Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

Chapter 6
Ethylene Perception and
Gene Expression
Willis O. Owino and Hiroshi Ezura
6.1 Introduction
Fruits, vegetables, and flowers are economically important horticultural products liable
to postharvest deterioration and thus require appropriate postharvest handling techniques
to lengthen their shelf life while maintaining quality. An understanding of the key control
points of the physiological processes preceding senescence is necessary in developing useful
strategies for delaying postharvest deterioration in these plant products.
The phytohormone ethylene is known to regulate multiple physiological and developmental
processes in plants, such as leaf and flower senescence, fruit ripening, organ
abscission, and growth transition from vegetative phase to reproductive phase, and is also
involved in the reactions of plants to abiotic and biotic stresses (Abeles et al., 1992; Ogawara
et al., 2003; Guo and Ecker, 2004; Chen et al., 2005). Ethylene perception is a key event during
such physiological responses. Extending shelf life by delaying the biosynthesis and/or
minimizing the action of the plant hormone ethylene has been an attractive target area of
study for postharvest physiologists. This technique has the potential to reduce damage and
postharvest loss of horticultural products while increasing the shipping range and market
area. This chapter outlines the major advances in our understanding of ethylene perception
in fruits, vegetables, and flowers in the recent past.
6.2 Background on ethylene perception
After ethylene has been synthesized, it is perceived and the signal transduced via a transduction
machinery to trigger specific biological responses. Many key components of the
ethylene signal transduction pathway were identified from a simple genetic screening of the
model plant species Arabidopsis thaliana that made use of ethylene’s effect on dark-grown
seedlings known as the “triple response.” The triple response is characterized by the inhibition
of hypocotyl and root elongation, a thickening of hypocotyl, and an exaggerated apical
hook. (An illustration of the “triple response” using dark-grown melon seedlings is shown
in Fig. 6.1.) Taking advantage of the triple responses, populations of mutagenized Arabidopsis
were screened for seedlings that displayed an altered triple-response phenotype,
and this approach resulted in the identification of several ethylene-insensitive mutants.
These mutants include those that are insensitive to the ethylene receptors etr1 (ethylene
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