论文部分内容阅读
Abstract With Sunflower （Helianthus annuus L.） as an experimental material， phytohormones were externally applied， so as to screen phytohormones capable of alleviating environmental stress. Three kinds of phytohormones （auxin IAA， gibberellin GA and salicylic acid SA） were added through pot culture. The results showed that the three phytohormones all improved the accumulation of 88Sr in sunflower plant， and increased the translocation and bioaccumulation factors of 88Sr； and under the 100 mg/LSA treatment， the adsorption capacity， TF and BCF of 88Sr in sunflower plant reached the highest values.
Key words Plant hormone； Phytoremediation； Translocation
Sr is widely distributed in nature. Radioactive 90Sr is strongly soluble in water， and has chemical properties similar to Ca element[1]， with a half life as long as 28.5 years. Radioactive Sr settling in soil could enter plant through the adsorption function of the root system， and then enter human body through food chain， causing potential internal irradiation hazard[2]. Therefore， it is urgent to govern Sr pollution. Zhu et al.[3] reported that the absorption capacities of plants in different families to 90Sr were in order of Cucurbitaceae > Urticaceae > Amaranthaceae > Solanaceae > Moraceae>Leguminosae > Graminaceae. Phytoremediation applying the adsorption and translocation of plant to nuclide to govern pollution has become one of the main means for controlling pollution， while one of the effective measures for improving its remediation efficiency is the addition of phytohormones. Wen et al.[4] treated pyrethrum with 625 mg/L auxin， and the results showed that each indicator reached the significant level. Many research results showed that phytohormones could remit the phytotoxicity of heavy metal nuclide， increase plant biomass and promote plant growth and development.
Materials and Methods
Experimental materials
Sunflower （Helianthus annuus L.）， also known as Kuihuazi， belongs to Helianthus in Compositae family of Asterales. It is an annual herb， native to North America， and grows well in warm areas. The plant could grow in all four seasons， mainly in summer and winter. Sunflower is a Sr and Cs hyperaccumulator with large biomass and strong nuclide accumulation capacity. It is adaptive to the southwest of Shandong Province.
Experiment methods
Plant cultivation and experimental treatments The experiment was carried out by pot culture， in Heze University， which has a warm temperate continental monsoon climate with an annual average precipitation of 660 mm. 88Sr was applied in the manner of Sr（NO3）2 with a concentration of 20 mg/kg. The three kinds of phytohormones （auxin IAA， gibberellin GA and salicylic acid SA） all had three treatment concentrations， as shown in Table 1. Sr（NO3）2 and phytohormones were all analytical reagents.
The seeds were sown on March 19， 2015， and seedlings were raised in open field. On April 21， when the plants had 4-6 leaves， three plants were planted in each plot， which had a diameter of 30 cm and a height of 23 cm， and filled with 6 kg of soil. 88Sr was mixed uniformly into soil in the form of water solution. The seedlings were planted in the soil added with 88Sr， which was prepared into water solutions with different concentrations according to different treatments. The seedlings were raised for 1 month then. On May 21， they were subjected to hormone treatment， in which the three hormones （IAA， GA3 and SA） were prepared into water solutions. Each hormone was designed with three concentrations （Table 1）， and nine hormone treatments were formed. One clear water treatment was also set as control （CK）， and there were thus 10 treatments in total. Each treatment has three replications， and included nine plants， and there were 90 plants in total.
Determination of sunflower biomass The harvested sunflower was cleaned with deionized water and drained. The root， stem and leaf were separated， followed by deactivation of enzymes at 105 ?? for 30 min， and oven??drying at 70 ?? to constant weight （for about 48 h）.The various parts were weighed， respectively.
Determination of??88Sr content The oven??dried plant samples were ground， and a certain amount of each sample （0.2 g） was added into a triangular flask， added with a certain amount of mixed acid （nitric acid?? perchloric acid= 3?? 1， 10 ml）， and stood overnight with a cover. The sample solution was poured into a Kjeldahl flask， and digested on an electric furnace， until white smoke appeared and the solution was colorless and transparent. The solution was then diluted with 0.5 mol/L nitric acid to 100 ml. 88Sr contents in plant samples were determined by flame atomic absorption spectrometry， with an AA700 flame atomic absorption spectrophotometer produced by American PE company.
Translocation factor （TF）=Sr2+ content in various aboveground parts （mg/g）/Sr2+ content in root system （mg/g） [5]
Bioaccumulation factor （BCF）= Sr2+ content in the stem， leaf and root parts （mg/g）/Sr2+ content in culture medium or soil （mg/g）[6] Results and Analysis
Effect on sunflower biomass
The biomass of the root， stem， leaf and flower parts of sunflower under hormone treatment was determined， and the results are shown in Fig. 1.
It could be seen from Fig. 1 that the treatments with the three phytohormones significantly increased the biomass of the root， stem， leaf and flower parts of sunflower， with significant differences from the CK （P SA > GA， and the effects on the biomass of the stem， leaf and flower parts were in order of GA > SA > IAA. Under the 100 mg/L IAA treatment， the root biomass reached its maximum value， higher than the CK by 163.28%； and under the treatment of 500 mg/L gibberellin treatment， the biomass of the stem， leaf and flower part reached maximum values， which were 2.12， 1.83 and 1.93 times of the CK， respectively.
Accumulation characteristics of 88Sr in sunflower
Absorption of 88Sr by various organs of sunflower The 88Sr contents in the root， stem and leaf and flower parts of sunflower were determined under hormone treatment. The results are shown in Fig. 2.
It could be seen from Fig. 2 that under different hormone treatments， the 88Sr contents in various parts of sunflower were different， with significant differences from the CK， and generally higher than the CK. The effects of the three hormones on 88Sr contents in various parts were overall in order of SA > GA > IAA. Under the SA treatments， the 100 mg/L SA treatment showed the maximum values of 88Sr contents in various parts among all the treatments， which were higher than the CK by 97.21%， 108.45%， 70.42% and 77.66%， respectively.
Translocation characteristics of 88Sr in sunflower The TF values of 88Sr in the stem， leaf and flower parts under various hormone treatments are shown in Fig. 3. It could be seen from Fig. 3 that compared with the CK， the three phytohormones all improved the TFs of 88Sr. The TFs of 88Sr in the flower and leaf parts were significantly higher than that in the stem part， and the effects of the three hormones were overall in order of SA > GA > IAA.
It could be seen from Fig. 3 that the translocation factors of the stem part were all smaller than 1. Specifically， under the IAA1 treatment， the TF value was the smallest， without a significant difference from the CK， while the largest TF value appeared in the SA2 treatment， and the values were 1.09 and 1.48 times of the CK， respectively. The TF values of the leaf part were all larger 0.5. Specifically， the smallest value was observed in the IAA1 treatment， while the largest TF value appeared in the SA2 treatment. The TF values of the flower parts were generally higher than those of the stem part. Specifically， the IAA3 treatment exhibited the smallest TF value， which was not significantly different from the CK， while the largest value appeared in the SA2 treatment， and the values were 1.05 and 1.31 times of the CK， respectively. Accumulation of 88Sr in sunflower BCF values of 88Sr in various parts of sunflower were calculated according to the 88Sr contents in the root， stem， leaf and flower parts of sunflower and the 88Sr content in soil under plant hormone treatments， as shown in Fig. 4. It could be seen from Fig. 4 that the BCF values under various treatments were all larger than 1， and the three phytohormones all improved the BCF values of 88Sr， and the treatment effects of the three hormones overall ranked as SA > GA > IAA. The absorption capacity of the stem part to 88Sr was generally lower than other parts.
Discussion and Conclusions
The three phytohormones all improved the accumulation of 88Sr in sunflower plant， and increased the translocation and bioaccumulation factors of 88Sr， which were significantly higher than the CK. The optimal application concentrations of the three phytohormones （IAA， GA and SA） were 100， 500 and 100 mg/L， respectively. Under the 100 mg/LSA treatment， the adsorption capacity， TF and BCF of 88Sr in sunflower plant reached the highest values. This result accords with the research result obtained by Petr Soudek et al.[8]， who found that sunflower has a stronger 88Sr accumulation capacity. This might be because that phytohormones could improve the activity of atpase in cytomembrane and adjust the function of membrane proteins related to the translocation of metal elements， thereby helping metal elements to pass through cytomembrane and increasing its accumulation in cells[9]. Furthermore， Wang et al.[10] found that the external application of SA on Cassia tora could improve the absorption and accumulation of Al3+ in the root system of C. tora.
To sum up， rational application of plant hormone could reduce the adverse effects of pollutants to plant physiology， maintain normal growth and development of plant when alleviating stress， and facilitate the absorption， accumulation and translocation of pollution elements in plant.
References
[1] ZHANG QF. Phytoremediation of environment： Soil contamination and remediation[J]. Garden， 2010， 1（2）： 66-68.
[2] LI LH， ZHENG J， ZHANG C， et al. Effect investigation of strontium carbonate wastewater on ecological environment[J]. Chongqing Environmental Science， 2002， 24（2）： 63-64.
[3] ZHU YY， QIU TC. The behavior of fission products 90Sr， 137Cs and 144Ce in soil??plant system[J]. China Environmental Science， 1991， 11（4）： 266-269.
[4] MOHD I， SHIVENDRAVS. Promising role of plant hormones in translocation of lead in Sesbania drummondii shoots[J]. EnvironPollut， 2008， 15332（2）： 29-36. [5] ZHANG XX， WANG D， LI WF， et al. Studies on accumulation of 133Cs and 88Sr in Vicia faba Linn and irradiation damage effect[J]. Journal of Radiation Research and Radiation Processing， 2010， 28（1）： 48-52.
[6] WEN FP， WANG D， XU CH， et al. Uptake and distribution of 133Cs and 88Sr in sunflower[J]. Bulletin of Botanical Research， 2009， （5）： 592-596.
[7] ZHANG XX， WANG D， ZHONG MZ， et al. Response of Celosia cristata Linn to Cs and Sr stress and their accumulation characteristic[J]. Acta Agriculturae Nucleatae Sinica， 2010， 24（3）： 628-633.
[8] PETR S， SARKA V， ZUZANA V， et al. 137Cs and 90Sr uptake by sunflower cultivated underhydroponic conditions[J]. Journal of Environmental Radioactivity， 2006， 88： 236-250.
[9] PAZURKIEWICZK K， GALAS W， KITA A， et al. The effects of seleniumon the accumulation of some metals in Zea mays L. plants treated with indole??3??acetic acid[J]. Cellular??molecular Biology Letters， 2003， 8（1）： 97-103.
[10] WANG H， SHAN X， WEN B， et al. Effect of indole??3??acetic acid on lead accumulationin maize （Zea mays L.） seedlings and therelevant antioxidant response[J]. Environ. Exp. Bot， 2007， 61（1）： 246¨C253.
Key words Plant hormone； Phytoremediation； Translocation
Sr is widely distributed in nature. Radioactive 90Sr is strongly soluble in water， and has chemical properties similar to Ca element[1]， with a half life as long as 28.5 years. Radioactive Sr settling in soil could enter plant through the adsorption function of the root system， and then enter human body through food chain， causing potential internal irradiation hazard[2]. Therefore， it is urgent to govern Sr pollution. Zhu et al.[3] reported that the absorption capacities of plants in different families to 90Sr were in order of Cucurbitaceae > Urticaceae > Amaranthaceae > Solanaceae > Moraceae>Leguminosae > Graminaceae. Phytoremediation applying the adsorption and translocation of plant to nuclide to govern pollution has become one of the main means for controlling pollution， while one of the effective measures for improving its remediation efficiency is the addition of phytohormones. Wen et al.[4] treated pyrethrum with 625 mg/L auxin， and the results showed that each indicator reached the significant level. Many research results showed that phytohormones could remit the phytotoxicity of heavy metal nuclide， increase plant biomass and promote plant growth and development.
Materials and Methods
Experimental materials
Sunflower （Helianthus annuus L.）， also known as Kuihuazi， belongs to Helianthus in Compositae family of Asterales. It is an annual herb， native to North America， and grows well in warm areas. The plant could grow in all four seasons， mainly in summer and winter. Sunflower is a Sr and Cs hyperaccumulator with large biomass and strong nuclide accumulation capacity. It is adaptive to the southwest of Shandong Province.
Experiment methods
Plant cultivation and experimental treatments The experiment was carried out by pot culture， in Heze University， which has a warm temperate continental monsoon climate with an annual average precipitation of 660 mm. 88Sr was applied in the manner of Sr（NO3）2 with a concentration of 20 mg/kg. The three kinds of phytohormones （auxin IAA， gibberellin GA and salicylic acid SA） all had three treatment concentrations， as shown in Table 1. Sr（NO3）2 and phytohormones were all analytical reagents.
The seeds were sown on March 19， 2015， and seedlings were raised in open field. On April 21， when the plants had 4-6 leaves， three plants were planted in each plot， which had a diameter of 30 cm and a height of 23 cm， and filled with 6 kg of soil. 88Sr was mixed uniformly into soil in the form of water solution. The seedlings were planted in the soil added with 88Sr， which was prepared into water solutions with different concentrations according to different treatments. The seedlings were raised for 1 month then. On May 21， they were subjected to hormone treatment， in which the three hormones （IAA， GA3 and SA） were prepared into water solutions. Each hormone was designed with three concentrations （Table 1）， and nine hormone treatments were formed. One clear water treatment was also set as control （CK）， and there were thus 10 treatments in total. Each treatment has three replications， and included nine plants， and there were 90 plants in total.
Determination of sunflower biomass The harvested sunflower was cleaned with deionized water and drained. The root， stem and leaf were separated， followed by deactivation of enzymes at 105 ?? for 30 min， and oven??drying at 70 ?? to constant weight （for about 48 h）.The various parts were weighed， respectively.
Determination of??88Sr content The oven??dried plant samples were ground， and a certain amount of each sample （0.2 g） was added into a triangular flask， added with a certain amount of mixed acid （nitric acid?? perchloric acid= 3?? 1， 10 ml）， and stood overnight with a cover. The sample solution was poured into a Kjeldahl flask， and digested on an electric furnace， until white smoke appeared and the solution was colorless and transparent. The solution was then diluted with 0.5 mol/L nitric acid to 100 ml. 88Sr contents in plant samples were determined by flame atomic absorption spectrometry， with an AA700 flame atomic absorption spectrophotometer produced by American PE company.
Translocation factor （TF）=Sr2+ content in various aboveground parts （mg/g）/Sr2+ content in root system （mg/g） [5]
Bioaccumulation factor （BCF）= Sr2+ content in the stem， leaf and root parts （mg/g）/Sr2+ content in culture medium or soil （mg/g）[6] Results and Analysis
Effect on sunflower biomass
The biomass of the root， stem， leaf and flower parts of sunflower under hormone treatment was determined， and the results are shown in Fig. 1.
It could be seen from Fig. 1 that the treatments with the three phytohormones significantly increased the biomass of the root， stem， leaf and flower parts of sunflower， with significant differences from the CK （P SA > GA， and the effects on the biomass of the stem， leaf and flower parts were in order of GA > SA > IAA. Under the 100 mg/L IAA treatment， the root biomass reached its maximum value， higher than the CK by 163.28%； and under the treatment of 500 mg/L gibberellin treatment， the biomass of the stem， leaf and flower part reached maximum values， which were 2.12， 1.83 and 1.93 times of the CK， respectively.
Accumulation characteristics of 88Sr in sunflower
Absorption of 88Sr by various organs of sunflower The 88Sr contents in the root， stem and leaf and flower parts of sunflower were determined under hormone treatment. The results are shown in Fig. 2.
It could be seen from Fig. 2 that under different hormone treatments， the 88Sr contents in various parts of sunflower were different， with significant differences from the CK， and generally higher than the CK. The effects of the three hormones on 88Sr contents in various parts were overall in order of SA > GA > IAA. Under the SA treatments， the 100 mg/L SA treatment showed the maximum values of 88Sr contents in various parts among all the treatments， which were higher than the CK by 97.21%， 108.45%， 70.42% and 77.66%， respectively.
Translocation characteristics of 88Sr in sunflower The TF values of 88Sr in the stem， leaf and flower parts under various hormone treatments are shown in Fig. 3. It could be seen from Fig. 3 that compared with the CK， the three phytohormones all improved the TFs of 88Sr. The TFs of 88Sr in the flower and leaf parts were significantly higher than that in the stem part， and the effects of the three hormones were overall in order of SA > GA > IAA.
It could be seen from Fig. 3 that the translocation factors of the stem part were all smaller than 1. Specifically， under the IAA1 treatment， the TF value was the smallest， without a significant difference from the CK， while the largest TF value appeared in the SA2 treatment， and the values were 1.09 and 1.48 times of the CK， respectively. The TF values of the leaf part were all larger 0.5. Specifically， the smallest value was observed in the IAA1 treatment， while the largest TF value appeared in the SA2 treatment. The TF values of the flower parts were generally higher than those of the stem part. Specifically， the IAA3 treatment exhibited the smallest TF value， which was not significantly different from the CK， while the largest value appeared in the SA2 treatment， and the values were 1.05 and 1.31 times of the CK， respectively. Accumulation of 88Sr in sunflower BCF values of 88Sr in various parts of sunflower were calculated according to the 88Sr contents in the root， stem， leaf and flower parts of sunflower and the 88Sr content in soil under plant hormone treatments， as shown in Fig. 4. It could be seen from Fig. 4 that the BCF values under various treatments were all larger than 1， and the three phytohormones all improved the BCF values of 88Sr， and the treatment effects of the three hormones overall ranked as SA > GA > IAA. The absorption capacity of the stem part to 88Sr was generally lower than other parts.
Discussion and Conclusions
The three phytohormones all improved the accumulation of 88Sr in sunflower plant， and increased the translocation and bioaccumulation factors of 88Sr， which were significantly higher than the CK. The optimal application concentrations of the three phytohormones （IAA， GA and SA） were 100， 500 and 100 mg/L， respectively. Under the 100 mg/LSA treatment， the adsorption capacity， TF and BCF of 88Sr in sunflower plant reached the highest values. This result accords with the research result obtained by Petr Soudek et al.[8]， who found that sunflower has a stronger 88Sr accumulation capacity. This might be because that phytohormones could improve the activity of atpase in cytomembrane and adjust the function of membrane proteins related to the translocation of metal elements， thereby helping metal elements to pass through cytomembrane and increasing its accumulation in cells[9]. Furthermore， Wang et al.[10] found that the external application of SA on Cassia tora could improve the absorption and accumulation of Al3+ in the root system of C. tora.
To sum up， rational application of plant hormone could reduce the adverse effects of pollutants to plant physiology， maintain normal growth and development of plant when alleviating stress， and facilitate the absorption， accumulation and translocation of pollution elements in plant.
References
[1] ZHANG QF. Phytoremediation of environment： Soil contamination and remediation[J]. Garden， 2010， 1（2）： 66-68.
[2] LI LH， ZHENG J， ZHANG C， et al. Effect investigation of strontium carbonate wastewater on ecological environment[J]. Chongqing Environmental Science， 2002， 24（2）： 63-64.
[3] ZHU YY， QIU TC. The behavior of fission products 90Sr， 137Cs and 144Ce in soil??plant system[J]. China Environmental Science， 1991， 11（4）： 266-269.
[4] MOHD I， SHIVENDRAVS. Promising role of plant hormones in translocation of lead in Sesbania drummondii shoots[J]. EnvironPollut， 2008， 15332（2）： 29-36. [5] ZHANG XX， WANG D， LI WF， et al. Studies on accumulation of 133Cs and 88Sr in Vicia faba Linn and irradiation damage effect[J]. Journal of Radiation Research and Radiation Processing， 2010， 28（1）： 48-52.
[6] WEN FP， WANG D， XU CH， et al. Uptake and distribution of 133Cs and 88Sr in sunflower[J]. Bulletin of Botanical Research， 2009， （5）： 592-596.
[7] ZHANG XX， WANG D， ZHONG MZ， et al. Response of Celosia cristata Linn to Cs and Sr stress and their accumulation characteristic[J]. Acta Agriculturae Nucleatae Sinica， 2010， 24（3）： 628-633.
[8] PETR S， SARKA V， ZUZANA V， et al. 137Cs and 90Sr uptake by sunflower cultivated underhydroponic conditions[J]. Journal of Environmental Radioactivity， 2006， 88： 236-250.
[9] PAZURKIEWICZK K， GALAS W， KITA A， et al. The effects of seleniumon the accumulation of some metals in Zea mays L. plants treated with indole??3??acetic acid[J]. Cellular??molecular Biology Letters， 2003， 8（1）： 97-103.
[10] WANG H， SHAN X， WEN B， et al. Effect of indole??3??acetic acid on lead accumulationin maize （Zea mays L.） seedlings and therelevant antioxidant response[J]. Environ. Exp. Bot， 2007， 61（1）： 246¨C253.