Plant Molecular Biology 48: 351–359, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Expression of the ACC synthase and ACC oxidase coding genes after
self-pollination and incongruous pollination of tobacco pistils
A.M. Sanchez and C. Mariani
Department of Experimental Botany, Graduate school of Experimental Plant Sciences, Catholic University
of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, the Netherlands (
author for correspondence; e-mail
Received 12 January 2001; accepted in revised form 23 August 2001
Key words: ACC oxidase, ACC synthase, ethylene, incongruity, pollination
In tobacco, as in other species, ethylene is produced in response to pollination. Although tobacco is a self-
compatible species, it displays unilateral incongruity with other Nicotiana plants. Incongruous pollination also
results in ethylene production, but this production differs depending on the pollen used and is related to the extent
to which pollen tubes grow in the tobacco style. In the investigation reported here we followed the expression of the
ACC synthase- and ACC oxidase-coding genes upon pollination of tobacco pistils and compared self-pollination
with incongruous pollination. The pattern of expression of these genes also correlated with pollen-tube growth,
although wounding alone cannot explain the results obtained. We also examined the expression of these genes
upon pollination of immature tobacco pistils, in which different pollen tubes grew indistinctly inside the tobacco
style and reached the ovary at the same rate. In this situation no signiﬁcant differences in gene expression could be
observed between the different pollinations. Ethephon, a substance that produces ethylene, could, in some cases,
minimize the arrest of incongruous pollen tubes inside the style.
The gas ethylene is the simplest plant hormone pro-
duced either during plant development (e.g. during
fruit ripening, senescence, seed development, ﬂower-
ing) or as a response to environmental cues, wound-
ing, pathogenesis, and other stress-related responses
(Kieber and Ecker, 1993). In reproduction, ethylene
is involved in post-pollination responses that include
corolla and style senescence, changes in petal colour,
ovary enlargement and even ovule development in
some species (O’Neill, 1997).
The synthesis of ethylene begins with the pro-
duction of S-adenosylmethionine (SAM) from the
amino acid methionine. SAM is then converted to
1-aminocyclopropane-1-carboxylic acid (ACC), a re-
action catalysed by ACC synthase, which is further
oxidized to ethylene in the presence of ACC oxidase.
Both the ACC synthase- and the ACC oxidase-coding
genes belong to multigene families. Tobacco pistil-
speciﬁc ACC synthase and ACC oxidase cDNAs have
been isolated (Weterings, Pezzotti, Cornelissen and
Mariani, manuscript in preparation).
After production and release, ethylene is sensed
by the plant, and the signal is transduced in a phys-
iological response. The ethylene-signalling pathway
has been elucidated in Arabidopsis through the isola-
tion and characterization of several mutants deﬁcient
in the perception of ethylene or the response to it
(Johnson and Ecker, 1998). Homologues for the genes
cloned in Arabidopsis have also been identiﬁed in
other species, suggesting that similar pathways might
occur throughout the plant kingdom (Bleecker, 1999).
The model currently accepted for ethylene action pos-
tulates the existence of a phosphorylation cascade
that connects the ethylene membrane receptor (where
ethylene is sensed upon binding) to the action of dif-
ferent ethylene-related transcription factors that lead
to the phenotypes associated with exposure to ethylene
(Woeste and Kieber, 1998).