Plant Molecular Biology 34: 45–55, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Expression of ethylene biosynthetic genes in Actinidia chinensis fruit
David J. Whittaker
, Garth S. Smith
and Richard C. Gardner
Centre for Gene Technology, School of Biological Sciences, University of Auckland, Private Bag 92019,
Auckland, New Zealand (
author for correspondence);
Horticulture and Food Research Institute of New
Zealand, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand
Received 9 July 1996; accepted in revised form 17 January 1997
Key words: ACC oxidase, ACC synthase, ethylene regulation, fruit ripening, kiwifruit, SAM synthetase
The fruit of Actinidia chinensis, a diploid relative of kiwifruit, showed an increased rate of ripening in response to
theapplicationofexogenousethylene.Moreover,late in ripeningthefruitproducedaburstof ethylenebiosynthesis.
Thusripeningis climacteric, and there is acleartemporalseparationof ethylenesensitivityandethyleneproduction.
RNase protection assays were used to monitor transcript levels of ethylene biosynthetic genes during fruit devel-
opment and ethylene-induced ripening. The application of exogenous ethylene correlated with increased transcript
levels for three different S-adenosyl-L-methionine (SAM) synthetase genes and for the 1-aminocyclopropane-1-
carboxylate (ACC) oxidase gene family. Transcription of an ACC synthase gene was not affected by exogenous
ethylene. However, ACC synthase transcript levels increased during subsequent ethylene production by the fruit,
consistent with this being the control step for the onset of climacteric ethylene production. ACC oxidase transcripts
increased signiﬁcantly both prior to and during climacteric ethylene production, while only one of the three SAM
synthetasetranscripts was inducedduringthelate ethyleneburst. We proposethat the regulation of SAM synthetase
transcripts by ethylene may occur as part of the methionine salvage pathway.
The simple gas ethylene is an endogenous regulator of
a variety of stress responses and developmental pro-
cesses . Ethylene biosynthesis is strictly regulated,
ingmechanicaltrauma, pathogeninfection, auxinsand
developmental factors in senescing ﬂowers and ripen-
ing fruit . The route of ethylene biosynthesis was
elucidated by Adams and Yang , and involves three
ethylene. In this path-
way, the conversion of SAM to ACC, catalysed by
ACC synthase (EC 18.104.22.168), is generally regarded as
the rate-limiting step . The enzyme ACC oxidase
converts ACC to ethylene, CO
and cyanide. Though
ACC oxidase is expressed constitutively in most tis-
sues, its synthesis increases during ripening in tomato
. SAM synthetase (EC 22.214.171.124) catalyses the bio-
synthesis of SAM, the immediate precursor of ACC.
In addition to its role in ethylene synthesis, SAM is the
major methyl group donor in numerous transmethyla-
tionreactions thattakeplacein the cell, andaprecursor
in the synthesis of polyamines.
genes that have similar expression patterns [28, 29].
Tomato has at least four SAM synthetase genes, and
three of these havebeen isolatedand shown to respond
differentially to salt stress in seedlings . ACC syn-
thase is encoded by multigene families in all species
examined, and differential regulation of the individual
genes has been reported [9, 27]. Multiple ACC oxi-
dase genes have been isolated from both tomato and
petunia, and these also are differentially regulated [3,
It is now well established that ethylene promotes
many aspects of ripening in climacteric fruit. The
molecular basis of fruit ripening has been most widely
studied in tomato (Lycopersicon esculentum). Mutants
blocked in various aspects of fruit ripening are avail-
able  and numerous ripening-related genes have
GR: 201001890, Pips nr. 133229 BIO2KAP
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