Plant Molecular Biology 39: 209–219, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
A multi-responsive gene encoding 1-aminocyclopropane-1-carboxylate
synthase (ACS6) in mature Arabidopsis leaves
Jeannette M. Arteca and Richard N. Arteca
Department of Horticulture, The Pennsylvania State University, University Park, PA 16802, USA (
Received 19 June 1998; accepted in revised form 11 August 1998
Key words: Arabidopsis, ACC synthase, ethylene, light, touch, wound
Physiological and biochemical studies have provided evidence that mechanical strain (touch)-induced modiﬁca-
tions in plant growth and development may be due to ethylene. In order to better understand the involvement of
ethylene in touch-induced responses, we identiﬁed and characterized an Arabidopsis cDNA (ACS6) encoding 1-
aminocyclopropane-1-carboxylic acid (ACC) synthase which is an important regulatory enzyme in the ethylene
biosynthetic pathway. Northern analysis showed that ACS6 was induced by touch in the leaves of 3-week old
light-grown plants within 5 min and reached maximum transcription at 15 min. ACC, which is the product of
ACC synthase and the immediate precursor to ethylene, exhibited a dramatic rise between 15 and 30 min after
touch stimulation. Experiments with multiple touch treatments showed that a saturation in gene expression was
obtained withone touch treatment and subsequent touch stimulationswere progressivelyless effectiveinpromoting
ACS6 expression. Additional characterization of ACS6 gene expression indicated that the gene is also induced by
wounding, and by treatment with LiCl, NaCl, CuCl
, auxin, cycloheximide (CHX), aminooxyacetic acid (AOA)
and ethylene. ACC levels were also increased in response to each of these treatments with the exception of CHX
and AOA which resulted in a decrease and no effect, respectively. Our results show that ACS6 is rapidly turned on
in response to touch which is followed by an increasein ACC which is the immediate precursor to ethylene,thereby
providingevidence that it is responsiblefor touch-inducibleethyleneproductionin light-grown Arabidopsisplants.
The identiﬁcation and characterization of ACS6 now provides us with a tool to better understand the involvement
of ethylene produced in response to external stimuli as well as during plant growth and development.
Plants are continually challenged throughout their life
cycle by a variety of adverse external stimuli, which
they cannot move away from in the same manner as
animals. The inability to move away from an adverse
environmenthas led to the evolutionof adaptivemech-
anisms which enable them to respond to a variety
of stress conditions rapidly with the proper defense.
These adaptations not only maximize their true poten-
Contribution No. 339, Department of Horticulture, The Pennsylva-
nia State University.
The nucleotide sequence data reported will appear in the Gen-
Bank Nucleotide Sequence Database under the accession number
tial, but in many cases act as a survival mechanism.
Mechanical forces (touch) can be caused by a variety
of natural factors  as well as agricultural and land-
scape practices . The ability of plants to respond to
touch was initially described by Darwin in 1880, and
since this time, there have been a number of reports
showing that plants are very responsive to touch in
a variety of experimental systems. The sensitivity of
plants to touch was initially thought to be due to an
artifact of plant hardening, adaptation to insectivory
or as an avoidance to herbivores . For a number
of years the effects of touch on plant growth and de-
velopment was left unnoticed because it was masked
or negatedby environmentalfactors. Researchers have
since been able to separate touch-induced responses