Role of ABA in triggering ethylene production in the gynoecium of senescing carnation flowers: Changes in ABA content and expression of genes for ABA biosynthesis and action

In senescing carnation (Dianthus caryophyllus L.) flowers, ethylene production begins in the gynoecium, and the resulting ethylene acts on petals, inducing autocatalytic ethylene production. We investigated the role of abscisic acid (ABA) in ethylene production in the gynoecium of flowers. First, cDNAs of major genes involved in ABA biosynthesis and signaling were cloned from carnation flower tissues. Then, changes in ABA content and gene expression of ABA biosynthesis and signaling in the ovary were examined using three cultivars, 'Light Pink Barbara (LPB)' and 'Excerea', whose cut flowers produce ethylene during senescence and have an ordinary vaselife of about one week, and 'Miracle Rouge', whose cut flowers produce no detectable ethylene during senescence and have a vase-life of about three weeks. ABA content in the ovary was 530-710 pmol·g^-1 fresh weight (FW) from Os 2 (early opening stage) to Os 6 (end of opening stage) in 'LPB', and at 200-380 pmol·g^-1 FW in 'Excerea' at the same stages; but 930 pmol·g^-1 FW at Ss 1 (early senescence stage). The ABA content remained at 70- 160 pmol·g^-1 FW in 'Miracle Rouge'. The changes in ABA content were in parallel with the transcript levels of DcNCED1 (carnation gene for 9-cis-epoxycarotenoid dioxygenase). DcPYR1 (ABA receptor gene) transcript was 0.004-0.007 relative expression level (r.e.l.) in 'LPB' ovary at Os 1-Os 3, and 0.028 r.e.l. at Ss 1 (beginning of senescence stage). In 'Excerea' ovary, DcPYR1 transcript was 0.025-0.037 r.e.l. during flower opening and higher at Ss 1. By contrast, DcPYR1 transcript remained at 0.002-0.006 r.e.l. in 'Miracle Rouge' ovary during flower opening and senescence. The transcripts of DcACS1, the key gene for ethylene biosynthesis, were detected at Ss 1 in 'LPB', and at Ss 2 in 'Excerea', but not in 'Miracle Rouge' throughout flower opening and senescence stages. These findings suggest that ABA plays a causal role in inducing the expression of the DcACS1 gene in the gynoecium, leading to ethylene biosynthesis, and that both the ABA content and DcPYR1 expression must be above putative threshold levels for ABA to exert its action.