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Effect of Rare Earths on Plants under Supplementary Ultraviolet-B Radiation: II. Effect of Cerium on Antioxidant Defense System in Rape Seedlings under Supplementary Ultraviolet-B Radiation
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JOURNAL OF RAKE EAKTHS 24 (2006) 364 - 368
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Effect of Rare Earths on Plants under Supplementary Ultraviolet-B Radiation: 1 Effect of Cerium on Antioxidant Defense System in Rape
.
Seedlings under Supplementary Ultraviolet-B Radiation Liang Chanjuan (LWB)',Huang Xiaohua (*&+)', Tao Wenyi (psISt#)', Zhou Qing (PI * ) I * ( 1 . The Key Laboratory of Industrial Biotechnology , Ministry of Education, Wuxi 214036, China ; 2 . College of Chemistry & Environmental Science , Nanjing Normal University , Nanjing 210097, China ) Received 10 June 2005; revised 26 August 2005
Abstract: Effects of cerium ( Ce3 ) on membranous protective enzymes in rape seedlings exposed to two levels of enhanced ultraviolet-B radiation (UV-B , 280 320 nm) were studied by hydroponics in the laboratory. The results show that the chlorophyll content decreases and membrane permeability increases in the leaves under UV-B irradiation with an intensity of 0.15 and 0.35 W.m-2. The activities of SOD, CAT and POD are first increased and then decreased in leaves exposed to a low level of UV-B radiation. POD activity in leaves exposed to a high level of UV-B radiation is enhanced constantly. The sensitivities of these enzymes to UV-B radiation are SOD > CAT > POD. The injury by UV-B radiation on the functions of protective enzymes is lightened, their ability to scavenge radicals is improved, and the membrane permeability is maintained by Ce . Furthermore, the protective effect of cerium is more obvious in plants exposed to low levels of UV-B radiation than to high levels of it. Accordingly, all results prove that the protective effect of Ce on plants under UV-B radiation is realized through the protective system of plants. +
-
Key words : cerium ; elevated UV-B radiation ; rape seedlings ; protective enzymes ; membrane permeability ; rare earths Document code: A CLC number: 0614.3 Article ID: 1002 - 0721(2006)03 - 0364 - 05
The increase in ground level ultraviolet-B radiation (UV-B, 280 320 nm) as a result of stratospheric ozone depletion may have major deleterious effects on crop photosynthesis and production. As one major environmental problem, it has attracted more and more attention of researchers, and therefore there have been substantive and timely reports, providing abundant information about the damage of UV-B radiation on crops. However, the studies about the ecological protection of plants against damage of UV-B radiation are comparatively few. We have previously reported that Ce can alleviate the suppressive effect of
-
supplementary UV-B radiation on growth and photosynthesis in rape seedlings"]. In addition, it is clear to us that the improvement of photosynthetic function in leaves with Ce treatment is one of the direct causes preventing rape seedlings worsening under UV-B radiation. The supplementary UV-B radiation induces overproduction of free radicals and results in oxidation of lipids in plant tissues as reported by Hernan"]. Furthermore, the decrease in biomass is closely related to the breakage of the cell membrane in plant tissues, because of the damage of UV-B radiationL3'. Consequently, it is necessary to assess the effect of Ce on
* Corresponding author (E-mail : zhouqeco@yahoo. com .cn ) Foundation item: Project supported by the National Natural Science Foundation of China (30570323. 20471030) and the Foundation of State Planning Committee (IFZ20051210)
Biography: Gang Chanjuan (1978 - 1, Female, Doctor candidate Copyright 0 2 0 0 6 , by Editorial Committee of Journal of the Chinese Rare Earths Society. Published by Elsevier B .V . All rights reserved
Liang C J et a1 . Effect of Cerium on Antioxidant Defense System in Rape Seedlings
the antioxidant enzyme system in plants under supplementary UV-B radiation. On the basis of earlier investigations, considering the antioxidant enzymes scavenging free radical as the research objects, we investigated the irritability response of these enzymes, including Superoxide dismutase ( SOD ), catalase (CAT), and peroxidase (POD) to UV-B radiation, as well as the regulation of Ce on them under such adverse stress.
1 Materials and Methods 1.1 Plant culture The rape ( Brmsica juncea L . ) seeds of “Shilifeng ” were sterilized and cultured according to Ref. [ 11.
1.2 Treatments The optimum concentration of the CeC13 solution was 12 mg.L-l, which was determined in the pre-experiments. The CeC13 solution was sprayed evenly on the leaves until drops began to fall. The same amount of distilled water was applied for CK . After 48 h , half of the seedlings pretreated with Ce were placed under ultraviolet lamps. Enhanced UV-B radiation was performed with 40 W UV-B lamps, produced by Nanjing Lamp Factory, hanged perpendicularly over the plants. The levels of UV-B radiation were 0.15 and 0.35 W m2, which were measured with an ultraviolet radiometer, made by photo-electricity instrument factory of the Beijing Normal University. Seedlings were irradiated for 5 h from 1O:OO to 15:00, for a total of 6 d . The height of the lamps over the plants was adjusted to maintain consistent radiation intensity. There were 6 sample sets in the present experiment: controls (sprayed with deionized water), Ce (sprayed with CeC13 solution ) , TI ( irradiated with 0.15 W*rn-’ UV-B), T2(Irradiated with 0.35 UV-B) , Ce + TI(sprayed with CeC13 solution and then exposed to 0.15 UV-B radiation), and Ce + T2( sprayed with CeC13 solution and then exposed to 0.35 W m-’ UV-B radiation). There were 3 replicates for each set and 3 pots per treatment.
1.3 Determination The physiological indices were measured at 1O:OO every day for a total of 5 d after the treatments with Ce and UV-B radiation were finished. Total chlorophyll content (Chl content) , Cell membrane permeability ( E % ) , and POD activity were determined according to Ref. [ 41 . CAT activity was measured with
365
the method described in Ref. [ 5 1 . SOD activity was measured with the reagent box produced by Nanjing Jiancheng Bioengineering Institute.
2 Results and Discussion 2.1
Effect of Ce on chlorophyll content and membrane permeability in rape seedlings under W - B radiation
2.1. 1 Effect on Chl content Chlorophyll is an important structural and functional substance that absorbs sunlight and uses its energy to synthesize carbohydrates from C02 and water. Under adverse environmental conditions, the variation of chlorophyll content indicates a possible damage in the photosynthetic capacity of the chloroplasts. Fig. 1 ( a ) shows the dynamic changes of the Chl content in rape seedlings with six treatments for 5 d . For treatments TI and T2, the Chl content decreased continuously for the first 4 d , compared to CK, and the decrease in treatment T2 was more dramatic than that in treatment T I . Chl content in treatment TI began to increase on the 4th day. It suggested that rape seedlings might bear the damage by this intensity of UV-B radiation, which would be restored gradually because of light-repairL6]. On the contrary, Chl content in treatment T2 decreased continuously until the end of the experiment. This phenomenon showed that the injury caused by this intensity of UV-B radiation to the chloroplasts could not be restoredr7]. For treatment of Ce, Chl content kept its own balance, all the time higher than that of CK. The variation of Chl content in treatment Ce + TI was similar to that in treatment T I , but the decrease rate of the former was obviously smaller and the light-repair came 3 d earlier. It is demonstrated that Ce effectively promotes the potential ability of plants for restoration, and alleviated the damage of UV-B radiation. In the same way, the variation of Chl content in treatment Ce + T2 is similar to that in treatment T2with the exception that the decrease rate of the former is smaller than that of the latter. Furthermore, analysis of the difference in Chl content between treatments Ce + T, and Ce + T2 show that Ce has a more prominently protective effect on the rape seedlings exposed to the TI level rather than the T2 level of UV-B radiation. 2 . 1 . 2 Effect on membrane permeability Membrane permeability ( E % ) is used as an index of lipid peroxidation in plants under adverse environmental conditions. Compared to CK , membrane permeabilities in treatments TI and T2 were both increased, and the increase rate of the latter was larger. Moreover,
.
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are shown in Fig. 2 ( a ) . For both treatments TI and T2, SOD activities increased initially and then de-
membrane permeability in the TI treatment was increased initially and then decreased, close to CK. Analysis of this changing tendency indicated that the startup of radical defense systems induced by oxidative stress helped to scavenge productive free radicals because of UV-B radiation, and therefore lightened the damage on the membrane. However, membrane permeability in treatment T2 increased continuously, with a tendency toward overall collapse. It suggested that the excessive radicals induced by the T2 level of UV-B went beyond the range of the radical scavenging capacity of defense systems, the damage on membrane was even worse. For treatment of Ce, membrane permeability was lower than that of CK, on account of Ce scavenging radicals and maintaining membrane stability[*]. The variation of membrane permeability in treatment Ce + T, was similar to that in treatment T I , whereas, the increase of the former was far smaller and the restoration of the former occurred earlier. In the same way, the variation of membrane permeability in treatment Ce + T2 was also similar to that of treatment T2with the exception that the extent of increase of the former was smaller. These results prove that Ce is capable of improving the radical scavenging capacity of defense enzymes, enhancing the stability of the membrane, and consequently postponing the collapse of the membrane structure under UV-B radiation (Fig. 1( b ) ) .
creased, whereas the increase rate was larger and the peak value occurred later in treatment T2. It was demonstrated that there was a correlation between the irritability of SOD and stress intensities, and the postponement of the peak value might be related to the adaptive response of SOD activity to T2 level of UV-B radiation. It was presumed that, in the two abovementioned treatments during the late phase of the experiment (Figs. 1 ( b ) and 2( a ) ) , the decrease of SOD activity in the TI treatment was related to a small quantity of the *02accumulation induced by the low intensity of stress, and that in the T2treatment was on account of excessive so2-accumulation leading to the passivity of enzyme, and excessive O2- accumulation was also the main cause of the damaged cell membrane[*]. For Ce treatment, SOD activity was higher than that of CK, being activated by Ce . Compared to the TI treatment, the SOD activity in the Ce + TI treatment was higher in the early phase, and the time taken to approach the CK level was earlier, because it was activated by Ce scavenging and promptly * 02-was induced by oxidatiwe stress. Similarly, the SOD activity in the Ce + T2 treatment was also higher uhan that in the T2 treatment in the early phase, being activated by Ce as well as induced by free radicals, and subsequently decreased to the latter level on account of the damage aggravated and the balance between radical generation and elimination disturbed. Analysis of the differences between treatments Ce + TI and Ce + T3 indicate that there is a correlation between the regulating effect of Ce on the SOD activity under UV-B radiation and the intensity of UV-B radiation. 2 . 2 . 2 Effect on CAT As the second defense line against radicals, CAT is an enzyme that accelerates the decomposition of H2 O2 , as well as prevents the
2.2 Effect of Ce on antioxidant enzymes in rape seedlings under UV-B radiation 2 . 2 . 1 Effect on SOD Superoxide dismutase (SOD), as the first defense line against radicals, are a group of enzymes that accelerate the conversion of ' 0 2 - to H 2 0 2 , and can prevent initially the generation of 02- and OH that induce the lipid peroxidation and the degradation of a variety of important biological molecules such as nucleic acids, proteins etc. The changes of the SOD activity with different treatments
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Effect of Ce on Chl content and membrane permeability in rape seedlings under UV-B radiation ( a ) Chlorophyll content; (b) Membrane permeability +-CK; -.-Ce ; -A-T, ; -A-T* ; - * -Ce + T,; -u-Ce + T2
Liang C J et a1 . Effect of Cerium on Antioxidant Defense System in Rape Seedlings
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Effect of Ce on activities of SOD, CAT, and POD in rape seedlings under UV-B radiation ( a ) SOD activity; (b) CAT activity; ( c ) POD activity +-CK ; -.-Ce ; -a-TI ; -r-T2 ; - * -Ce + TI; -O-Ce + Tz
Haber-Weiss reaction ( * 0 2 + H 2 0 2 - s OH + OH + 0,) from generating * OH. Consequently, the degradation of chlorophyll accelerated by OH may be avoided. For treatments TI and T2, CAT activities were both initially increased and then decreased, whereas the variation rate of the former was smaller than that of the latter. In addition, the causes of such a change were varied in the two treatments. The initial increase of CAT in the TI treatment was because of the irritability of CAT to oxidative stress, and the decrease was on account of the reduction in H202 accumulation resulting from the radical scavenging capacity of CAT promoted, For the T2 treatment, the increase in CAT activity was also related to the irritability of CAT to oxidative stress, whereas the decrease might have resulted from the suppressive effect of excessive H202 accumulation. CAT activity in Ce treatment was higher than that in CK, being attributed to Ce accelerating the enzyme activity. Compared to the TI treatment, the variation of CAT activity in the Ce + TI treatment was similar, but the increase rate of the former was larger and the peak value occurred earlier. Such results might be attributed to the regulation of Ce and induction of H 2 0 2 . In the same way, the variation of CAT in treatments Ce + T2 and T2 was alike, with the exception that the increased extent of the former initially was larger and showed no tendency of decrease. The explanation of the above phenomenon is that Ce has a stimulative effect on CAT activity, and CAT is less sensitive than SOD to adverse environmental conditions (Fig. 2( b ) ) . 2.2. 3 Effect on POD Peroxidase (POD) is a group of enzymes that scavenge organic and inorganic peroxides. Compared to CK, POD activity was increased by supplementary UV-B radiation, and the increase rate was related to the intensity of UV-B radiation. The phenomenon that POD activity in TI treatment increased initially and decreased to CK level
might be the adaptive response of POD to the fluctuation of radical accumulation. Differing from the TI treatment, POD activity in the T2 treatment was increased throughout the experiment. The increase initially was because of the irritability of POD to radicals induced by adverse stress, and subsequently resulted from POD participating in the process of lipid peroxidation and cell senescence. For the Ce treatment, POD activity increased placidly because of Ce regulation. The variation of POD activity in Ce + T, treatment was similar to that in the TI treatment except that the time for POD activity of the former decreasing to the CK level was earlier. It suggested that Ce not only regulated POD activity, but also effectively eliminated radicals. Similarly, the variation of POD in treatments Ce + T2 and T2 was alike. The only difference was that the POD activity in the former w a s obviously higher than that in the latter, in the late phase, which indicated that the defense function of POD was enhanced by Ce in the early phase and abated gradually in the late phase on account of the damage of radicals worsened by high (T2) intensity of UV-B radiation, and finally POD joined in the process of cell senescence. Remarkably, there is a significant difference between SOD, CAT, and POD, that is, POD is a defense enzyme which scavenges radicals, and also participates in the process of cell senescence (Fig. 2( c ) ) .
3 Conclusions 1. Under UV-B radiation, rape seedlings have light-repair capacity for repairing the damage on chlorophyll and membrane structure, and that the restoring course and extent are both dependent on the intensity of UV-B radiation. 2 . On account of Ce participation, the course of light-repair in chlorophyll and membrane permeability is shortened and the changing rate of each phase decreased. 3 . For UV-B treatment, the time sequence of the
JOURNAL OF RARE EARTHS, Vol. 2 4 , N o . 3 , Jun . 2006
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defense enzymes' peak value is SOD ( 2 , 3 d ) < CAT (3, 4 d ) < POD(4, 5 d ) . It indicates that there is a difference among the sensibility of the three enzymes to UV-B radiation, and the sensibility sequence is SOD, CAT, and POD. 4. The differences in variation of SOD, CAT, and POD, between treatments Ce + UV-B and UV-B are in the activity of the three enzymes, the former is higher in the early phase, and the peak value of the former occurs earlier. This phenomenon shows that Ce is capable of effectively enhancing the ability of the three enzymes to scavenge free radicals, consequently alleviating the injury of radicals to the membrane system. Noticeably, under the T2 level of UV-B radiation, when the regulation of Ce on the POD activity is disabled, the function of POD is conversed from scavenging radicals to accelerating cell senescence (Figs. 2 ( c ) and l ( b ) ) . 5 . The protective effect of Ce on the membrane under UV-B radiation builds on regulating defense enzymes, and the regulating effect is related to UV-B intensity. In this study, it showed that the regulating effect of Ce on defense enzymes under the T, level of UV-B radiation is superior to that under the T2 level. From the above results, it can be deduced that the application of Ce on regulating defense enzyme activities and maintaining membrane stability can improve the resistance of crops to UV-B radiation.
feet of rare earths on plant under elevated ultraviolet-B radiation stress: I Effect of cerium on growth and photosynthesis in rape seedlings exposed to elevated ultraviolet-B radiation [ J 1. Journal of Rare Earths, 2005, 23 ( 5 ) : 569. Hernan C , Susana M G , Maria L T . Effect of UV-B radiation on antioxidant defense system in sunflower cotyledons [ J ] . Plant Science, 2002, 162: 939. Murphy T M . Membrane as targets of ultraviolet-B radiation [ J ] . Physiol. Plant, 1983, 58(2): 381. Zhang Zhiliang. Guide to Experiments of Plants Physiology (in Chin. ) [ M ] , Beijing: High Educational Press, 1990. 88. Zou Qi. Guide to Experiments of Plants Physiology and BiochemistIy (in Chin. ) [ M] . Beijing: China Agriculture Press, 1997. 77. Liu Qinghua, Zhong Zhangcheng . Effects of ultravioletB radiation on photosynthetic physiology parameters of Ginkgo biloba [ J ] . Journal of Southwest China Normal University ( Natural Science, in Chin. ) , 2002, 27 ( 3 : 378. Zhou Qing , Huang Xiaohua, Zhang Guangsheng , et a1 . Advances of recent research on rare earth in the field of pollution ecology [ J ] . Journal of Rare Earths, 2004, 22 (2): 177. Jiang Mingyi, Yang Wenying, Xu Jiang, et al. Active oxygen damage effect of chlorophyll degradation in rice seedlings under osmotic stress [ J ] . Acta Botanica Sinica (in Chin. ) , 1994, 36( 4) : 289. Tanaka K , Suda Y , Kondo N , et al. O3 tolerance and the ascorbate-dependent HzOzdecomposing system in chloroplasts [J] . Plant Cell Physiol, , 1985, 26(7) : 1425.
References : [ 11 Liang Chanjuan , Huang Xiaohua, Tao Wenyi , et al ,
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Induction of Volatile Organic Compounds in Leaves of Lycopersicon Esculentum by Nd3 He Peiqing' , Chen Kaoshan''2* , Tian Li''3, Li Guangyou2( 1 . First Znstitute of Oceanography, SOA , Qingdao 266061 , China ; 2 . School of Lqe Science , Shandong University, Jinan 250100, China ; 3 . Qingdao University of Science and Technology , Qingdao 266042 , China ) +
Abstract: The effects of Nd3+ on the quality and quantity of volatile organic compounds (VOCs) in the leaves of Lycopersicon esculentum were studied. The results demonstrate that Nd3' can increase the total amount of VOC by 75 % after treatment for 120 h , as compared with the control. Phyto-oxylipins , terpenoids and aromatic compounds were increased by 73 % , 38 % and 2 1 % , respectively. ( E ) -2-hexenal , the most abundant constituent is increased by 7 4 % , pphellandrene and a-caryophyllene in terpenoids , euKey words : Nd3
+
; Lycopersicon esculewum ; volatile
genol in aromatic compounds are also enhanced significantly, and increase by 1 2 9 % , 65% and 3 0 9 % , respectively. Nd3' in different concentration can increase the production of VOCs and shows different trends in the time course of induction. There is also an increase in 0; formation, chitinase and p-1,3-glucanase activities in response to Nd" treatment. These findings suggest that Nd3' may act as a potent agent to enhance the ability of L . esculentum against disease by increasing the production of VOCs .
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organic compounds ; 0;; chitinase ; p- 1 ,3-glucanase ; rare earths (See J . Chin. RE. Soc. (in C h i n . ) , 2006, 24(3): 338 for full text)
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JOURNAL OF DIRECT.
JOURNAL OF RAKE EAKTHS 24 (2006) 364 - 368
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Effect of Rare Earths on Plants under Supplementary Ultraviolet-B Radiation: 1 Effect of Cerium on Antioxidant Defense System in Rape
.
Seedlings under Supplementary Ultraviolet-B Radiation Liang Chanjuan (LWB)',Huang Xiaohua (*&+)', Tao Wenyi (psISt#)', Zhou Qing (PI * ) I * ( 1 . The Key Laboratory of Industrial Biotechnology , Ministry of Education, Wuxi 214036, China ; 2 . College of Chemistry & Environmental Science , Nanjing Normal University , Nanjing 210097, China ) Received 10 June 2005; revised 26 August 2005
Abstract: Effects of cerium ( Ce3 ) on membranous protective enzymes in rape seedlings exposed to two levels of enhanced ultraviolet-B radiation (UV-B , 280 320 nm) were studied by hydroponics in the laboratory. The results show that the chlorophyll content decreases and membrane permeability increases in the leaves under UV-B irradiation with an intensity of 0.15 and 0.35 W.m-2. The activities of SOD, CAT and POD are first increased and then decreased in leaves exposed to a low level of UV-B radiation. POD activity in leaves exposed to a high level of UV-B radiation is enhanced constantly. The sensitivities of these enzymes to UV-B radiation are SOD > CAT > POD. The injury by UV-B radiation on the functions of protective enzymes is lightened, their ability to scavenge radicals is improved, and the membrane permeability is maintained by Ce . Furthermore, the protective effect of cerium is more obvious in plants exposed to low levels of UV-B radiation than to high levels of it. Accordingly, all results prove that the protective effect of Ce on plants under UV-B radiation is realized through the protective system of plants. +
-
Key words : cerium ; elevated UV-B radiation ; rape seedlings ; protective enzymes ; membrane permeability ; rare earths Document code: A CLC number: 0614.3 Article ID: 1002 - 0721(2006)03 - 0364 - 05
The increase in ground level ultraviolet-B radiation (UV-B, 280 320 nm) as a result of stratospheric ozone depletion may have major deleterious effects on crop photosynthesis and production. As one major environmental problem, it has attracted more and more attention of researchers, and therefore there have been substantive and timely reports, providing abundant information about the damage of UV-B radiation on crops. However, the studies about the ecological protection of plants against damage of UV-B radiation are comparatively few. We have previously reported that Ce can alleviate the suppressive effect of
-
supplementary UV-B radiation on growth and photosynthesis in rape seedlings"]. In addition, it is clear to us that the improvement of photosynthetic function in leaves with Ce treatment is one of the direct causes preventing rape seedlings worsening under UV-B radiation. The supplementary UV-B radiation induces overproduction of free radicals and results in oxidation of lipids in plant tissues as reported by Hernan"]. Furthermore, the decrease in biomass is closely related to the breakage of the cell membrane in plant tissues, because of the damage of UV-B radiationL3'. Consequently, it is necessary to assess the effect of Ce on
* Corresponding author (E-mail : zhouqeco@yahoo. com .cn ) Foundation item: Project supported by the National Natural Science Foundation of China (30570323. 20471030) and the Foundation of State Planning Committee (IFZ20051210)
Biography: Gang Chanjuan (1978 - 1, Female, Doctor candidate Copyright 0 2 0 0 6 , by Editorial Committee of Journal of the Chinese Rare Earths Society. Published by Elsevier B .V . All rights reserved
Liang C J et a1 . Effect of Cerium on Antioxidant Defense System in Rape Seedlings
the antioxidant enzyme system in plants under supplementary UV-B radiation. On the basis of earlier investigations, considering the antioxidant enzymes scavenging free radical as the research objects, we investigated the irritability response of these enzymes, including Superoxide dismutase ( SOD ), catalase (CAT), and peroxidase (POD) to UV-B radiation, as well as the regulation of Ce on them under such adverse stress.
1 Materials and Methods 1.1 Plant culture The rape ( Brmsica juncea L . ) seeds of “Shilifeng ” were sterilized and cultured according to Ref. [ 11.
1.2 Treatments The optimum concentration of the CeC13 solution was 12 mg.L-l, which was determined in the pre-experiments. The CeC13 solution was sprayed evenly on the leaves until drops began to fall. The same amount of distilled water was applied for CK . After 48 h , half of the seedlings pretreated with Ce were placed under ultraviolet lamps. Enhanced UV-B radiation was performed with 40 W UV-B lamps, produced by Nanjing Lamp Factory, hanged perpendicularly over the plants. The levels of UV-B radiation were 0.15 and 0.35 W m2, which were measured with an ultraviolet radiometer, made by photo-electricity instrument factory of the Beijing Normal University. Seedlings were irradiated for 5 h from 1O:OO to 15:00, for a total of 6 d . The height of the lamps over the plants was adjusted to maintain consistent radiation intensity. There were 6 sample sets in the present experiment: controls (sprayed with deionized water), Ce (sprayed with CeC13 solution ) , TI ( irradiated with 0.15 W*rn-’ UV-B), T2(Irradiated with 0.35 UV-B) , Ce + TI(sprayed with CeC13 solution and then exposed to 0.15 UV-B radiation), and Ce + T2( sprayed with CeC13 solution and then exposed to 0.35 W m-’ UV-B radiation). There were 3 replicates for each set and 3 pots per treatment.
1.3 Determination The physiological indices were measured at 1O:OO every day for a total of 5 d after the treatments with Ce and UV-B radiation were finished. Total chlorophyll content (Chl content) , Cell membrane permeability ( E % ) , and POD activity were determined according to Ref. [ 41 . CAT activity was measured with
365
the method described in Ref. [ 5 1 . SOD activity was measured with the reagent box produced by Nanjing Jiancheng Bioengineering Institute.
2 Results and Discussion 2.1
Effect of Ce on chlorophyll content and membrane permeability in rape seedlings under W - B radiation
2.1. 1 Effect on Chl content Chlorophyll is an important structural and functional substance that absorbs sunlight and uses its energy to synthesize carbohydrates from C02 and water. Under adverse environmental conditions, the variation of chlorophyll content indicates a possible damage in the photosynthetic capacity of the chloroplasts. Fig. 1 ( a ) shows the dynamic changes of the Chl content in rape seedlings with six treatments for 5 d . For treatments TI and T2, the Chl content decreased continuously for the first 4 d , compared to CK, and the decrease in treatment T2 was more dramatic than that in treatment T I . Chl content in treatment TI began to increase on the 4th day. It suggested that rape seedlings might bear the damage by this intensity of UV-B radiation, which would be restored gradually because of light-repairL6]. On the contrary, Chl content in treatment T2 decreased continuously until the end of the experiment. This phenomenon showed that the injury caused by this intensity of UV-B radiation to the chloroplasts could not be restoredr7]. For treatment of Ce, Chl content kept its own balance, all the time higher than that of CK. The variation of Chl content in treatment Ce + TI was similar to that in treatment T I , but the decrease rate of the former was obviously smaller and the light-repair came 3 d earlier. It is demonstrated that Ce effectively promotes the potential ability of plants for restoration, and alleviated the damage of UV-B radiation. In the same way, the variation of Chl content in treatment Ce + T2 is similar to that in treatment T2with the exception that the decrease rate of the former is smaller than that of the latter. Furthermore, analysis of the difference in Chl content between treatments Ce + T, and Ce + T2 show that Ce has a more prominently protective effect on the rape seedlings exposed to the TI level rather than the T2 level of UV-B radiation. 2 . 1 . 2 Effect on membrane permeability Membrane permeability ( E % ) is used as an index of lipid peroxidation in plants under adverse environmental conditions. Compared to CK , membrane permeabilities in treatments TI and T2 were both increased, and the increase rate of the latter was larger. Moreover,
.
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are shown in Fig. 2 ( a ) . For both treatments TI and T2, SOD activities increased initially and then de-
membrane permeability in the TI treatment was increased initially and then decreased, close to CK. Analysis of this changing tendency indicated that the startup of radical defense systems induced by oxidative stress helped to scavenge productive free radicals because of UV-B radiation, and therefore lightened the damage on the membrane. However, membrane permeability in treatment T2 increased continuously, with a tendency toward overall collapse. It suggested that the excessive radicals induced by the T2 level of UV-B went beyond the range of the radical scavenging capacity of defense systems, the damage on membrane was even worse. For treatment of Ce, membrane permeability was lower than that of CK, on account of Ce scavenging radicals and maintaining membrane stability[*]. The variation of membrane permeability in treatment Ce + T, was similar to that in treatment T I , whereas, the increase of the former was far smaller and the restoration of the former occurred earlier. In the same way, the variation of membrane permeability in treatment Ce + T2 was also similar to that of treatment T2with the exception that the extent of increase of the former was smaller. These results prove that Ce is capable of improving the radical scavenging capacity of defense enzymes, enhancing the stability of the membrane, and consequently postponing the collapse of the membrane structure under UV-B radiation (Fig. 1( b ) ) .
creased, whereas the increase rate was larger and the peak value occurred later in treatment T2. It was demonstrated that there was a correlation between the irritability of SOD and stress intensities, and the postponement of the peak value might be related to the adaptive response of SOD activity to T2 level of UV-B radiation. It was presumed that, in the two abovementioned treatments during the late phase of the experiment (Figs. 1 ( b ) and 2( a ) ) , the decrease of SOD activity in the TI treatment was related to a small quantity of the *02accumulation induced by the low intensity of stress, and that in the T2treatment was on account of excessive so2-accumulation leading to the passivity of enzyme, and excessive O2- accumulation was also the main cause of the damaged cell membrane[*]. For Ce treatment, SOD activity was higher than that of CK, being activated by Ce . Compared to the TI treatment, the SOD activity in the Ce + TI treatment was higher in the early phase, and the time taken to approach the CK level was earlier, because it was activated by Ce scavenging and promptly * 02-was induced by oxidatiwe stress. Similarly, the SOD activity in the Ce + T2 treatment was also higher uhan that in the T2 treatment in the early phase, being activated by Ce as well as induced by free radicals, and subsequently decreased to the latter level on account of the damage aggravated and the balance between radical generation and elimination disturbed. Analysis of the differences between treatments Ce + TI and Ce + T3 indicate that there is a correlation between the regulating effect of Ce on the SOD activity under UV-B radiation and the intensity of UV-B radiation. 2 . 2 . 2 Effect on CAT As the second defense line against radicals, CAT is an enzyme that accelerates the decomposition of H2 O2 , as well as prevents the
2.2 Effect of Ce on antioxidant enzymes in rape seedlings under UV-B radiation 2 . 2 . 1 Effect on SOD Superoxide dismutase (SOD), as the first defense line against radicals, are a group of enzymes that accelerate the conversion of ' 0 2 - to H 2 0 2 , and can prevent initially the generation of 02- and OH that induce the lipid peroxidation and the degradation of a variety of important biological molecules such as nucleic acids, proteins etc. The changes of the SOD activity with different treatments
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Effect of Ce on Chl content and membrane permeability in rape seedlings under UV-B radiation ( a ) Chlorophyll content; (b) Membrane permeability +-CK; -.-Ce ; -A-T, ; -A-T* ; - * -Ce + T,; -u-Ce + T2
Liang C J et a1 . Effect of Cerium on Antioxidant Defense System in Rape Seedlings
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Effect of Ce on activities of SOD, CAT, and POD in rape seedlings under UV-B radiation ( a ) SOD activity; (b) CAT activity; ( c ) POD activity +-CK ; -.-Ce ; -a-TI ; -r-T2 ; - * -Ce + TI; -O-Ce + Tz
Haber-Weiss reaction ( * 0 2 + H 2 0 2 - s OH + OH + 0,) from generating * OH. Consequently, the degradation of chlorophyll accelerated by OH may be avoided. For treatments TI and T2, CAT activities were both initially increased and then decreased, whereas the variation rate of the former was smaller than that of the latter. In addition, the causes of such a change were varied in the two treatments. The initial increase of CAT in the TI treatment was because of the irritability of CAT to oxidative stress, and the decrease was on account of the reduction in H202 accumulation resulting from the radical scavenging capacity of CAT promoted, For the T2 treatment, the increase in CAT activity was also related to the irritability of CAT to oxidative stress, whereas the decrease might have resulted from the suppressive effect of excessive H202 accumulation. CAT activity in Ce treatment was higher than that in CK, being attributed to Ce accelerating the enzyme activity. Compared to the TI treatment, the variation of CAT activity in the Ce + TI treatment was similar, but the increase rate of the former was larger and the peak value occurred earlier. Such results might be attributed to the regulation of Ce and induction of H 2 0 2 . In the same way, the variation of CAT in treatments Ce + T2 and T2 was alike, with the exception that the increased extent of the former initially was larger and showed no tendency of decrease. The explanation of the above phenomenon is that Ce has a stimulative effect on CAT activity, and CAT is less sensitive than SOD to adverse environmental conditions (Fig. 2( b ) ) . 2.2. 3 Effect on POD Peroxidase (POD) is a group of enzymes that scavenge organic and inorganic peroxides. Compared to CK, POD activity was increased by supplementary UV-B radiation, and the increase rate was related to the intensity of UV-B radiation. The phenomenon that POD activity in TI treatment increased initially and decreased to CK level
might be the adaptive response of POD to the fluctuation of radical accumulation. Differing from the TI treatment, POD activity in the T2 treatment was increased throughout the experiment. The increase initially was because of the irritability of POD to radicals induced by adverse stress, and subsequently resulted from POD participating in the process of lipid peroxidation and cell senescence. For the Ce treatment, POD activity increased placidly because of Ce regulation. The variation of POD activity in Ce + T, treatment was similar to that in the TI treatment except that the time for POD activity of the former decreasing to the CK level was earlier. It suggested that Ce not only regulated POD activity, but also effectively eliminated radicals. Similarly, the variation of POD in treatments Ce + T2 and T2 was alike. The only difference was that the POD activity in the former w a s obviously higher than that in the latter, in the late phase, which indicated that the defense function of POD was enhanced by Ce in the early phase and abated gradually in the late phase on account of the damage of radicals worsened by high (T2) intensity of UV-B radiation, and finally POD joined in the process of cell senescence. Remarkably, there is a significant difference between SOD, CAT, and POD, that is, POD is a defense enzyme which scavenges radicals, and also participates in the process of cell senescence (Fig. 2( c ) ) .
3 Conclusions 1. Under UV-B radiation, rape seedlings have light-repair capacity for repairing the damage on chlorophyll and membrane structure, and that the restoring course and extent are both dependent on the intensity of UV-B radiation. 2 . On account of Ce participation, the course of light-repair in chlorophyll and membrane permeability is shortened and the changing rate of each phase decreased. 3 . For UV-B treatment, the time sequence of the
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defense enzymes' peak value is SOD ( 2 , 3 d ) < CAT (3, 4 d ) < POD(4, 5 d ) . It indicates that there is a difference among the sensibility of the three enzymes to UV-B radiation, and the sensibility sequence is SOD, CAT, and POD. 4. The differences in variation of SOD, CAT, and POD, between treatments Ce + UV-B and UV-B are in the activity of the three enzymes, the former is higher in the early phase, and the peak value of the former occurs earlier. This phenomenon shows that Ce is capable of effectively enhancing the ability of the three enzymes to scavenge free radicals, consequently alleviating the injury of radicals to the membrane system. Noticeably, under the T2 level of UV-B radiation, when the regulation of Ce on the POD activity is disabled, the function of POD is conversed from scavenging radicals to accelerating cell senescence (Figs. 2 ( c ) and l ( b ) ) . 5 . The protective effect of Ce on the membrane under UV-B radiation builds on regulating defense enzymes, and the regulating effect is related to UV-B intensity. In this study, it showed that the regulating effect of Ce on defense enzymes under the T, level of UV-B radiation is superior to that under the T2 level. From the above results, it can be deduced that the application of Ce on regulating defense enzyme activities and maintaining membrane stability can improve the resistance of crops to UV-B radiation.
feet of rare earths on plant under elevated ultraviolet-B radiation stress: I Effect of cerium on growth and photosynthesis in rape seedlings exposed to elevated ultraviolet-B radiation [ J 1. Journal of Rare Earths, 2005, 23 ( 5 ) : 569. Hernan C , Susana M G , Maria L T . Effect of UV-B radiation on antioxidant defense system in sunflower cotyledons [ J ] . Plant Science, 2002, 162: 939. Murphy T M . Membrane as targets of ultraviolet-B radiation [ J ] . Physiol. Plant, 1983, 58(2): 381. Zhang Zhiliang. Guide to Experiments of Plants Physiology (in Chin. ) [ M ] , Beijing: High Educational Press, 1990. 88. Zou Qi. Guide to Experiments of Plants Physiology and BiochemistIy (in Chin. ) [ M] . Beijing: China Agriculture Press, 1997. 77. Liu Qinghua, Zhong Zhangcheng . Effects of ultravioletB radiation on photosynthetic physiology parameters of Ginkgo biloba [ J ] . Journal of Southwest China Normal University ( Natural Science, in Chin. ) , 2002, 27 ( 3 : 378. Zhou Qing , Huang Xiaohua, Zhang Guangsheng , et a1 . Advances of recent research on rare earth in the field of pollution ecology [ J ] . Journal of Rare Earths, 2004, 22 (2): 177. Jiang Mingyi, Yang Wenying, Xu Jiang, et al. Active oxygen damage effect of chlorophyll degradation in rice seedlings under osmotic stress [ J ] . Acta Botanica Sinica (in Chin. ) , 1994, 36( 4) : 289. Tanaka K , Suda Y , Kondo N , et al. O3 tolerance and the ascorbate-dependent HzOzdecomposing system in chloroplasts [J] . Plant Cell Physiol, , 1985, 26(7) : 1425.
References : [ 11 Liang Chanjuan , Huang Xiaohua, Tao Wenyi , et al ,
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Induction of Volatile Organic Compounds in Leaves of Lycopersicon Esculentum by Nd3 He Peiqing' , Chen Kaoshan''2* , Tian Li''3, Li Guangyou2( 1 . First Znstitute of Oceanography, SOA , Qingdao 266061 , China ; 2 . School of Lqe Science , Shandong University, Jinan 250100, China ; 3 . Qingdao University of Science and Technology , Qingdao 266042 , China ) +
Abstract: The effects of Nd3+ on the quality and quantity of volatile organic compounds (VOCs) in the leaves of Lycopersicon esculentum were studied. The results demonstrate that Nd3' can increase the total amount of VOC by 75 % after treatment for 120 h , as compared with the control. Phyto-oxylipins , terpenoids and aromatic compounds were increased by 73 % , 38 % and 2 1 % , respectively. ( E ) -2-hexenal , the most abundant constituent is increased by 7 4 % , pphellandrene and a-caryophyllene in terpenoids , euKey words : Nd3
+
; Lycopersicon esculewum ; volatile
genol in aromatic compounds are also enhanced significantly, and increase by 1 2 9 % , 65% and 3 0 9 % , respectively. Nd3' in different concentration can increase the production of VOCs and shows different trends in the time course of induction. There is also an increase in 0; formation, chitinase and p-1,3-glucanase activities in response to Nd" treatment. These findings suggest that Nd3' may act as a potent agent to enhance the ability of L . esculentum against disease by increasing the production of VOCs .
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organic compounds ; 0;; chitinase ; p- 1 ,3-glucanase ; rare earths (See J . Chin. RE. Soc. (in C h i n . ) , 2006, 24(3): 338 for full text)