Effects of Exogenous Vc on Seed Germination and Physiological Properties of Oil Sunflower（Helianthus annuus）under Salt Stress

Jinglin LU，Yanjuan GAO，Yujiao CHANGCollege of Agriculture and Biotechnology，Hexi University，Zhangye 734000，China

Effects of Exogenous Vc on Seed Germination and Physiological Properties of Oil Sunflower（Helianthus annuus）under Salt Stress

Jinglin LU*，Yanjuan GAO，Yujiao CHANG
College of Agriculture and Biotechnology，Hexi University，Zhangye 734000，China

［Objective］This study aimed to provide the theoretical and technical basis for alleviating salt damages in production practice of oil sunflower （Helianthus annuus）.［Method］Seeds of oil sunflower were used as experimental materials and treated with 120 mmol/L NaCl solution and 0-200 mg/L Vc solution during the germination process，to investigate the effects of exogenous Vc on seed germination and physiological properties of oil sunflower under salt stress. ［Result］Under salt stress，with the increase of Vc concentration，germination potential and germination rate of oil sunflower seeds，superoxide dismutase （SOD）and peroxidase （POD）activities and proline （Pro）content of oil sunflower seedlings increased first and then declined，which reached the maixmum in 80 mg/L Vc treatment，120 mg/L Vc treatment and 80 mg/L Vc treatment，respectively；malondialdehyde（MDA）content of oil sunflower seedlings declined first and then increased，which reached the minimum in 160 mg/L Vc treatment.［Conclusion］To varying degrees，Vc could improve germination potential and germination rate of oil sunflower seeds and promote seedling growth under salt stress，thus alleviating the damages of salt stress to seed germination and seedling growth of oil sunflower.

Oil sunflower（Helianthus annuus）；Vitamin C；Salt stress；Seed germination；Physiological indicators

Materials and Methods

Materials

Seeds of oil sunflower cultivar Hysun139 were used as expwerimental materials，which were provided by Zhangye Denong Seed Industry Co.，Ltd.

Experimental design

According to Yu et al.［11］，under NaCl stress，the appropriate salt concentration for identification of salt tolerance in oil sunflower in germination period is 120 mmol/L.In this study，seeds of oil sunflower were treated with the same concentration of NaCl and different concentrations of Vc solution（Table 1）.

Table 1 Different treatment combinations of oil sunflower seeds and seedlings

Pretreatment and germination of seeds

Plump seeds with consistent size were selected，disinfected with 0.1% HgCl2for 10 min，rinsed three times with distilled water，and soaked with distilled water for 8 h.Surface moisture was absorbed；50 seeds were placed on two layers of filter paper in a petri dish，and added with the prepared experimental solution along the wall of petri dish to keep the filter paper moist. All the seeds were incubated in an incubator at 25℃.The original experimental solution was supplemented every day to keep the filter paper moist.Each treatment was repeated four times.The germination test lasted seven days；germination indicators of oil sunflower seeds and growth and physiological indicators of oil sunflower seedlings were determined and calculated.

Determination of related indicators Determination of germination potential and germination rate Seed germination potential（A）=G1/Gn× 100%；seed germination rate （G）= Ga/Gn×100%.Where，G1 indicated the number of seeds germinated at 4 d；Gn indicated the number of experimental seeds；Ga indicated the number of seeds germinated at 7 d.

Determination of physiological indicators Relative conductivity was measured using DDS-307 conductivity meter；superoxide dismutase（SOD）activity was determined with nitroblue terazolium（NBT）recovery assay；peroxidase （POD）activity was determined with guaiacol colorimetric method； malondialdehyde （MDA）content was determined with thiobarbituricacid （TBA）colorimetric method；proline （Pro）content was determined with acidic-ninhydrin colorimetric method［12］.Determination of each indicator was repeated three times.

Data processing

Experimental data were analyzed using Excel 2003 software.DPS6.55 software was employed for variance analysis and multiple comparisons. The significance test of difference was performed with Duncan method.

Results and Analysis

Effects of Vc on seed germination of oil sunflower under NaCl stress

As shown in Fig.1 and Fig.2，after addition of different concentrations of Vc solution under NaCl stress，germination potential and germination rate of oil sunflower seeds increased first and then declined with the increase of exogenous Vc concentration.To be specific，80 mg/L Vc treatment led to the best result，in which germination potential and germination rate of oil sunflower seeds were improved by 15.6%and 14.8%compared with CK respectively，indicating that an appropriate amount of Vc could to some extent alleviate the inhibitory effect of salt stress and promote seed germination.

Effects of Vc on SOD and POD activities of oil sunflower seedlings under NaCl stress

As important protective enzymes of plant cell membranes，SOD and POD are generally used as physiological indicators to evaluate stress tolerance in plants.As shown in Fig.3 and Fig.4，under NaCl stress，with the increase of exogenous Vc concentration，SOD and POD activities of oil sunflower seedlings increased first and then declined，which varied significantly compared with the control；specifically，SOD activity of oil sunflower seedlings in treatments with addition of different concentrations of Vc was improved by 19.3%-28.4%andPOD activity was improved by 17.5%-29.8% compared with the control，which both reached the maximum in 120 mg/L Vc treatment.Therefore，salt stress could reduce oxidase activities，but an appropriate concentration of Vc could improve SOD and POD activities of oil sunflower seedlings and maintain the integrity of cell membranes.

Effects of Vc on MDA content of oil sunflower seedlings under NaCl stress

MDA is a final product of membrane lipid peroxidation and an important symbol reflecting the degree of membrane system injury.As shown in Fig.5，under NaCl stress，MDA content of oil sunflower seedlings in 40-200 mg/L Vc treatments was significantly lower compared with control.To be specific，MDA content of oil sunflower seedlings reached the minimum in 160 mg/L Vc treatment，which indicated that a certain concentration of Vc could decline the level of membrane lipid peroxidation and reduce adverse effects of salt stress on oil sunflower seedlings.

Effects of Vc on proline content of oil sunflower seedlings under NaCl stress

Proline is important and effective organic osmoregulatory substance in plant cells.As shown in Fig.6，under NaCl stress，proline content of oil sunflower seedlings increased first and then declined with the increase of Vc concentration；to be specific，proline content of oil sunflower seedlings in 40.0-120.0 mg/L treatments varied significantly compared with the control；proline content of oil sunflower seedlings reached the maximum in 80 mg/L treatment，which was improved by 31.2%compared with the control，indicating that certain concentrations of Vc could improve osmotic adjustment ability of cells in oil sunflower seedlings under salt stress.

Conclusion and Discussion

As an important stage of plant ontogeny，seed germination directly affects plant growth and yield formation. So far，a large number of studies have confirmed that salt stress can inhibit normal germination of seeds［13-17］.Under high salt conditions，the integrity of cell membranes is damaged，which leads to reduction or even loss of cell membrane permeability，high-level accumulation of a large amount of Na+and Cl-，deficiency of K+and Ca2+，and intracellular ion imbalance，thus triggering a series of metabolic disorders. Wang et al.［18］confirmed that 70 mmol/L Nacl solution exhibited the most significant promoting effect on germination rate，relative salt damage rate，total dry weight per hundred plant，average hypocotyl length and other indicators of oil sunflower seeds. According to the results，after addition of different concentrations of Vc，germination potential and germination rate of oil sunflower seeds in 120 mmol/L NaCl treatment increased first and then reduced with the increase of exogenous Vc concentration；80 mg/L Vc treatment led to the best result，in which germination potential and germination rate of oil sunflower seeds were improved significantly.

As important protective enzymes in plants，SOD and POD are very sensitive to adversity［19］.To be specific，SOD can catalyze disproportionation reactions of superoxide ion free radicals to eliminate toxic ions；POD can remove peroxides，thus playing an important role in plant resistance.MDA is a product of lipid peroxidation and its content is an important indicator of intracellular reactive oxygen content and membrane damage.Proline is an osmoregulatory substance in plants，which can accumulate significantly under environmental stress，thus contributing to improving water-holding capacity of cells and protecting protoplasm.In this study，with the increase of Vc concentration，SOD and POD activities and proline content of oil sunflower seedlings increased first and then declined.Specifically，SOD and POD activities reached the maximum in 120 mg/L Vc treatment；proline content reached the maximum in 80 mg/L Vc treatment.MDA content of oil sunflower seedlings declined first and then increased，which reached the minimum in 160 mg/L Vc treatment.The results indicate that adding an appropriate amount of exogenous Vc under salt stress can alleviate the damages of salt stress to seedlings.

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外源Vc對鹽脅迫下油葵種子萌發(fā)和幼苗生理特性的影響

盧精林*，高彥娟，常玉嬌 （河西學院農(nóng)業(yè)與生物技術(shù)學院，張掖 734000）

［目的］為實際生產(chǎn)中緩解油葵鹽害提供理論和技術(shù)依據(jù)。［方法］以油葵種子為試驗材料，在種子萌發(fā)過程中選用120mmol/L NaCl鹽脅迫和0～200 mg/L Vc溶液進行處理，研究外源Vc對鹽脅迫下油葵種子萌發(fā)指標和幼苗生理特性的影響。［結(jié)果］在鹽脅迫下，隨著Vc溶液濃度的增加，油葵種子發(fā)芽勢和發(fā)芽率、幼苗超氧化物岐化酶（SOD）和過氧化物酶（POD）活性、脯氨酸（Pro）含量均呈現(xiàn)先升高后降低的趨勢，分別以80 mg/L、120 mg/L、80 mg/L的Vc處理達到最大值；幼苗丙二醛（MDA）含量呈現(xiàn)先降后升的趨勢，以160 mg/L Vc處理達到最小值。［結(jié)論］Vc能不同程度地提高鹽脅迫條件下油葵種子的發(fā)芽率、發(fā)芽勢，促進幼苗生長，緩解鹽脅迫對油葵種子萌發(fā)和幼苗生長的危害。

油葵；維生素C；鹽脅迫；種子萌發(fā)；生理指標

O il sunflower（Helianthus annuus）is an important oil crop with strong adaptability and high tolerance to barren and saline-alkali，which can grow and propagate normally in saline-alkaline land containing a certain amount of salt［1］.At present，improving salt tolerance in plants has attracted much attention；adding exogenous substances to regulate antioxidant components in plants has become an effective means for alleviating the damages caused by abiotic stress in plants［2］.As coenzymes involved in some important enzymatic reactions or components of the coenzymes，vitamins play an important role in growth and physiological function regulation of plants，which can enhance seed vigor，stimulate plant growth and development，increase yield，and improve quality and resistance［3］.Studies have shown that adding exogenous Vc can improve salt tolerance in wheat［3］，maize［4］，rice［5］，cucumber［6-7］，melon［8］，cabbage［9］，alfalfa［10］and other plants.However，little information is available on the effects of exogenous VC on seed germination and physiological and biochemical properties of oil sunflower.In order to investigate the physiological mechanism of the effects of Vc on salt tolerance in oil sunflower，in this study，oil sunflower seeds were used as experimental materials and treated with different concentrations of Vc solution under NaCl stress to analyze the effects of different concentrations of exogenous Vc on seed germination and physiological properties of oil sunflower，which laid the theoretical and technical foundation for alleviating salt damages in production practice of oil sunflower.

盧精林（1963-），男，甘肅民勤人，副教授，碩士，從事種子生產(chǎn)研究，E-mail：Lujl863@163.com。*通訊作者。

2014-12-25

2015-02-16

.E-mail:Lujl863@163.com

December 25，2014Accepted:February 16，2015