264 P. BISWAS ET AL.
IV. Concluding Remarks
Chilling injury in tomato fruit is a physiological disorder with the onset
and severity determined by a combination of storage temperature and
duration of exposure. Failure to ripen properly, uneven blotchy red col-
oration, increased susceptibility to decay and altered aroma profile are
reported to be the main CI symptoms. An increased rate of solute leak-
age in tissues is often correlated with the appearance of CI symptoms
and measurement of CI severity in tomato fruit.
Mechanisms of many chilling-induced physiological alterations can
be confounded with normal ripening-associated changes since some
of the processes occurring during development of CI are similar to
those which occur during ripening and senescence. For example, dur-
ing ripening, fruit soften and show increased disease susceptibility,
increased ion leakage, and increased ethylene production. Most of
these, if not all, physiological and cellular changes may occur after
chilling-induced damage. It is important to differentiate the physiologi-
cal or cellular alterations accompanying ripening from the changes that
reflect chilling damage.
There is a “threshold temperature” for storing mature-green tomato
fruit. Below this threshold temperature, time and temperature together
set the thresholds for onset of damage and different symptoms have
a different time and temperature threshold. There is a temperature
sequence where some symptoms (flavor loss, blotchy red coloration)
are triggered at higher temperature than others (complete inhibition of
red coloration, pitting, or decay). Importantly, if this time–temperature
threshold model for each symptom is valid, it is possible that each
symptom may have an independent response to postharvest treatments
that are employed to alleviate CI.
While CI has been recognized, described, and studied for over
100 years and significant advancement in general understanding of
plant responses to chilling stress have been made, fundamental stud-
ies involving molecular mechanisms of chilling damage, especially at
the proteomic level, are limited. Omics-based approaches have allowed
the complex global biological systems involving various plant func-
tions and responses to be addressed. In this sense, proteomics is a key
tool for identifying functional proteins responsive to low temperature
stress, proteins that act to maintain cellular homeostasis under cold-
stress, and proteins more highly expressed in CI-resistant cultivars.
Since susceptibility to CI varies between cultivars, proteins correlating
with improved CI resistance would be important targets for breeding
programs.