Abstract This study was conducted to elucidate the regulating mechanism of sodium nitroprussiate on seed germination and seedling growth of cherry tomato. After the treatment with different concentrations of sodium nitroprusside， the effects on the metabolites and key enzyme activities in carbonnitrogen metabolism of cherry tomato cultivar Zhuyun as an experimental material were investigated. The results showed that from seed germination to seedling period， the contents of starch and total nitrogen decreased， but the contents of soluble sugar， reducing sugar， sucrose and soluble protein increased firstly and then decreased； and free amino acids content increased gradually. Sodium nitroprusside made the contents of starch， sucrose and free amino acids higher than CK. From seed germination to seedling period in cherry tomato， the activities of amylase， glutamine synthetase （GS） and sucrose phosphate synthase （SPS） decreased； the activities of nitrate reductase （NR） and glutamate synthase （GOGAT） increased at first and decreased then； and the CK and the 0.25 mmol/L sodium nitroprusside treatments exhibited decreased sucrose synthase （SS） activity， and the trend was increasing at first and decreasing then after the treatment with 0.50 and 1.00 mmol /L sodium nitroprusside. Sodium nitroprusside treatment improved amylase activity； and the carbonnitrogen ratio of the CK increased at first and decreased then， while the values of other treatments tended to decrease. In addition， sodium nitroprusside did not affect seed germination potential and germination rate， but significantly improved biomass accumulation， root length and height of seedlings. These data suggest that sodium nitroprusside could affect the conversion of starch and sugar accumulation， delay the decomposition of total nitrogen and soluble protein， and achieve the effects of accelerating the accumulation of free amino acids， and promoting seed germination and seedling growth， and 0.50 mmol/L sodium nitroprusside has the best effect.
　　Key words Cherry tomatoes； Sodium nitroprusside； Seed germination； Seedling； Carbon and nitrogen metabolism； Key enzymes
　　Received： August 21， 2017 Accepted： November 9， 2017
　　Supported by National Natural Science Foundation of China （31660559）； Scientific Research Project of Kunming University （XJZZ1604）； Open Fund of Key Laboratory of Special Biological Resource Development and Utilization of Universities in Yunnan Province （ GXKJ201615）. 　　Yongfu ZHANG （1981-）， male， P. R. China， professor， PhD， devoted to research about resistance physiology of horticultural plants， Email： [email protected]
　　Cherry tomato （Lycopersicon esculentum var. cerasiforme Alef.） is a variety among the subspecies in Lycopersicon of Solanaceae family. It is an annual herb， which is native to South America. Due to its simple cultivation technique and strong adaptability， it is now cultivated in various provinces in China. The mature fruit of cherry tomato contain abundant saccharides， organic acids， mineral substances and vitamins， and is especially rich in vitamin C. The mature fruit has a proper sugaracid ratio， tastes good， and is small， resulting in a good market prospect[1]. NO is an important signal molecule in living body， which widely participated in the growth and development of plants and the regulation of response to various stresses[2-3]， such as the physiological processes including seed germination， leaf expansion， root growth， formation of lateral roots， programmed cell death and plant resistance reaction[4]. Carbon and nitrogen metabolism is the most basic physiological process of plant， and the metabolic intensity and the dynamic changes in plant growth and development process directly affect the formation and conversion of photosynthate， the absorption of mineral nutrition and the synthesis of protein[5]. Carbon and nitrogen metabolism greatly influences seed germination， seedling growth and yield and quality formation of cherry tobacco. Therefore， the research about the effects of NO on the carbon and nitrogen metabolic substances of cherry tomato and its related enzyme activities is of great significance to the promotion of the production， transportation and allocation of carbon and nitrogen substances and the promotion of normal seed germination and robust seedling growth.
　　Sodium nitroprusside as a NO donor has been widely applied to the improvement of seed germination rate and enhancement of stress resistance under stress. For instance， sodium nitroprusside could improve the germination rates of maize[6]， oat[7]， Perilla frutescens[8]， sorghum[9]， Allium mongolicum[10] and Silybum marianum[11] seeds under salt stress. The treatment with exogenous sodium nitroprusside could improve the soluble protein content in grape leaves under drought stress[12] and promote the accumulation of polysaccharides in Isatis tinctoria[13] and Dendrobium officinale[14]. Furthermore， The treatment with sodium nitroprusside could improve soluble protein content in cucumber seedlings， and increase plant height， stem diameter and root length[15]. It is speculated that sodium nitroprusside has a certain regulation effect on plant carbon and nitrogen metabolism， but there were no studies in this aspect. In view of this， Taiwan cherry tomato cultivar Zhuyun was selected an experimental material， which was treated with different concentrations of sodium nitroprusside， so as to investigate the effects of sodium nitroprusside on the carbonnitrogen metabolism and the activities of related enzymes in cherry tomato seeds from seed germination to seedling period. This study will provide a theoretical basis for the regulation of the nursery of cherry tomato seedlings with sodium nitroprusside. 　　Materials and Methods
　　Materials
　　The cherry tomato cultivar， Zhuyun was selected as an experimental material. The seeds were provided by Kunming vegetable seeds corporation. This cultivar is very early maturing， has the characteristics of strong growth vigor， high yield and proper soursweet taste， and is widely cultivated.
　　Experimental design
　　The experiment was carried out in May 2015. Three sodium nitroprusside concentration treatments were designed， and the concentrations were 0.25， 0.50 and 1.00 mmol/L， respectively. The concentrations of sodium nitroprusside were determined by trial tests， with distilled water as control check （CK）， and each treatment had four replicates. Large full seeds were selected and soaked in distilled water for 2 h. The seeds were then placed on the culture dishes laid with three layers of qualitative filter paper. Into each culture dish， 100 seeds were placed， and then 10 ml of different concentrations of sodium nitroprusside solutions were added， respectively. The seeds were placed in an illumination incubator under 26 ℃/16 ℃ （day temperature/nigh temperature） and 16 h/8 h （day time/night time） condition， and the photosynthetic photon flux density had a daily average value of 100 μmol/（m2·s）. After the seeds entered the germination period， strong germinated seeds were selected and sown in nutrition pots （8 cm×8 cm） filled with nursery substrate. Respectively， in the imbibition period， budding period， germination period， seedling formation period and seedling period， 20 seeds were selected randomly for the determination of the contents of carbon and nitrogen nutritive materials and the activities of related enzymes. Each treatments had three replicates.
　　Determination indexes and methods
　　The activity of amylase was determined by 3，5dinitrosaliclic acid. The activities of sucrose phosphate synthase （SPS） and sucrose synthetase （SS） were determined using the kit produced by Nanjing Jiancheng Bioengineering Institute， with the production of 1 μmol /（mg·min） sucrose as 1 enzymeactivity unit （U）. The activity of nitrate reductase （NR） was determined by sulfanilamide colorimetry[16]. The activities of glutamine synthetase （GS） and glutamate synthase （GOGAT） were determined the method of Wang et al.[17].
　　After sampling， seeds were ovendried at 105 ℃ and pulverized with 0.074 mm standard sieve. The dry powder， which passed through the sieve， was used for the determination of contents of starch， soluble sugar， reducing sugar， sucrose， total nitrogen， soluble protein and free amino acids. Starch content was determined according to the method of Xu et al.[18]. Soluble sugar content was determined by phenolsulfuric acid colorimetry； reducing sugar content was determined by 3，5binitro colorimetry； sucrose content was determined by resorcinol colorimetry； soluble protein content was determined by coomassie brilliant blue G250 development method； and free amino acid content was determined by acidic ninhydrin colorimetry[16]. Carbon contents in nonstructural sugar and starch could be calculated according to the proportions of carbon element in sugar and starch molecules. 　　After entering the germination period， germination indexes of seeds were determined as follows： Germination potential = Total number of germinated seeds within schedule time for reaching the peak period of germination/Number of tested seeds × 100%； and Germination rate = Total number of germinated seeds within schedule time/Number of tested seeds × 100%. In this experiment， the germination potential was calculated according to the total number of germinated seeds within 2 d， and the germination rate was calculated according to the total number of germinated seeds within 4 d. The total biomass of seedlings was measured directly with a balance （0.001 g）， and the root length and height and young seedlings were measured with a ruler. All the determination was repeated for three times， and the values were averaged.
　　Data processing
　　Data were subjected to the analysis of significance of difference by Duncans method using SPSS 22.0 （P<0.05）， and plotting was performed with Excel 2010.
　　Results and Analysis
　　Effect of sodium nitroprusside on carbon metabolism from seed germination to seedling period
　　Starch and sugar contents
　　Saccharides and starch contents in plant are important indexes for carbon conversion and accumulation. It could be seen from Fig. 1 that from seed germination to seedling period of cherry tomato， the starch content decreased gradually， while the contents of soluble sugar， reducing sugar and sucrose exhibited a trend of increasing at first and decreasing then. In the imbibition period， treatments T1， T2 and T3 had starch contents 23.72%， 37.25% and 27.16% higher than the CK， respectively； from the imbibition period to the budding period， the starch contents decreased sharply， and then decreased slowly； and from the imbibition period to the seedling period， the starch contents in the T1， T2， T3 and CK decreased by 92.57%， 93.89%， 92.91% and 90.26%， respectively. In the imbibition period， the solution sugar contents in treatments T1 and T2 and the CK were 107.40%， 67.09% and 57.73% higher than that of treatment T3， respectively； in the budding period， the soluble sugar contents in treatments T1， T2 and T3 and the CK increased by 13.97%， 27.41%， 42.99% and 22.47%， respectively， compared with those in the imbibition period； but from the budding period to the seedling period， the soluble sugar contents in treatments T1， T2 and T3 and the CK decreased by 86.46%， 81.33%， 78.26% and 80.04%， respectively. As to the content of reducing sugar， it increased sharply from the imbibition period to the budding period， and the reducing sugar contents in treatments T1， T2 and T3 and the CK increased by 190.69%， 332.42%， 182.30% and 116.83%， respectively； from the budding period to the seedling period， the reducing sugar content exhibited a sharp decreasing trend， and the values of the various treatments decreased by 83.59%， 81.92%， 81.94% and 80.56%， respectively. The sugar content exhibited an increasing trend from the imbibition period to the budding period， during which the sugar contents of treatments T1， T2 and T3 and the CK increased by 124.68%， 144.24%， 164.13% and 81.73%， respectively， while from the budding period to the seedling period， the sugar contents of the various treatments were on the decrease， and decreased by 68.47%， 74.08%， 75.24% and 75.87%， respectively， indicating that a proper concentration of sodium nitroprusside could promote the conversion and accumulation of starch， and the 0.50 mmol /L sodium nitroprusside treatment has the best effect in promoting carbon metabolism. 　　1. Imbibition period； 2. Budding period 3. Germination period； 4. Seedling formation period； 5. Seeding period. Similarly hereinafter.
　　Fig. 1 Effects of sodium nitroprusside on starch and sugar contents in cherry tomato seeds from seed germination to seedling period
　　Agricultural Biotechnology2018
　　Activities of key enzymes for carbon metabolism
　　Amylase controls the hydrolysis from seed germination to seedling period. SPS is the key enzyme controlling sucrose synthesis， which adjusts the distribution of photosynthate between starch and sucrose. SS exists in cytoplasm， and it decomposes sucrose to produce adenosine diphospate glucose and fructose， for the synthesis of carbohydrates such as starch. Fig. 2 showed that from the imbibition period to the budding period， the activity of amylase in various treatments had no big change， and showed an order of T2>T1>T3>CK， while from the budding period to the seedling period， the activity of amylase was on a sharp decrease trend， and the amylase activity of treatments T1， T2 and T3 and the CK decreased by 84.67%， 77.74%， 84.49% and 85.34%， respectively， and in the seedling period， treatments T1 and T3 and the CK exhibited amylase activity lower than that of treatment T2 by 34.33%， 43.28% and 53.73%， respectively. The SPS activity was on the decrease. In the imbibition period， the values of treatments T1， T2 and T3 were lower than that of the CK by 25.21%， 8.52% and 2.53%， respectively； from the imbibition period to the seedling period， the SPS activity of the treatments T1， T2 and T3 and the CK decreased by 89.87%， 94.20%， 95.18% and 91.04%， respectively； and at the seeding period， the SPS activity of treatments T1， T2 and T3 was lower than that of the CK by 15.45%， 40.79% and 47.56%， respectively. As to the SS activity， the SS activity of treatments T2 and T3 increased by 24.43% and 34.84%， respectively from the imbibition period to the budding period； from the budding period to the seedling period， the SS activity decreased greatly， and the values of treatments T1， T2 and T3 and the CK decreased by 90.87%， 94.55%， 97.22% and 87.46%， respectively. It was indicated that sodium nitroprusside greatly affected the activities of amylase， SPS and SS from germination to seedling period of cherry tomato seeds.
　　Effect of sodium nitroprusside on nitrogen metabolism from seed germination to seedling period
　　Total nitrogen， soluble protein and amino acid contents
　　Protein is the endproduct of nitrogen metabolism. Amino acids are the main raw materials for the synthesis of protein， as well as the main products of protein degradation. It could be seen from Fig. 3 that the total nitrogen content of various treatments was on the decrease， the total nitrogen contents of treatments T1， T2 and T3 were lower than that of the CK by 30.53%， 27.67% and 1.41% in the budding period， respectively； and from the imbibition period to the seedling period， the total nitrogen contents of treatments T1， T2 and T3 and the CK decreased by 67.86%， 61.50%， 67.69% and 84.17%， respectively. The soluble protein contents of the various treatments were on the increase from the imbibition period to the budding period； in the budding period， the soluble protein contents of treatments T1， T2 and T3 were higher than that of the CK by 17.76%， 32.01% and 13.08%， respectively； and from the budding period to the seedling period， the soluble protein contents of treatments T1， T2 and T3 and the CK decreased by 80.75%， 82.83%， 81.61% and 76.40%， respectively. The free amino acid contents of treatments T1， T2 and T3 and the CK were on the increase overall， and CK had the lowest value in various periods. From the imbibition period to the seedling period， the free amino acid contents of treatments T1， T2 and T3 and the CK increased by 60.07%， 67.38%， 57.46% and 60.72%， respectively； and in the seedling period， the free amino acid contents of treatments T1， T2 and T3 were higher than that of the CK by 22.05%， 32.84% and 46.19%， respectively. It was indicated that sodium nitroprusside could retard the degradation of nitrogen for the seed germination to seedling period of cherry tomato， and promote the accumulation of soluble protein before the budding period and the conversion during after the budding period， thereby improving free amino acid content. 　　Fig. 2 Effects of sodium nitroprusside on activities of key enzymes for carbon metabolism from seed germination to seedling period
　　Fig. 3 Effects of sodium nitroprusside on total nitrogen， soluble protein and amino acid contents in cherry tomato seeds from seed germination to seedling period
　　Activities of key enzymes for nitrogen metabolism
　　NR is a key regulatory enzyme and ratelimiting enzyme during plant nitrogen assimilation. GS is a key enzyme catalyzing ammonia assimilation. GOGAT is also a key enzyme for the nitrogen assimilation in plant. It could be seen from Fig. 4 that after the treatment with sodium nitroprusside， the activities of NR and GOGAT both showed a trend of increasing at first and decreasing then. The peak value of NR activity appeared in the budding period， during which the NR activity of treatments T1， T2 and T3 was lower than that of the CK by 16.68%， 15.99% and 6.60%， respectively； from the budding period to the seedling period， the NR activity of treatments T1， T2 and T3 and the CK decreased by 43.25%， 71.26%， 52.09% and 80.69%， respectively； and in the seedling period， the NR activity of treatments T1， T2 and T3 were higher than that of the CK by 294.93%， 62.54% and 204.36%， respectively. From the imbibition period to the seedling period， the GS activity was on the decrease overall. In the imbibition period， the GS activity of treatments T1， T2 and T3 was lower than that of the CK by 15.75%， 48.47% and 34.56%， respectively； and in the seedling period， the GS activity of treatments T1， T2 and T3 and the CK decreased by 72.23%， 84.87%， 84.11% and 83.79%， respectively， compared with the imbibition period. As to the peak value of GOGAT activity， except that the CK exhibited a peak value in the germination period， other treatments reached their peak values in the budding period， during which the GOGAT activity of treatment T1， T2， and T3 was higher than that of the CK by 8.88%， 27.74% and 16.77%， respectively， and to the seedling period， the GOGAT activity of treatments T1， T2 and T3 and the CK was lower than their respective peak value by 61.78%， 58.34%， 64.39% and 69.54%， respectively. It was indicated that the sodium nitroprusside treatment had a certain effect of improving the nitrogen metabolism of cherry tomato seeds from germination to seedling period.
　　Effects of sodium nitroprusside on carbon content and carbonnitrogen ratio from seed germination to seedling period
　　Carbon and nitrogen contents are important nutrient indexes of plants， while carbonnitrogen ratio reflects the deviation of main nutrient substance in plants. Fig. 5 showed that sodium nitroprusside could retard the carbon loss in cherry tomato seeds from germination to seedling period. In the imbibition period， the carbon contents of treatments T1， T2 and T3 were higher than that of the CK by 31.21%， 45.58% and 18.23%， respectively； and in the seedling period， the carbon contents of treatments T1， T2 and T3 and the CK decreased by 90.50%， 89.57%， 84.93% and 85.38%， respectively， compared with the imbibition period. The carbonnitrogen ratio of the CK exhibited a peak value in the seedling formation period which was higher than the value in the imbibition period by 134.19%， and then decreased rapidly. From the imbibition period to the seedling period， the carbonnitrogen ratio of treatments T1， T2 and T3 decreased by 70.45%， 72.90% and 53.35%， respectively. Apparently， sodium nitroprusside greatly affected the carbon content and carbonnitrogen ratio of cherry tomato seeds from seed germination to the seedling period. 　　Fig. 4 Effects of sodium nitroprusside on activities of key enzymes for nitrogen metabolism from seed germination to seedling period
　　Fig. 5 Effects of sodium nitroprusside on carbon content and carbonnitrogen ratio from germination to seedling period
　　Effects of sodium nitroprusside on germination and seedling growth indexes of cherry tomato seeds
　　It could be seen from Table 1 that sodium nitroprusside treatments could improve the seed germination rate and germination potential of cherry tomato to certain degrees， but the differences were not significant. After the treatment， the seedling biomass， root length and seedling height were all significantly higher than the CK. Treatments T1， T2 and T3 exhibited the biomass higher than the CK by 33.33%， 100.00% and 108.33%， respectively， the root lengths longer than the CK by 26.49%， 59.90%， 56.44%， respectively， and the seedling heights higher than the CK by 17.35%， 35.54% and 43.39%， respectively. Obviously， the treatment with sodium nitroprusside could promote the growth of seedlings of cherry tomato.
　　Table 1 Effects of sodium nitroprusside on germination and seedling growth indexes of cherry tomato seeds
　　TreatmentGermination potential∥%Germination rate∥%Biomass∥g/plantRoot length∥cmSeedling height∥cm
　　T198.67±4.12 a99.67±2.05 a0.16±0.02 b5.11±0.32 b2.84±0.11 b
　　T299.33±6.33 a100.00±0.00 a0.24±0.03 a6.46±0.28 a3.28±0.26 a
　　T398.50±3.09 a98.33±4.06 a0.25±0.01 a6.32±0.57 a3.47±0.19 a
　　CK97.45±8.02 a98.25±5.33 a0.12±0.02 c4.04±0.29 c2.42±0.23 c
　　Conclusions and Discussion
　　The carbon metabolism of plant include three stages， i.e.， the assimilation of carbon， the transportation and conversion of carbohydrates and the accumulation of carbon. The assimilation of carbon refers to the conversion of inorganic carbon into organic carbon through photosynthesis in chloroplast. The transportation and conversion of carbohydrates refers to the transportation of phosphotriose to cytoplasm through chloroplast for the synthesis of sucrose and the further conversion to monosaccharide. The accumulation of carbon is mainly performed in the mode of sucrose and starch. The change of carbon metabolism directly affects the formation and conversion of carbohydrates and the synthesis and decomposition of protein[19-20]. Researches show that the treatments with sodium nitroprusside[21]， saccharides[22] and amino acids[23] all could remarkably affect the carbon and nitrogen metabolism of crops. The results of this study showed that in cherry tomato seeds， from seed germination to seedling period， the starch content decreased gradually， and the contents of soluble sugar， reducing sugar and sucrose showed a trend of increasing at first and decreasing then， indicating that the treatment with sodium nitroprusside greatly affected their variation amplitudes. It was also found that in the seeds treated with sodium nitroprusside， from seed germination to seedling period， the activity of amylase changed slowly before the budding period and then decreased sharply， which is because that a higher amylase activity is beneficial to the decomposition of starch， but after a period of time， the starch content decreases to a lower level， and the activity of amylase also decreases with it. The treatment with sodium nitroprusside retarded the descend range of amylase activity and accelerated the decomposition of starch. SPS and SS are the key enzymes promoting sucrose to enter various metabolic pathways. Generally， SS plays a role of decomposing sucrose[24]. SPS could catalyze the synthesis of sucrose， and its activity is negatively correlated with starch accumulation， and positively correlated with the formation of sucrose. From seed germination to seedling period， the activities of SPS and SS exhibited a gradually decreasing trend overall， indicating that during the seed germination period， the starch decomposition and sucrose formation were both slowed down， and the rate of carbon metabolism decreased. However， compared with the CK， the 0.50 mmol/L sodium nitroprusside treatment effectively retarded the reduction of the activities of the two kinds of enzymes， and inhibited the reduction of carbon metabolism to a certain degree. Nitrogen metabolism includes the reduction and assimilation of nitric nitrogen and the conversion and synthesis of organic nitrogen compounds. The inorganic nitrogen absorbed into plant mostly enters amino acids， and further participates in the synthesis of protein， and a small part participates the metabolism of nitrogencontaining substances including nucleic acid. The main pathway of nitrogen assimilation of plant is to reduce nitrate into ammonium which directly participates the synthesis and conversion of amino acids， during which key enzymes including NR， GS and GOGAT participated in the catalysis and regulation. The synthesis of protein is performed in cells with amino acids as the main substrate， followed by the modification， classification， transportation and storage of protein， and the products become the constituent part of plant organism. Meanwhile， the synthesis of protein is coordinated with the carbon metabolism of plant. There are studies reporting that the treatment of plant with sodium nitroprusside could reduce the content of soluble protein[12，15]. In this study， from seed germination to the seedling period， the total nitrogen content in cherry tomato seeds gradually decreased， the GS activity was also on the decease overall， the free amino acid content increased gradually， and the soluble protein content and GOGAT and NR activities increased at first and decreased then. It was indicated that in the process， nitrogen would be converted into protein on one hand， and would be lost on the other hand； the increase of the amino acid content was caused by the decomposition of protein， and the decrease of soluble protein content in the germination period was due to that the protein stored in seeds was gradually converted to amino acids which were supplied for the demand from seed germination and seedling growth， while no protein was synthesized in seedlings； and the treatment with sodium nitroprusside alleviated the decrease of total nitrogen， accelerated the increase of amino acid content， and promoted the increase of soluble protein content before the budding period. It is thus could be seen that the treatment with sodium nitroprusside could promote the assimilation and conversion metabolism of nitrogen from seed germination to seedling period. 　　Carbonnitrogen metabolism is the most basic metabolic process of crops， and greatly affects the growth and development， yield and quality of crops. Nitrogen metabolism depends on the carbon source and energy provided by carbon metabolism， while carbon metabolism needs the enzymes and photosynthetic pigments provided by carbon metabolism. The coordination of carbon and nitrogen is crucial to the growth and development and yield of crops[25]. The results of this study showed that from the seed germination to seedling period of cherry tomato， the total carbon content gradually decreased， and except that the CK exhibited a carbonnitrogen ratio trend of increasing at first and decreasing then， sodium nitroprusside treatments showed steadily decreasing carbonnitrogen ratio. Furthermore， sodium nitroprusside treatments promoted seed germination and seedling growth of cherry tomato， which accords with the research result of Zheng et al[21]. To sum up， the treatment with sodium nitroprusside could promote the conversion of carbon and nitrogen nutrition from seed germination to seedling period of cherry tomato， and accelerate material accumulation and promote seed germination and seedling growth， and the 0.50 mmol/L treatment has the best effect.
　　References
　　[1] LIU SJ， WANG RL， JIANG HF， et al. The effect of freshkeeping on fruit and vegetable using edible film[J]. Journal of Zhengzhou Grain College， 2004， 25（4）： 58-61.
　　[2] CRAWFORD NW， GUO FQ. New insights into nitric oxide metabolism and regulatory functions[J]. Trends in Plant Science， 2005， 10（4）： 195-200.
　　[3] BESSONBARD A， PUGIN A， WENDEHENNE D. New insights into nitric oxide signaling in plant[J]. Annual Review of Plant Biology， 2008， 59： 21-39.
　　[4] ZHANG YK， HAN XJ， JIN H， et al. Effects of exogenous nitric oxide on photosynthetic， bioluminescent characteristics and mineral element contents in tomato under copper stress [J]. Journal of Plant Nutrition and Fertilizer， 2010， 73（1）： 172-178.
　　[5] TANG XM， ZHONG RC， JIE HK， et al. Effect of interplanting peanut on metabolites and key enzyme activities of carbonnitrogen metabolism of cassava[J]. Chinese Agricultural Science Bulletin， 2011， 27（3）： 94-98.
　　[6] WANG F， WANG HN. Protective Effects of exogenous nitric oxide on oxidative damage of maize seedling leaves under NaCl stress[J]. Acta Agrectir Sinica， 2012， 20 （6）：1117-1122.
　　[7] SU T， LONG RJ， WEI XH， et al. Protective effects of exogenous nitric oxide on oxidative damage in oat seedling leaves under NaCl stress [J]. Acta Prataculturae Sinica， 2008， 17（5）： 48-53. 　　[8] ZHANG CP， HE P， DU DD， et al. Effect of exogenous nitric oxide donor SNP on seed germination and antioxidase activities of Perilla frutescens seedlings under NaCl stress[J]. Journal of Chinese Medicinal Materials， 2011， 34（5）： 665-669.
　　[9] SHI R， YANG LL， LIU SN， et al. Regulation of external NO on physiological responses of sorghum seedlings under NaCl stress[J]. J Jiangsu Agric Sci， 2016， 44（8） ： 139-142.
　　[10] LU Y， WANG P， SONG ZW. Effect of seed soaking with exogenous NO on seed germination and physiological characteristics of Allium mongolicum Regel. under NaCl stress[J]. Acta Agriculturae BorealiSinica， 2011， 26（2）： 207-212.
　　[11] ZHANG XQ， WANG KC， ZHANG YN， et al. Effects of exogenous nitric oxide on physiology of seed germination and seedling growth of Silybum marianum under NaCl stress[J]. Chinese Traditional and Herbal Drugs， 2013， 44（22）： 3216-3222.
　　[12] ZHANG YF， HE TF， NIU YF， et al. Effects of sodium nitroprusside on droughtresistance physiology in grape under drought stress[J]. Guangdong Agricultural Sciences， 2014， 41（24）： 40-44.
　　[13] MAO YB， WEI XH. Effects of exogenous nitric oxide on lipid peroxidation antioxidase fluorescence of Isatis indigotica leaves under drought stress[J]. Pratacultural Science， 2010， 27（6）： 97-101.
　　[14] JIANG TY， ZHUO Y， TANG M， et al. Effects of exogenous nitric oxide on growth and polysaccharide accumulation of protocorm of Dendrobium officinale[J]. Jiangsu Agricultural Sciences， 2016， 44（4）： 257-260.
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