Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

Chapter 10
Phospholipase D Inhibition Technology
for Enhancing Shelf Life and Quality
Gopinadhan Paliyath and Jayasankar Subramanian
10.1 Introduction
The role of plasma membrane in the preservation of cell structure and integrity was discussed
in the previous chapter. Phospholipase D (PLD) is the key enzyme which initiates a series
of catabolic cascades that lead to the eventual deterioration of the membrane. The deterioration
of the membrane is a part of the development of the organoleptic quality of the fruits
during ripening. However, uncontrolled progression of lipid degradation can reduce the life
of fruits, vegetables, and flowers. Previous technologies for the preservation of horticultural
produce quality were based on the regulation of ethylene biosynthesis (e.g., Retain, Valent
Biosciences, a trade name for the ethylene biosynthesis inhibitor aminoethoxyvinylglycine)
or its action (e.g., 1-MCP, AgroFresh Inc.). Inhibition of cell wall degradation using calcium
chloride was another approach that increased the firmness in fruits such as apple. Biotechnological
approaches for the inhibition of ethylene biosynthesis using antisense ACC synthase
have been found to be an effective approach to enhance fruit firmness in apple fruits
(Cornell University College of Agriculture and Life Sciences, 2002; http://www.nysaes.
cornell.edu).
The process of membrane deterioration during senescence has been well documented
(McKersie et al., 1978; Paliyath and Droillard, 1992). The preservation of membrane integrity
is critical to the maintenance of membrane compartmentalization. As well, membranes
are the sites for several key enzymes including ion transporters such as the proton
and calcium ATPases. The organization of microtubules and the synthesis of cell wall components
are closely associated with the plasma membrane. However, technologies for the
preservation of membrane structure and thereby extending the shelf life of fruits, vegetables,
and flowers have become a reality only recently.
10.2 Phospholipase D and membrane deterioration
Phospholipase D is the key enzyme involved in the initiation of membrane deterioration. In
response to hormones and external stimuli, phospholipase D is believed to become bound to
the membrane initiating a cascade of catabolic reactions leading to the generation of several
neutral lipids, the accumulation of which results in the destabilization of the membrane
(Paliyath and Droillard, 1992). In general, enzymes such as phosphatidate phosphatise,
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