Ethylene production and responses to exogenous ethylene in senescing petals of Chrysanthemum morifolium RAM cv Unsei

Senescence of chrysanthemum (Chrysanthemum morifolium RAM cv. Unsei) petals was associated with a marked deterioration of the plasma membrane and loss of water. The rates of ethylene synthesis declined after full bloom, and became non-detectable by the time the first symptoms of senescence were apparent. The drop in ethylene production correlated with a reciprocal increase in 1-aminocyclopropane-1-carboxylic acid (ACC) content. At full bloom, pre-treatment of petals with 1 mM ACC increased their rates of ethylene production several fold, but the capacity to convert exogenous ACC into ethylene decline thereafter. Inhibitors of ethylene synthesis (i.e. aminoxyacetic acid) or ethylene action (i.e. silver thiosulfate) had no effect on senescence, implying that the minute amounts of ethylene synthesized by petals are below the threshold to cause any acceleration of this process. However, petal senescence was significantly accelerated by a 24 h treatment with 3 ppm of ethylene at full bloom, or by continuous treatment with ethephon and ACC at concentrations that produce a significant increase of ethylene synthesis. Thus, our results show that petal senescence in some varieties of chrysanthemum is sensitive to exogenous ethylene, and that the extended vase life that is characteristic of these flowers may be due to, their low rates of ethylene synthesis. (C) 1997 Elsevier Science Ireland Ltd.