Postharvest Factors Affecting Potato Quality and Storability - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 395

the potato tuber is the most studied example of cork formation (Sabba and Lulai, 2002). The
biosynthesis of the linear long-chain compounds forming the aliphatic suberin domain and
cork aromatic components share a common pathway with cutin and lignin to a certain extent
(Boerjan et al., 2003). The aromatic domain is a polyphenolic substance mostly composed
of hydroxycinnamic acid derivatives. This aromatic domain is believed to link the aliphatic
domain to the cell wall (Kolattukudy, 1980). The biosynthetic pathway for hydroxycinnamic
acid was proposed by Cottle and Kolattukudy (1982) and Bernards and Razem (2001). Per-
oxidase activity associated with suberization has been detected in the potato tuber (Bernards
et al., 1999). Identification of metabolic enzymes involved in aliphatic domain biosynthesis
is limited to isolation from potato tuber disks. Lotfy et al. (1994, 1995) hypothesized that fer-
ulate acyltransferase is involved in linking the aromatic monomer ferulate to the aliphatic do-
main. Recently, Soler et al. (2007) used a comprehensive approach to identify genes involved
in suberin biosynthesis by developing microarrays from expressed sequence tags (ESTs)
obtained from the suppression subtractive hybridization method. Out of 236 ESTs analyzed,
135 sequences showed homology to unique genes playing a role in cork biosynthesis.
Using histological methods, Sabba and Lulai (2002) compared the process of maturation
in native periderm and wound periderm. In the case of wound periderm, staining with ruthe-
nium red and hydroxylamine-FeCl 2 revealed that cell walls lack the pectins that allow the
formation of calcium pectate in native periderm to strengthen cell walls. Peroxidase stain-
ing is more prominent in native periderm. Schreiber et al. (2005) compared the efficiency
of wound periderm with native periderm for peridermal transpiration, and concluded that
wound periderm is not as efficient as native periderm and significant water loss can occur
even after wound healing. The qualitative differences in chemical composition between the
two periderms are very minute, but the water loss in native periderm is 5-10 times higher
even after 1 month of suberization.
19.3 Dormancy
Length of dormancy is an economically important trait in potato tubers. Understanding the
dormancy process and the ability to manipulate these processes are important to increase
storability and the availability of potatoes throughout the year. Dormancy is often described
as a resting stage where growth pauses and tubers will not sprout even when placed under
ambient conditions favorable for growth (Burton, 1989). Dormancy is necessary for plant
survival and development. Potatoes remain dormant for a set period of time after harvesting
depending on the cultivar. Potato dormancy starts at tuber initiation because the apical
bud of the stolon remains dormant during tuber development and enlargement (Burton,
1989). Potato tuber meristems are described as endodormant, where growth inhibition is
due to the effect of biochemical factors within the tuber (Hemberg, 1985). Dormancy is
regulated by variety of factors such as genotype, physiological age of the tuber, and plant
hormones. Dormancy-related mechanisms are controlled by four plant hormones (abscisic
acid (ABA), cytokinin, gibberellic acid (GA), and ethylene) along with environmental
factors and photosynthesis (Suttle, 2000).
19.3.1 Status of molecular-level understanding on dormancy
Most of the recent knowledge on hormonal interaction and mechanism during dormancy
comes from the model plant system Arabidopsis . ABA is a dormancy-inducing agent, as