Ethylene production and enhanced transcription of an ethylene receptor gene, ERS1, in Delphinium during abscission of florets

Delphinium spp. L florets are known to undergo severe senescence a few days after harvesting as cut flowers. Using a cDNA library made from mRNA extracted from Delphinium florets 4 d harvesting, we isolated and identified cDNAs encoding ethylene response sensor (ERS)-type ethylene receptors, which contained an open reading frame of 1821 bp encoding a polypeptide of 606 amino acid residues. These were classified into two types with minor differences; Dl-ERS1 (Delphinium little-strain ERS1) type-1 (DDBJ/EMBL/GenBank AB055429) and Dl-ERS1 type-2 (DDBJ/EMBL/GenBank AB055430). We were able to identify only ERS1 in Delphinium using the cDNA library screening, 3′ RACE (DDBJ/EMBL/GenBank AB106892, AB106893), and genomic PCR (DDBJ/EMBL/GenBank AB106891). Northern blot analysis showed that the transcription of ERS1 gene doubled between 0 and 3 d after harvesting, increased sharply to a maximum at 4 d, and then declined, while abscission of florets increased slowly until 3 d, and then increased rapidly at 4–5 d after cutting. Ethylene evolution increased until 4 d, and then decreased at 6 d after cutting. From these results, we postulate that abscission of florets in Delphinium is caused by the elevated levels of ethylene receptor, ERS1, and that these will be influenced by endogenous ethylene generated after cutting the stem.