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Fig. 9.3
Fracture face of a fully open carnation flower petal showing cell wall (CW), protoplasmic fracture face
of the plasma membrane (PM), cytoplasm (CY), and vesicles in the cytoplasm (thick arrows). Bar
=
100 nm.
(Reproduced with permission from Paliyath and Thompson, 1990.)
C
2
H
4
Ethylene
receptor
Gene
expression
Ca
H
Phospholipase D
H
Ca
H
Ca
Phospholipid
Phosphatidic acid
Outside
Inside
Autocatalytic
H
Phosphatidate
phosphatase
Ca
Ca
PLD
Increased cytosolic
Ca
2+
, H
+
Diacylglycerols
H
Ca
Ca
2
Outside
Inside
Lipolytic acyl
hydrolase
H
Ca
Ca
H
Calmodulin
Ca
Leakage
H
Ca
PLD
Free fatty acids
Ca
PLD
PLD
Ca
Damage to Ca
2+
-H
+
ATPase
Fatty aldehydes
Gel-phase
formation, reduced
membrane fluidity
Alkanes
Lipoxygenase
Peroxidized fatty
acids
Free radicals
Fig. 9.4
Schematic representation of various reactions involved in membrane deterioration. The autocatalytic
nature of the cycle derives from the accumulation of lipid degradation products in the membrane that causes
progressively increasing membrane destabilization and loss of membrane compartmentalization. Part of this cycle
is also shared with phospholipid biosynthetic pathways.
201
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