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 ethylenetreated
styles and petals corresponded with increases in
ethylene biosynthesis, with increases in ACS mRNA
abundance detected at stage 1 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