全 文 ：广 西 植 物 Guihaia 25(2)：164— 168 2005年 3月
镉诱导萝 卜幼苗活性氧产生、脂质
过氧化和抗氧化酶活性的变化
刘云国，汤春芳，曾光明，徐卫华，李程峰
(湖南大学环境科学Lj工程系，湖南长沙 410082)
摘 要：通过水培试验，研究 Cd 胁迫对萝 卜幼苗活性氧的产生、脂质过氧化和抗氧化酶活性的影响。超氧
阴离子(0_)的产生速率和丙二醛(MDA)的含量与对照相比有不同程度的增加，表明 Cd 胁迫能导致萝 卜
体内的氧化胁迫；超氧化物歧化酶(SOD)的活性，随着 Cde+浓度提高，首先明显上升，然后逐渐下降，甚至低
于对照，叶片过氧化氢酶(CAT)的活性明显增加，根系CAT活性则减少，根系以及较高浓度Cdz 处理后期叶
片谷胱甘肽还原酶(GR)的活性均显著增加。推测：胁迫初期可能主要由 SOD和CAT发挥抗氧化作用；后期
由于抗坏血酸 谷胱甘肽(AsA—GsH)循环途径的激活，以及还原型谷胱甘肽(GSH)和植物络合素(Phytoch—
elatins，PCs)的合成，可能在清除活性氧或者直接鏊合Cd2+中起作用。
关键词：镉；氧化损伤；抗氧化酶；水培；萝 h
中图分类号：Q945 文献标识码：A 文章编号：l000—3l42(2005)02—0l64—05
Jr’1 1 ● ● 1 1 ● 1 ● · ‘
acIm iUm —lncIucecI SUDeroxide an1on ~eneration，
一● ● 1 ‘ 1 ·‘ 1 _ n ·· ‘ 1 · llplcIDeroxidation and chan~es 0tantioxidant
enzyme activities in radish seedlings
LIU Yun—guo，TANG Chun—fang，ZENG Guang—ming，
XU Wei-hua．LI Cheng—feng
(Department of Environmental Science and Engineering，Hunan University，Changsha 4 1 0082．China)
Abstract：While seedlings of radish raised in increasing contents of Cd!+ in hydroponic system，increment in
ratio of superoxide dismutase(SOD)／catalase(CAT)and levels of superoxide anion(OT)and lipid peroxides
were observed；125／~mol,／L Cd treatment resulted in a gradual elevation in SOD activity；while at Cde level
of 250 and 500／xmol／L，SOD activity considerably increased at first，then declined to even lower than that of
the contro1．CAT activity showed enhancement in leaves whereas decrease in roots．Cd2叶。induced an obvious
elevation in GR activity in both roots and leaves．A marked elevation in GR activity suggests that ascorbate—
glutathione(As人一GsH)cycle may be activated to scavenge AOS and the synthesis of reduced glutathione
(GSH)may be stimulated for subsequent synthesis of ph ytochel atins(PCs)to chelate Cd2+ directly．
Key words： cadmium ；oxidative stress；antioxidant enzymes；hydroponic CHIture；radish
Even under natural conditions of growth and
development，plants face constant risk from active
oxygen species(AOS)，including 07，hydrogen per—
oxide(H2 02)，hydroxyl radical(。OH )inevitably
generated via number of metabolic pathways．AOS
play important roles in plant’S defence system a—
gainst pathogens，mark certain developmental sta—
ges such as lignification and other cross—linking
收稿 日期：2004—02一l 2 修订 日期：2004—05一l8
基金项目：国家 863高技术资助项目(NO 2001AA6 14020)
作者简介：刘云国(1 955一)，男．湖南常德市人，教授．博士生导师，长期从事环境科学研究。E—mail：liuyunguo@hnu．cn
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2期 刘云国等；镉诱导萝 f、幼苗活性氧产生、脂质过氧化和抗氧化酶活性的变化 165
processes in the cell wall and act as intermediate
signaling molecules to regulate the expression of
genes，while excess AOS can damage membrane
lipids，proteins，pigments and nucleic acids，resul—
ting in dramatic reduction of productivity，finally
the death of plants(Hegedfls et a1．，2001)．To avoid
oxidative damage，pl ants have evolved various protec—
tive mechanisms，one of which is the enzymatic antioxi—
dant system operating with the simultaneous and se—
quential action of number of enzymes such as SOD，
CAT，peroxidases(POD)and GR．
Heavy metals can ca use molecular oxidative dam—
age to plants either directly or indirectly through the
formation of AOS(Gallego et“Z．，1996；Cho et aZ．，
2000；Malecka el a1．，2OO1；Shah et a1．，2001)．
Understanding the biochemical detoxification
strategies that plants adopt against oxidative stress
is a key to manipulate heavy metal tolerance in
plants．Cadmium(Cd )is phytotoxic strongly and
can cause growth inhibition and even plant death．
Some studies related t o change of antioxidant enzyme
activities and AOS level under Cd stress have been
carried out(Yan et a1．，1997；Luo et a1．，i998；Wang et
a1．，2002；Ren et“Z．，2002；Xu et“Z．，2001)，however，
there are few researches analyzing entirely the change
of AOS。MDA content and activities of antioxidant en—
zyme in roots and leaves of plants．
Radish is a heavy metal tolerant plant． The
aim of this study was to investigate the responses
of OT-generation，lipid peroxidation and SOD，CAT，
GR activities to Cd。 treatment in radish seedlings and
afford general referenced evidence for phyto-remedia—
tion of soll contaminated by heavy meta1．
1 Materials and Methods
1．1 Plant culture and treatment conditions
Seeds of three radish(Raphanus sativus L．)
varieties were surface sterilized with 3．5 NaC1O
for 20 min and rinsed thoroughly with distilled wa—
ter，after 3 d germination on moistened filter paper
in dark at 25℃ with humidity of 70 ～ 80 ，the
seeds were transferred to a greenhouse maintained
at 26℃／20℃ day／night with 70％～80 humidi—
ty and a 16 h photoperiod at 300 gmolm。 s。 in an a—
erated hydroponic system in pot s containing 1． I
Hoagland nut rient solution replaced twice a week．
A small experiment on each variety was con—
ducted with ten—daY old plants in nutrient so1ution
containing 250 gmol／L Cd” for 2 d．Based on the
growth of these varieties．“No13 Jinhan brand”was
selected as materia1．After growing in the nutrient so—
lution for 20 d。plants were subjected to 0，125，250，
500 utool／L Cd。 treatment，which were 1abled as
Cd0，Cdl，Cd2，Cd3 treatment respectively．Roots and
1eaves from each treatment were collected at 0，12，36，
60。96 h and stored at一40℃ for further analysis．
Experiments were performed in triplicate and
the results are the means± S．D(standard devia—
tion)． The analysis of significant difference be—
tween contrO1 and each treatment were performed
using SPSS statistical software．P≥0．05，P<0．05
and P< 0．0 1 indicates respectively that difference
is not significant，significant and quite significant．
1．2 Enzyme extraction and assays
The following steps were carried out at 4℃ ．
The root or 1eaf tissue(3：1 buffer vo1ume：fresh
weight)was homogenized in a pestle and morlar
with 100 mmol／L，pH7．5 potassium phosphate
buffer containing 1 mmol／L Na2一EDTA，3 mmol／L
DI dithiothreitol，5 (W／V)insoluble polyvinylpyr—
ro—lidone． The homogenate was filtered through
muslin cloth and centrifuged at 10 000× g for 30
min and the supernatant was kept in separate aliquots
at一40℃ ，prior to CAT，SOD and GR analysis．
Content of o was determined as described by
Wang(1990)；SOD activity were estimated accor-ding
to Cho et a1．(2000)；CAT and GR activities were as—
sayed as described by Vitoria et a1．(200 1)；Ⅳ[[)A con—
tent was assayed according to Gallego et a1．(1996)．
2 Results and discussion
2．1 Efect of cadmium on rate of 07generation
Study has demonstrated that Cd can lead to
an elevation in O generation(Shah et“ ．，200i)．
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l66 广 西 植 物 25卷
The change of rate of OTproduction is presented in
Fig．1．07 generating rate elevated with the incre
ment of Cd抖 content especially in roots，with the
increase in time of Cd。+ treatment it increased at
first，then declined，at 1ast elevated again．the maxi—
mum was 1．77，2．14 times higher in leaf at 36 h
whereas 2．30，2．65 times higher in root at 12 h Cd2
treatment respectively than that of contro1．Statistica1
analyses indicated that the diferences of 07 level in
both leaves and roots were not significant，significant
and quite significant respectively under Cdl，Cd2 and
Cd3 treatment compared to C：dO treatment．
1 8O0
1 5 00
1 2 0O
900
600
300
1 800
t 5 00
1 2 OO
9OO
6OO
3OO
O 1 2 3 6 6O 96
O 1 2 36 60 96
时间 Ti me (t／h)
Fig．1 Effect of Cd + stress on generation
rate of O of radish seedlings
2．2 Effect of cadmium on S0D activity
As it is shown in Fig．2，Cdl treatment resul—
ted in a gradual ele＼’ation in SOD activity；while un—
der Cd2．Cd3 treatment SOD activity considerably
increased at first。then declined to even 1ower than
that of controls．The differences of SOD activity
between Cdl，Cd2，Cd3 and CdO treatment did not
reach significant levels．Compared to 0 h Cd2 treat—
ment，the differences were quite significant at 36 h in
1eaves and 12 h Cd2 treatment in roots，while at 36，60
h Cd抖 treatment．it was only significant．
2．3 Effect of cadmium on GR activity
GR can be activated relatively more in roots
●
than in 1eaves。f Cd。 treated pea plant s(Dixit f
d Z．，200 1)．Fig．3 indicates that a significantly in—
crease in GR activitY was recorded in roots and on一
1 2OO
1 OOO
8OO
6OO
400
2OO
l 2OO
1 OOO
8OO
6OO
400
2OO
—
Lea f ⋯ ⋯
! 一
O 1 2 3 6 60 9 6
时间 Ti me (t／h)
Fig．2 Effect of Cd stress on SOD
acti x，ity of radish seedlings
ly under higher Cd level treatment could an obvi—
OUS elevation in C-R activity be detected in leaves．
1．1l，2．1l，2．89 times increase in roots whereas
0．50，1．67，2．0 times increase in 1eaves in GR activ—
ity was noted after 96 h Cdl，Cd2，Cd3 treatment．Cd3
treatment leaded to a quite significant difference in GR
activity in both roots and 1eaves，while Cd2 treatment
caused a significant difference only in roots．Compared
to 0 h Cd treatment．only after 96 h Cd stress had
a significant difference in roots GR activity．
40
32
24
1 6
8
O
40
32
24
1 6
8
O
．
Le。f
— — —●． cd2 —— c d ‘ 1r～ u 7 — u
。
、
E二
。 一
t ——1
o t K O
／
／．
．
’
l 一
O 1 2 3 6
时间 T i me
60 9 6
(t／h)
Fig．3 Effect of Cd2 stress on GR
activity of radish seedlings
2．4 Effect of cadmium on CAT activity
CAT，located in peroxisomes，mitochondriaI
and cytosol，can scavenge H2 O2 withour co—sub一
一； ∞、j— =三 u 00∞
一 二^j lI亡、．0z一0_』】 一 L_0 二0，)．～0
一； LJ—E、一。uJI1一 一>一一。 0
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2期 刘云国等 ：镉诱导萝 卜幼苗活性氧产生、脂质过氧化和抗氧化酶活性的变化 167
strates(Hegedos et a1．，2001)．The change of CAT
activity is showen in Fig．4．W ith increase in time
of Cd stress．an apparent increase followed by a
light decrease was reported in CAT activity in leav—
es；whereas a concomitant decrease in roots CAT
activitY was observed． Compared to Cd0 treat—
ment，Cd2，Cd3 treatment leaded to a significant
difference of CAT activity in leaves，whereas a sig—
nificant and quite significant difference respectively
in roots．Compared to 0 time of CdH treatment．
the difference which was not significant in roots
reached quite significant levels at 36 h and was sig—
nificant at other time of Cd treatment in leaves
．
45O
3 6O
2 7O
1 8O
9O
O
450
3 6O
2 7O
1 8O
90
O
O 1 2 3 6
时间 Tlme
60 9 6
( ／h)
Fig．4 Effect of Cd2 stress on CAT
activity of radish seedlings
2．5 Effect of cadmium on lipid peroxidation
Though antioxidant system can protect far—
thest plant against oxidative damage，the protection
capacitY is limited． Under serious stress condi—
tion，‘0H can be formed through 07-reaction with
H2 02 and lead to lipid peroxidation
． Enhanced lipid
peroxidations have been reported under heavy meta1s
stress(Cho et“ ．，2000；Shah et“ ． ，200l；Luo tⅡ ．，
1998；Chaoui et a1．，l997)．The level of lipid peroxides
was measured in terms of MDA content(Fig．5)
． With
increase in Cd stress level and time，a gradual in—
crease in MDA level was observed
．
Compared to Cd0
treatment，only under Cd3 stress could a significant
difference of MDA level be seen
． The difference
reached significant and quite significant levels respec-
tively at 36 h and 60，96 h Cd。 treatment
；
l上
2 2O
1 8O
{40
1 OO
6O
2 2O
1 8O
1 40
1 OO
6O
O 1 2 3 6 60 9 6
时间 Time (t／h)
Fig．5 Effect of Cde stress on MDA
level of radish seedlings
3 Discussion
Though oj is rapidly dismutated either non—
enzymically or via SOD to H2 O2 and the half life
time is less than a second，increase in OT-generation
under pathogen attack，salinity and signification is
also observed and it is associated with either acti
vation of NAD(P)H oxidase or apoplastic peroxi—
dase(Shah et“ ．，2001)
． Cd is not a redox meta1
like Cu and Fe，and therefore cannot catalvse Fen—
ton type reactions yielding AOS． Up to now，the
reason of AOS generation under Cd?’st ress is not
consistent．First，Cd can produce disturbances in
the electron transport rates of photosystem I and
1I，leading to the production of AOS(Hegedas t
“ ．，2001；Sandalio et“ ．，2001)；secondly，Cd。 is
known to t rigger the oxidation of NADPH causing
07 generation(Aravind et a1．，2003)；thirdly，Cd。+
can disturb the function of antioxidant svstem re
suiting in Oj and H 2O2 accumulation(Luo．1998：
Schhtzend0bel et“ ．，2002)which is impossible in
our study because SOD activity increases rapidly
with the increase in O~generation．The generation
of O is probably due to the oxidation of NADPH
which needs further confirmations
．
SOD is located in various cell compartments
oE5 ∞_4u00 <口
一≥_] c—E、一oEj— 一>一 。 J_<。
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168 广 西 植 物 2 卷
and catalvze dismutation of O or HO2 to H 2 O2
and O2．Under natural physiological conditions，an
inc．rease in OTlevel can induce an elevation in SOD
activity，however，the physichemical properties of
SOD can be changed by H 2O2 and oH ，such as
lOSS of Cu and Zn of Cu，Zn—SoD，and the inhibition
in SoD activity increases with the increase in H2 O2
level(Aravind et a1．．2003；Fang et a1．，2002)．The
increase in SOD activity in response to early Cd。
stress is possibly attributed to the de—novo synthe—_
sis of the enzymic protein(Shah et“Z．．2001)be—
sides the direct induction of 07．However，long
term higher level of OTcould increase H 2 O2 content
and cause a marked decline in SOD activity，sugges—
ting SOD has a limited function in scavenging O7．
Similar result has been obtained in tobacco leaves
under Cd。 stress(Yan et a Z．，1997)．
Fhe increase in leaf CAT activity similar to
the report by Vit0ria et a1．(2001)is probably due
to Cd 。induced an increase in H 2 O2 content in per—
oxisomes(Romero et a Z．，1999)．Contrary to leaf
CAT．CAT activity lii roots declined which may be
explained as following：CAT enzyme is sensitive to
07and can be inactivated by its increasing levels
(Aravind et aZ．，2003)；A decrease in the protein con—
tent led to a decline in activity of CAr(Shah et a1．，
2001；Sandalio et a1．，2001)；POD are widely accepted
as“stress enzymes”，APX can also eliminate H2 Oz and
has higher affinity with H2 O2 than CAr．A marked
increase in GR activity will activate AsA—GsH cycle in
roots．suggesting that an increase in APX activity is
more probable in roots under Cd” treatment．
In a variety of organisms．ectopic over expres—
sion of SOD can cause an excess of the SOD activi
ty relative to the H2 O2 quenching activity，under
this conditions，the activity of SOD may not be e—
nough to scavenge al O7，but may be sufficient to
generate more H 2 O2 than in control，highly reactive
‘()H would then be formed by the reaction of the
remaining OT with H2 O2．Increase in the ratio of
SoD to CAT and POD activity．rather than individ—
ual changes in the activity of each enzyme，would
1cad to oxidative stress(Shan et a Z．，2001)．Table
1 shows that the ratios of SOD／CAT in roots and
in most of the cases in leaves increased with in—
creasing Cd toxicity，whereas the increase in GR
activity may cause increase in POD activity thus
the ratio of SOD／POD possibly did not show a def—
inite change． Our results show that Cd can in
duce oxidative stress through elevating the ratio of
SOD／CAT in radish plants．
GR．a crucial enzyme in AsA—GsH cycle．reduces
oxidized glutathione(GSSG)to GSH and plays an es—
sential role in the protection of chloroplast against oxi—
dative damage by maintaining a high ratio of GSH／
GSSG(Pastori et a1．，1 992)．Cd。 can inactivate GR
via directly or indirectly induced AOS generation
(Schntzend【】bel ￡“Z．，2002)，and can also elevate GR
activity due to the denovo synthesis of enzyme protein
(Vit6ria et a Z．，2001；Dixit et a Z．，2001)．GSH can
be used to form PCs in higher plants．Ascorbate
peioxidase(APX)increases following exposure to
Cd (Heged~s et a1．，2001；Dixit et a1．，2001)．
Taking into consideration data above．the increase
in GR act ivity would suggest AsA—GsH cycle may
be activated to scavenge AOS and the synthesis of
GSH may be stimulated for subsequent synthesis
of PCs to chelate Cd directly．
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