A common feature of most biennial vegetables is accumulation of
mainly soluble carbohydrates in the storage organ during the first year.
These carbohydrates are essential as fuel for respiration during winter
dormancy and subsequent regrowth in the second season. Storage of bi-
ennial vegetables at 0–5°C for six months or more should not, due to
the low metabolic activity, result in depletion of soluble carbohydrates
that may promote senescence. After termination of dormancy and ver-
nalization, the apex of cabbage and onions exerts an increasing sink
strength with translocation of carbohydrates from the leaves to the core
leading to senescence of the outer leaves with the senescence signal prob-
ably originating from the apex.
Fruit ripening can be considered as a presenescence phase since the
fruit flesh will ultimately senesce with dispersal of the seeds. Ripening
of fruits shows both similarities and differences compared with vegeta-
tive plant organs. Degradation of chlorophyll with or without synthesis
of carotenoides is a part of the ripening process in some fruits while
other fruits like kiwi and avocado remain green. Accumulation of free
amino acids due to proteolysis, a common feature in leafy vegetables
during senescence, is absent in fruits; instead synthesis of new proteins
prevails. Changes in cell wall structure and composition occur during
senescence of many plant organs but softening similar to that in fruit
tissue is absent in leaves, stems and storage organs.
The physiological basis for fruit storage is closely associated with the
stage of development at harvest and the rate of subsequent ripening and
senescence. The eating quality of most fruit is dependent on proper tim-
ing and balance between the cascade of enzymatic processes each hav-
ing its own temperature dependence. For most fruit the optimum ripening
temperature is between 15 and 25°C independent of ripening behavior
(climacteric-nonclimacteric) or sensitivity to chilling injury. On the other
hand, some fruit store best at a temperature just above zero, some fruits
should not be stored below 5°C, while those suffering from chilling in-
jury have a temperature optimum ranging from 12 to 15°C. Generally,
unripe fruits are more sensitive to chilling temperatures than ripe fruits.
Climacteric fruits are harvested preclimacteric with storage and han-
dling methods aimed at inhibiting or delaying ripening until retailing.
Although the synthesis of ethylene is on a low level in preclimacteric
fruits, ethylene seems to play a crucial role during the onset of ripen-
ing. Too early harvest could result in an inability to ripen properly due
to the absence of activated ethylene receptors (Lelièvre et al., 1997).
Ethylene could also be used to promote fruit ripening (Reid, 1992).
Physiology of Storage 111