Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

204 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
Aromas
Choline released (nmol/mg
protein)
(a)
50.00
45.00
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
D
G1
B
Mitochondrial membrane
Microsomal membrane
A
B
BC
D
D CD
DE
E
G2 W T R
Development stag
Seascape
Choline released (nmol/mg
protein)
50.00
45.00
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
C
A
D
C C C B
C
Mitochondrial membrane
Microsomal membrane
G1 G2 W T R
(b)
Development stag
Fig. 9.6 Stage-specific changes observed in PLD activity of strawberry varieties (Fragaria ananassa Duch. cv.
“Aromas” and “Seascape”). Fruits were collected at various developmental stages for the isolation of mitochondrial
and microsomal membranes, designated as 1—young immature (G1); 2—young expanding (G2); 3—mature
white (W); 4—turning orange stage (T); and 5—firm ripened stage (R). PLD activity was measured by the
release of radiolabeled choline from 16:0/16:0 phosphatidylcholine (L 3 -phosphatidyl (N-methyl- 3 H) choline,
1,2-dipalmitoyl) in a 1-mL reaction mixture. The values are mean ±SE from three separate experiments. The
histograms with different alphabets indicate that the values are significantly different at p ≤ 0.05 (generalized
linear model procedure, SAS programme, SAS Institute Inc.). (Reproduced with permission from Yuan et al.,
2005.)
D
D
micromolar levels of calcium plus PIP 2 at a pH of 4.5–5.5 (Wang, 2000). The physiological
implication of this effect is that PLD action will be stimulated under conditions when membrane
compartmentalization is lost or the cytosol is acidified as happens during ripening
and senescence. In vivo, PLD is compartmentalized in tomato fruit, and can be visualized
by immunochemical localization in the cytosol, plasma membrane, endoplasmic reticulum,
vacuole, and mitochondria (Pinhero et al., 2003). As well, during fruit development there
is increased binding of PLD to the ER and plasma membrane, potentially in response to
increased cytosolic calcium (Pinhero et al., 2003; Yuan et al., 2006a). Thus, under in vivo
conditions, PLD is not exposed to acidic conditions except when it is compartmentalized
in the vacuole or when it is exported into the cell wall compartment (Yuan et al., 2006a).