recognized and carnation flowers have been thoroughly examined in this respect (13). As the cut flower approaches senescence, a dramatic rise in the rate of ethylene production occurs followed soon after by wilting of the petals. Senescence can be hastened by as little as 30 nl/l of ethylene (2, 15). The events taking place between the rise in ethylene production, or exposure to ethylene, and the development of visual symptoms remain obscure. Lieberman et al. (11) over-all length, and placed individually in 20-ml vials. Flowers were obtained from a local grower and experiments were begun on the day of harvest. Four flowers in a 10-liter desiccator with a CO2 scrubber (NaOH solution) comprised a treatment. Flowers 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 ml/min for the remainder of the experiment. Flowers were observed at 1-hr intervals to determine the onset of wilting symptoms as judged by in-rolling of petals.Effect of Ethylene on Rate of Water Uptake. Cut flowers were fitted into a specially designed glass sphere in which the flower bud was maintained in the desired gas atmosphere while the stem was connected to a potometer (5) and water uptake was measured at 30-min intervals. The flowers were ventilated continuously with 2 ,ul/l ethylene in dry air or with ethylene-free at a flow rate of 40 ml/min.Effect of Ethylene on Stomatal Aperture of Carnation Sepals. Flowers were cut to 10 cm over-all length and treated with ethylenie in desiccators as described above. Flowers were removed at 3-hr intervals from each of four desiccators and the sepals were excised, frozen in liquid N2, and freeze-dried. Sections (4 x 4 mm) were sputter-coated with gold and the surface was observed ...
Mung bean cuttings were dipped in solutions of wild type and mutant forms of the plant growth-promoting rhizobacterium Pseudomonas putida GR12-2 and then incubated for several days until roots formed. The bacteria P. putida GR12-2 and P. putida GR12-2/aux1 mutant do not produce detectable levels of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, whereas P. putida GR12-2/acd36 is an ACC deaminase minus mutant. All bacteria produce the phytohormone indole-3-acetic acid (IAA), and P. putida GR12-2/aux1 overproduces it. Treatment of cuttings with the above-mentioned bacteria affected the rates of ethylene production in the cuttings in a way that can be explained by the combined effects of the activity of ACC deaminase localized in the bacteria and bacterial produced IAA. P. putida GR12-2 and P. putida GR12-2/acd36-treated cuttings had a significantly higher number of roots compared with cuttings rooted in water. In addition, the wild type influenced the development of longer roots. P. putida GR12-2/aux1 stimulated the highest rates of ethylene production but did not influence the number of roots. These results are consistent with the notion that ethylene is involved in the initiation and elongation of adventitious roots in mung bean cuttings.
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