Agriculture Reference
In-Depth Information
eating quality and senescence through its influence on basic structural features
and physiological mechanisms.
Calcium and cell wall and
membrane characteristics
Calcium ions have been shown to bind pectin molecules and Knee and Bartley
(
) suggested that these ions form bridges between pectin molecules in the
middle lamella and are responsible for cell cohesion.
Vacuum infiltration of 'Golden Delicious' apples with calcium chloride,
either soon after harvest or after
months' cold storage, greatly reduces
subsequent fruit softening. Electron micrographs of treated fruits show well-
structured, darkly staining middle lamellae indicative of tightly packed
polyuronides even after prolonged storage, whereas the corresponding un-
treated controls show the middle lamella to have degraded to the point of cell
wall separation (Poovaiah
et al.
,
).
Calciumacetateinfiltrationafteraperiodofeithercoldstorageorcontrolled
atmosphere storage can even largely reverse softening (Table
; Siddiqui and Bangerth,
).
Although net degradation of cell walls takes place during ripening, incor-
poration of labelled methionine and inositol in apple cell wall polysaccha-
rides indicates the synthesis of cell wall polymers during ripening (Knee,
.
;
Poovaiah
et al.
,
).
Calcium also has pronounced effects on cell membranes and retards their
breakdown during storage. Fuller (
) studied membrane changes in 'Cox'
Effect of infiltration at harvest or after cold storage with
glycerol/Tris buffer with and without calcium acetate on the firmness of
fruit tissue from two apple cultivars
Table
.
Infiltration
Firmness (N)
Firmness after
Cultivar
medium
at harvest
weeks at
◦
C
'Cox'
None
.
.
Glycerol
.
.
Glycerol
+
Ca
.
.
'Gloster
'
None
.
.
Glycerol
.
.
Glycerol
+
Ca
.
.
Glycerol
=
mol m
−
glycerol in mol m
−
Tris buffer, pH ..
Glycerol
+
Ca
=
mol m
−
glycerol
+
mol m
−
Ca acetate
in the same buffer.
From Stow (
). Reproduced with permission.
