Agriculture Reference
In-Depth Information
(a)
2 ATP 2 ADP
Glucose
2 PGA
2 (1,3-Diphospho-
glycerate)
2 ADP
2 NAD 2NADH
2
2 Ethanol
2 ATP
3
2 PEP
2 Acetaldehyde
2 ADP
1
2 ATP
2 Pyruvate
2 Lactate
2
2 CO
2
Krebs cycle
(b)
Isocitrate
Pyruvate
NAD
NAD
NADH
2
CO
2
Citrate
a
-Ketoglutarate
NAD, ADP
NADH
2
CO
2
Acetyl-CoA
NADH
2
, ATP
CO
2
Succinate
FP
Oxaloacetate
FPH
2
Fumarate
NADH
2
NAD
Malate
(c)
ADP ATP
ADP ATP
ADP ATP
O
2
NADH
2
cyta
3
cytb
cyta
FP
cytc
e
e
e
e
e
OH
−
Figure 6.1
Pathways involved in glucose oxidation by plant cells: (a) glycolysis,
(b) Krebs cycle, (c) mitochondrial cytochrome chain. Under anoxic conditions, Reactions
1, 2 and 3 of glycolysis are catalysed by lactate dehydrogenase, pyruvate decarboxylase
and alcohol dehydrogenase, respectively. ATP and ADP, adenosine tri- and diphosphate;
NAD and NADH
2
, oxidized and reduced forms of nicotinamide adenine dinucleotide;
PGA, phosphoglyceraldehyde; PEP, phosphoenolpyruvate; Acetyl-CoA, acetyl coenzyme
A; FP, flavoprotein; cyt, cytochrome;
ε
, electron. (Modified from Fitter and Hay, 2002).
Reprinted with permission from Elsevier
and the Krebs cycle is suppressed. This leads to an accumulation of acetalde-
hyde—the first end-product of fermentation (Figure 6.1a); synthesis of alcohol
dehydrogenase catalysing the conversion of acetaldehyde to ethanol; and con-
sumption of NADH
2
as acetaldehyde is reduced to ethanol and hence continuing
production of ATP and pyruvate. So fermentation can continue to generate ATP
