Ethylene Biosynthesis - Fruit Ripening: Physiology, Signalling and Genomics - page 186

10 Ethylene Biosynthesis

Donald Grierson*
Laboratory of Fruit Quality Biology/The State Agriculture Ministry
Laboratory of Horticultural Plant Growth, Development and Quality
Improvement, Zhejiang University, Hangzhou, China; Plant and Crop
Sciences Division, School of Biosciences, University of Nottingham,
Loughborough, UK

in ethylene production regulated so
precisely in different situations? As we
shall see, there are two key enzymes
required for ethylene synthesis (ACC
synthase and ACC oxidase) and there is a
range of mechanisms controlling their
transcriptional and post-transcriptional
regulation.
Classic research by Mapson, Lieberman
and colleagues (Lieberman et al. , 1965,
1966; reviewed by Lieberman, 1979)
showed that the amino acid methionine
was a precursor of ethylene in plants, and
that the CH 2 groups of methionine form
carbons 1 and 2 of ethylene (Fig. 10.1).
The three essential reactions are:
activation of L -methionine (Met) to form
S -adenosylmethionine (AdoMet); conver-
sion of AdoMet to 1-aminocyclopropane-1-
carboxylic acid (ACC), a non-protein
amino acid; and conversion of ACC to
ethylene, as follows.
The fi rst reaction is catalysed by
S -adenosylmethionine synthetase (EC
2.45.1.6), which requires Mg 2+ and K + (or
another monovalent cation):

10.1 Introduction

Research during the fi rst few decades of
the 20th century showed that hydrocarbon
gases in the environment infl uence plant
growth, development and fruit ripening.
Once it was realized that ethylene was the
key molecule in this process, and that
plants produce it themselves, it was
recognized as a bona fi de hormone. This
stimulated interest in determining the
pathway of ethylene biosynthesis and led,
ultimately, to the discovery of the
enzymes, genes and regulatory factors that
control ethylene production and action at
different stages in the life cycle. All plants
produce ethylene, but increased ethylene
production occurs at many stages of
development, particularly in response to
developmental signals (e.g. fl ower develop-
ment and sex determination, abscission,
fruit ripening, leaf senescence), hormones
(e.g. auxin, cytokinin, ethylene) and
environmental infl uences (e.g. infection,
wounding, chilling drought, UV light,
oxidative stresses such as SO 2 and O 3 )
(Abeles et al. , 1992). This raises the
question: how are the observed increases Met + ATP o AdoMet + PP i + P i (1)