248 P. BISWAS ET AL.
Harpster 2001). Pectin is the most abundant class of macromolecule
within the cell wall matrix and in the middle lamella between primary
cell walls. During fruit softening, pectin typically undergoes solubiliza-
tion and depolymerization that are thought to contribute to cell wall dis-
sociation through loosening and disintegration (Brummell and Harpster
2001).
Textural changes occurring in chill-injured tomatoes differ from those
of normally ripening fruit specifically by altering pectin dissolution
(Almeida and Huber 2008). A reduction of pectin solubilization and
depolymerization can be attributed to a higher CI incidence in tomato
(Rugkong et al. 2010). However, pectin depolymerization is not a ubiq-
uitous requirement for pectin solubilization (Brummell 2006). Reduc-
tion of pectin solubilization and absence of pectin depolymerization
may contribute to the abnormal texture of chill-injured tomato fruit
(Jackman et al. 1992; Almeida and Huber 2008). Reduced pectin sol-
ubilization and polymerization in chilled fruit have been observed in
peaches (Brummell et al. 2004), nectarines (Dawson et al. 1995), and
plums (Manganaris et al. 2008). In addition, the degree of chilling-
induced reduction of pectin solubilization and polymerization could
differ depending on the extent of chilling damage (Rugkong et al. 2010).
For many years PG, the most abundant pectin-degrading enzyme, was
thought to be the primary enzyme responsible for tomato fruit soften-
ing (Prusky 1996). PG catalyzes the hydrolytic cleavage of galacturonide
linkages (Giovannoni et al. 1989) which causes pectin depolymeriza-
tion and solubilization (Villarreal et al. 2008). However, their role in
cell wall depolymerization and solubilization is a subject of debate
(Brummell and Labavitch 1997; Almeida and Huber 2008). Molecu-
lar studies revealed that with increasing exposure to chilling tem-
peratures, chilled tomatoes showed a higher reduction in transcript
abundance, total activity, and protein accumulation encoding PG than
non-chilled fruit (Rugkong et al. 2010). Reduced PG activity has also
been reported in chilled mango (Kesta et al. 1999) or peach (Brum-
mell et al. 2004). Cruz-Mend ́ıvil et al. (2015), however, indicated that an
upregulation of cell wall degradation genes include PG after cold stor-
age. Research with transgenic plants introduced doubt as to the exact
association between cell wall degradation caused by PG and tomato
fruit softening (Giovannoni et al. 1989). Suppression of PG activity in
transgenic tomatoes resulted in fruit with altered pectin metabolism
but similar softening to controls (Smith et al. 1988). Jackman et al.
(1992) speculated that softening of chilled fruit after transfer to a higher
temperature was induced by non-extractable PG. Almeida and Huber
(2008) suggested that PG was not a major determinant of softening of