Ethylene responsiveness in carnation styles is associated with stigma receptivity

Sensitivity to ethylene increases as flowers mature, and this is associated with autocatalytic ethylene production that initiates petal senescence. The coordination of the senescence process within the flower requires interorgan communication. To determine if differential ethylene responsiveness among floral organs is involved in regulating senescence signaling, ethylene biosynthesis and the expression of ethylene biosynthetic genes were investigated in styles, ovaries, and petals from 6 stages of flowers following ethylene treatment. As flowers matured, all floral organs investigated became more responsive to ethylene. Ovaries were the first flower organ that had detectable increases in ethylene production following ethylene treatment. In stage 4 and 5 flowers, the highest levels of ethylene production were detected in petals, while styles had the highest ethylene production at stage 6. 1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) genes were induced by ethylene treatment, and transcript abundance of DCACS1, DCACS2 and DCACO1 increased in all floral organs as flowers matured. DCACS3, a pollinationresponsive ACS gene, did not show a significant increase in transcript levels following ethylene treatment except in styles. Patterns of gene expression in ethylene-treated styles and petals corresponded with increases in ethylene biosynthesis, with increases in ACS mRNA abundance detected at stage I or 2 in petals and at stages 4, 5, or 6 in styles. The largest increases in ethylene production and gene expression occurred in styles at stages 5 and 6 and corresponded to the stages at which the styles were first receptive to pollination. Reasons for differential ethylene sensitivity among the flower organs during development are discussed.