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Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These (15) during dark-induced senescence of detached leaves. Also, polyamines inhibit development of RNase and protease activity in barley leaf discs (15). The mechanism by which polyamines exert these effects is unknown. These effects, however, are the opposite of those caused by the plant growth regulator, ethylene, which promotes senescence of many plant tissues (8).We investigated the effect of polyamines on ethylene biosynthesis, partly because polyamines and ethylene derive from the same precursor, S-adenosylmethionine (1, 2, 16), and because of the possibility that polyamines regulate plant metabolism by influencing the biosynthesis of ethylene.

Application of exogenous ethylene, irrespective of the method of application, caused intensification of mesocarp discoloration in avocado fruit (Persea americana Mill.) during cold storage of all cultivars tested. 'Ettinger' fruit treated with Ethrel (2-chloroethyl phosphonic acid) prior to packing and storage developed severe chilling injury (CI) symptoms, expressed as mesocarp discoloration after 3 weeks at 5°C. 'Fuerte' fruit treated with ethylene gas (100 ml l − 1 ) for 24 h at 20°C prior to storage at 5°C exhibited mesocarp discoloration, which increased dramatically during shelf life at 20°C. 'Fuerte' fruit treated in cold storage with a continuous low ethylene dose (4 ml l − 1 ) developed severe browning in the fruit pulp after 3 weeks at 5°C. 'Hass' fruit treated with 50 ml l − 1 ethylene, for 12, 24 or 48 h at 5°C showed a gradual increase in mesocarp discoloration after 3 weeks in cold storage plus shelf life; the 48 h ethylene-treated fruit exhibited the most severe pulp browning. Use of absorbent sachets that removed ethylene from modified atmosphere (MA) packaging reduced mesocarp discoloration and decay development in 'Hass' fruit after 5 weeks storage at 5°C. Application of 1-methylcyclopropene (1-MCP), reduced mesocarp discoloration, decay development and polyphenol oxidase activity, whereas this enzyme activity was induced in ethylene-treated fruits that were cold stored for 4 weeks.

Ethylene and supraoptimal levels of 2,4-dichlorophenoxyacetic acid inhibit the growth of the apical hook region of etiolated Pisum sativum (var. Alaska) seedlings by stopping almost all cell divisions. Cells are prevented from entering prophase. The hormones also retard cell division in intact root tips and completely stop the process in lateral buds. The latter inhibition is reversed partially by benzyl adenine. In root tips and the stem plumular and subhook regions, ethylene inhibits DNA synthesis. The magnitude of this inhibition is correlated with the degree of repression of cell division in meristematic tissue, suggesting that the effect on cell division results from a lack of DNA synthesis. Ethylene inhibits cell division withinm a few hours with a dose-response curve similar to that for most other actions of the gas. Experiments with seedlings grown under hypobaric conditions suggest that the gas naturally controls plumular expansion and cell division in the apical region.Growth of etiolated pea seedlings (38) and many other plants is suppressed by ethylene at least in part because the gas slows the rate of cellular expansion and causes roots and shoots to expand isodiametrically rather than longitudinally (4,(8)(9)(10)(11). In pea seedlings several processes dependent upon cell division are also inhibited by ethylene; for example, primary root elongation and lateral root formation (10, 11), lateral bud development (7), and expansion of the plumular leaf (18,19). Therefore, the effect of the gas on cellular division and DNA synthesis was investigated to determine whether these processes also might be involved in ethyleneinduced growth inhibition. Applied ethylene and auxin generally affect the growth of pea seedlings in a similar manner because auxin induces ethylene production (1,4,9,23,24,32 complete darkness at 23 C and 80% relative humidity. Unless otherwise indicated, 7-day-old plants with third internodes, approximately 1.5 cm long, were selected for experiments on plumular, stem, or bud growth, while 3-day-old seedlings with primary roots, 1 to 2 cm long, were used for studies on root growth. Pots of seedlings also were grown under hypobaric conditions by placing them in a 10-liter desiccator which was evacuated continuously at approximately 0.5 standard cubic foot per hr with a vented exhaust oil-seal pump. The pressure within the desiccator was maintained at 120 mm Hg by continuously admitting pure 02 to the desiccator through a Matheson No. 49 regulator (5). The incoming 02 was saturated at the reduced pressure by passing it through water.Growth Measurements. All tissue was handled under dim green light. A 5-mm stem region was demarcated with two ink spots just below the hook; this is referred to as the subhook region, and the region above it as the hook region. Groups of potted plants were either gassed with ethylene in air tight chambers, sprayed with 2,4-D, treated with a combination of the two hormones or irrigated with 2, 4-D solution. The chambers were aerated for several minutes e...

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