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Legume Genomics and Genetics 2012, Vol.3, No.2, 8
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Figure 3 Effects of three plant extracts on CAT activity in soybean
Note: The same as figure 1
caused strong damage to soybean seedling and
dodder, while the
Melia azedarach
bark extract at high
concentration only did great harm to dodder but safe
for soybean, which suggested
Eucalyptus
extract
could not be used for the prevention and treatment of
dodder in soybean fields, whereas the
Melia
bark
extract would be expected to develop a biological
pharmaceutical for the control of dodder in soybean fields.
Plants can produce a certain amount of reactive
oxygen free radicals in normal environment or in
adversity. In normal physiological condition, production
and scavenging of active oxygen in plants is in a state
of dynamic equilibrium. CAT, SOD, POD and other
enzymes coordinate with each other to keep the
reactive oxygen free radicals in the plants at a low
level, so the plant cells are preserved from harm; in
contrast, the metabolic balance of production and
scavenging of active oxygen was damaged under
stress conditions, that is, excessive accumulation of
reactive oxygen leads to the plant cell membrane lipid
peroxidation, which resulted into the destruction of
cell membrane structure and function; demonstrating
the injury symptoms (Hernandez et al., 2003; Apel
and Hirt, 2004). It was indicated that activity changes
of these three enzymes in plants could be used to
evaluate the extent of plant hurt, which provided a
theoretical basis for the selection of the secure extract
for the host soybean.
This study demonstrated the extracts of
Eucalyptus
robusta
leaves and
Melia azedarach
bark had different
effects on the protective enzyme system of the host
soybean leaves. Although both treatment groups
caused the obvious elevation of SOD activity,
producing more poisonous H
2
O
2
, they had obviously
different effects on POD and CAT, which were
eliminating H
2
O
2
. When the soybean was dealt with
the extract of
Eucalyptus robusta
leaves, activity of
POD went up obviously, while the CAT activity
merely was a little higher compared to the control
group; when the soybean was dealt with the extract of
Melia azedarach
bark, activity of CAT went up
obviously, while the POD activity was no significantly
affected. Taking the extent of hurt into consideration,
we can draw the conclusion that the degradation of
poisonous H
2
O
2
in soybean leaves is mainly coupled
with CAT, then POD, namely, SOD activity obvious
elevation produced much poisonous H
2
O
2
; whereas,
the enzyme activity of CAT, carried on eliminating
H
2
O
2
, was
relatively weak, caused H
2
O
2
accumulation
in vivo,
which was the physiological mechnism of
emerging obvious injury symptoms in host soybean.
On
Jerusalem artichoke
, Huang et al (2011) found that
the activity of POD and SOD was obviously higher
than that of CAT, therefore they concluded that the
superoxide anions in
Jerusalem artichoke
leaves is
mainly degraded by SOD-POD, then SOD-CAT.
Similar to the above-mentioned study, in this study,
we found that the effect of SOD-CAT in degradation
of superoxide anions in soybean leaves is apparently
superior to SOD-POD. After the treatment by the
extracts of
Eucalyptus robusta
leaves, low activity of
CAT in soybean seedling leaves can't effectively
eliminate the poisonous H
2
O
2
, developing obvious
injury symptoms; on the contrary, after treated by the
extracts of
Melia azedarach
bark, higher activity of
CAT in soybean seedling leaves can effectively
degrade the poisonous H
2
O
2
, developing no significant
injury symptoms.
In this study, it was concluded that the ethanol extract
of
Melia azedarach
bark can inhibit the growth and
development of the dodder but secure to the host
soybean; hoeever, what substance on earth that inhibit
the growth and development of dodder still remains
unknown. In order to investigate the substance that
significantly inhibit the growth and development of
dodder, further research is needed on isolation and