Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

Chapter 9
Structural Deterioration in Produce:
Phospholipase D, Membrane
Deterioration, and Senescence
Gopinadhan Paliyath, Krishnaraj Tiwari, Haiying Yuan, and Bruce D. Whitaker
9.1 Introduction
Ripening and senescence are the ultimate phases in the developmental events of fruits that
result in the expression of the quality characteristics inherent to the fruit. Although it is
difficult to demarcate a dividing point between ripening and senescence, the former can
be designated as the quality-developing phase, whereas the latter predominantly involves
the loss of quality. Degradation of structural elements such as the cell wall and the plasma
membrane is an inherent feature of ripening and senescence. Wilting of flowers also involves
similar deteriorative changes. Harvested vegetables, when exposed to abiotic stresses such
as heat, cold, and water deficit, undergo deteriorative changes in the cell membrane that
result in the loss of quality. Seasonal changes that result in a decrease in light duration and
intensity, temperature, etc., are natural cues for the initiation of ripening in fruits. Often
such changes are associated with the biosynthesis of ethylene, which is also an initiator of
ripening in many fruits and senescence in leaves. At the ultrastructural level, the events that
occur during ripening and senescence reflect the deterioration of cellular structures, and in
particular the cell membrane, which results in a loss of compartmentalization of ions and
metabolites, leading to the loss of tissue structure and ultimately homeostasis.
The importance of regulating the deteriorative events that occur during ripening and
senescence has been well recognized. Consequently, several scientific approaches and technologies
have been developed with the objective of enhancing the shelf life and quality of harvested
fruits, vegetables, and flowers. Some of these include attempts to stabilize the cell wall
by the application of calcium, biotechnological approaches to inhibit cell wall–degrading
enzymes, and modification of the ethylene biosynthetic pathway through inhibition of key
enzymes (e.g., inhibition of ACC synthase by the application of aminoethoxyvinylglycine
(AVG), commercially available as “ReTain” (Valent Biosciences)), and biotechnological
approaches (e.g., antisense transformation of apple, tomato, and melon for ACC synthase
or ACC oxidase). Inhibiting ethylene action through the application of the ethylene antagonist
1-methylcyclopropene (SmartFresh, AgroFresh, Inc.) has become a practice of both
basic biological and practical interest. Application of 1-MCP has been successfully used to
extend the shelf life of fruits (e.g., apples and pears) and flowers. The cell membrane is a
key site where senescence-dependent changes are observed to occur earlier than most other
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