Repressed ethylene production in the gynoecium of long-lasting flowers of the carnation 'White Candle': role of the gynoecium in carnation flower senescence

Ethylene production and expression of ethylene biosynthetic genes was investigated in senescing flowers of carnation (Dianthus caryophyllus L.) cultivars 'White Candle (WC)' and 'Light Pink Barbara (LPB)', with long and short vase-lives, respectively. Ethylene production from the gynoecium and petals of senescing 'WC' flowers was below the limit of detection, in agreement with the repressed ethylene production from the whole flowers. However, exogenous ethylene treatment caused the accumulation of transcripts for DC-ACS1 and DC-ACO1 genes in both the gynoecium and petals, resulting in ethylene production from the flowers. Moreover, application of ABA or IAA, which are known to exhibit their action through the induction of ethylene synthesis in the gynoecium, to 'WC' flowers from their cut stem-end induced ethylene production and wilting in the flowers. These findings suggested that, in 'WC' flowers the mechanism of ethylene biosynthesis, i.e. the induction of expression of genes for ethylene biosynthesis and the action of resulting enzymes, was not defective, but that its function was repressed during natural senescence. Transcripts of DC-ACO1, DC-ACS3, and DC-ACS1 were present in the gynoecium of senescing 'LPB' flowers. In the gynoecium of senescing 'WC' flowers, however, the DC-ACO1 transcript was present, but the DC-ACS1 transcript was absent and the DC-ACS3 transcript was detected only in a small amount; the latter two were associated with the low rate of ethylene production in the gynoecium of 'WC' flowers. These findings indicated that the repressed ethylene production in 'WC' flowers during natural senescence is caused by the repressed ethylene production in the gynoecium, giving further support for the role of the gynoecium in regulating petal senescence in carnation flowers.