南京农业大学学报  2018, Vol. 41 Issue (3): 422-428   PDF    
http://dx.doi.org/10.7685/jnau.201706044
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文章信息

董慧杰, 韩克, 侯喜林, 张志硕, 胡春梅
DONG Huijie, HAN Ke, HOU Xilin, ZHANG Zhishuo, HU Chunmei
6种不结球白菜材料叶片抗氧化活性的比较及花青苷合成相关基因的表达分析
Comparison of anthocyanins antioxidant activities and the expression analysis of genes related to anthocyanins biosynthesis in the leaves of six non-heading Chinese cabbage materials
南京农业大学学报, 2018, 41(3): 422-428
Journal of Nanjing Agricultural University, 2018, 41(3): 422-428.
http://dx.doi.org/10.7685/jnau.201706044

文章历史

收稿日期: 2017-06-29
6种不结球白菜材料叶片抗氧化活性的比较及花青苷合成相关基因的表达分析
董慧杰 , 韩克 , 侯喜林 , 张志硕 , 胡春梅     
南京农业大学园艺学院/作物遗传与种质创新国家重点实验室, 江苏 南京 210095
摘要[目的]本文旨在比较不结球白菜不同材料间叶片总花青苷含量及其抗氧化活性,探究花青苷合成相关基因的表达特性。[方法]以6种不结球白菜材料为试材,采用DPPH(1,1-二苯基-2-三硝基苯肼)法和铁离子还原能力(FRAP)法检测了叶片提取液抗氧化活性,并测定了花青苷合成相关结构基因(BrcF3H、BrcDFR、BrcANS、BrcCHI、BrcCHS、BrcUFGT)和调节基因(BrcTT8、BrcTTG1、BrcMYB75、BrcMYB90、BrcGL3、BrcEGL3.1、BrcEGL3.2)的表达水平。[结果]在6种不结球白菜材料中,深紫色材料NJZX1-4的总花青苷含量最高,为(801.5±57.4)μg·g-1。6种材料叶片提取液的DPPH自由基清除率为(49.31±3.91)%~(84.94±6.20)%,铁离子还原能力为(256.8±136.3)~(1 279.5±202.0)μg·g-1,其中紫色材料NJZX1-1叶片的DPPH自由基清除率和铁离子还原能力最强,且总花青苷含量与DPPH自由基清除率和铁离子还原能力均存在极显著正相关。结构基因BrcF3H、BrcDFR、BrcANS和调节基因BrcTT8在6种材料中的表达量与总花青苷的含量呈正相关。调节基因BrcMYB75BrcTTG1在紫色材料NJZX1-4叶片中具有较高的表达量,而BrcEGL3.2BrcMYB90基因在所有材料中均无表达。[结论]不结球白菜不同材料间花青苷含量和抗氧化活性存在显著差异,且紫色材料富含的花青苷在高抗氧化性方面发挥了重要作用。此外,3个结构基因和3个调节基因的表达水平与总花青苷含量密切相关,在调控不结球白菜叶片着色过程中起重要作用。
关键词不结球白菜   花青苷   抗氧化活性   结构基因   调节基因   
Comparison of anthocyanins antioxidant activities and the expression analysis of genes related to anthocyanins biosynthesis in the leaves of six non-heading Chinese cabbage materials
DONG Huijie, HAN Ke, HOU Xilin, ZHANG Zhishuo, HU Chunmei    
College of Horticulture/State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing 210095, China
Abstract: [Objectives] The aim of this study was to compare the antioxidant activity of total anthocyanins content in the leaves of different non-heading Chinese cabbage materials, and to investigate the expression patterns of genes related to anthocyanins biosynthesis in these materials. [Methods] We used six materials of non-heading Chinese cabbages, and measured the antioxidant activities of leaves by using DPPH(1, 1-diphenyl-2-picrylhydrazyl)and FRAP(ferric reducing ability of plasma) methods. In addition, we determined the expression levels of related structural genes(BrcF3H, BrcDFR, BrcANS, BrcCHI, BrcCHS, BrcUFGT)and regulatory genes(BrcTT8, BrcTTG1, BrcMYB75, BrcMYB90, BrcGL3, BrcEGL3.1, BrcEGL3.2)related to anthocyanins biosynthesis. [Results] Among six materials, total anthocyanins content was the highest in the deep purple material NJZX1-4, which was(801.5±57.4)μg·g-1. DPPH free radical scavenging rates of six materials were(49.31±3.91)%-(84.94±6.20)%, and FRAP values were(256.8±136.3)-(1 279.5±202.0)μg·g-1, which was higher in purple material NJZX1-1 than those of other materials. The correlation among total anthocyanins content, DPPH radical scavenging rate and FRAP antioxidant capacity were extremely significant. Moreover, we found that the expression of anthocyanins structural genes(BrcF3H, BrcDFR and BrcANS)and regulatory genes(BrcTT8)were positively correlated with the content of total anthocyanins. Regulatory genes BrcEGL3.2 and BrcMYB90 had no expression in all materials, and BrcMYB75 and BrcTTG1 were highly expressed in the deep purple leaf material NJZX1-4. [Conclusions] There were significant differences in total anthocyanins content and antioxidant activity among different non-heading Chinese cabbage materials, and anthocyanins played an important role in antioxidant activities in leaves. The expression levels of three anthocyanins structural genes and three regulatory genes had close relation with the accumulation of anthocyanins in leaves, indicating that these genes might play an important role in regulating the coloring process in leaves of non-heading Chinese cabbage.
Key words: non-heading Chinese cabbage    anthocyanins    antioxidant activity    structural genes    regulatory genes   

不结球白菜(Brassica rapa ssp. chinensis)因其适应性广、营养丰富、栽培方便和生长周期短, 而受到人们的青睐。紫色不结球白菜叶片上、下表皮具有较大的颜色差异, 通常上表皮呈深紫色或亮紫色, 下表皮紫色分布不均匀, 富含花青苷[1-2]。花青苷主要存在于植物液泡中, 使植物花、叶片、果实、种子等呈现不同色彩[3]。研究表明, 花青苷是最理想的抗自由基物质, 具有很强的抗氧化性[4]和抗癌及预防心血管疾病等作用[5-6]。花青苷的抗氧化性与活性酚羟基有关, 酚羟基具有很强的抗氧化活性, 使花青苷具有清除各种活性氧自由基的能力[7-8]

植物花青苷生物合成途径属于类黄酮生物合成途径分支之一, 其生物合成过程不仅受结构基因的作用, 还受相关调节基因的影响[9-10]。在植物花青苷合成途径中, 结构基因直接参与花青苷和中间代谢产物的合成与贮藏, 主要包括查尔酮合酶基因(CHS)、查尔酮异构酶基因(CHI)、黄烷酮3-羟化酶基因(F3H)和类黄酮3′-羟化酶基因(F3′H)、NADPH依赖性二氢黄酮醇还原酶基因(DFR)、无色花青苷双加氧酶/花青苷合成酶基因(LDOX/ANS)和类黄酮-3-O-葡糖基转移酶基因(UF3GT)。与植物花青苷合成有直接关系的转录因子主要包括R2R3-MYB、MYC(bHLH)和WD40三类, 通过其单体或者复合体来调控结构基因的表达, 进而影响花色素的积累。

目前, 植物中花青苷的研究多集中在其组分研究上。本研究以6种不同着色程度的不结球白菜为试验材料, 比较其总花青苷含量, 采用DPPH自由基清除能力法(DPPH法)和铁离子还原能力法(FRAP法)来研究叶色差异的不结球白菜叶片的抗氧化活性, 并利用实时定量和半定量方法测定花青苷合成相关结构基因和调节基因的表达水平, 为进一步研究不结球白菜中花青苷的特性及生物合成机制提供理论基础。

1 材料与方法 1.1 材料

选用6种不结球白菜材料(图 1), 分别为深紫色的NJZX1-4(常规紫色可育系), 紫色的NJZX1-1(常规紫色不育系), 绿色的'苏州青'和NJZX1-0(由NJZX1-4经化学诱变后挑选出的可稳定遗传的绿色突变单株), 深紫色单株(NJZX2-2)和浅紫色单株(NJZX2-1)由NJZX1-4(母本)和NJZX1-0(父本)杂交后F1代经自交后所得F2代。

图 1 6种不结球白菜材料叶色的比较 Figure 1 Comparison of leaf color in six non-heading Chinese cabbage materials a.'苏州青''Suzhouqing'; b. NJZX1-0;c. NJZX2-1;d. NJZX1-1;e. NJZX2-2;f. NJZX1-4.

将种子用蒸馏水冲洗干净, 室温催芽3 d, 播种至穴盘。幼苗长到2叶1心时移至大棚, 待材料长至7叶期时取样, 并将所有样品置于-80 ℃保存备用。

1.2 花青苷的提取与测定

参照王小青等[11]的方法并略有改动。取新鲜功能叶片0.1 g用液氮研磨后, 加入1.5 mL酸化甲醇(含体积分数3%的HCl), 适当摇晃条件下室温浸提10 h; 常温10 000 r · min-1离心5 min, 然后取上清液经0.22 μm滤膜过滤, 备用。采用pH值示差法测定总花青苷含量, 具体步骤参照许玉超等[12]的方法。

1.3 不结球白菜叶片花青苷抗氧化活性测定

DPPH法:参照殷丽琴等[13]的方法测定DPPH自由基清除率, 生物学重复3次。

FRAP法:参照Benzie等[14]的方法测定FRAP值并略有改动。将FRAP工作液预热至37 ℃, 提取的甲醇粗液150 μL, 加入2 850 μL FRAP工作液, 暗室反应30 min后测定593 nm波长下的吸光值。以没食子酸溶液作为标准样品绘制标准曲线y=0.006 6 x+0.112 7(R2=0.969 6)。单位为μg · g-1。重复3次。

1.4 总RNA的提取与单链cDNA的合成

总RNA的提取参照RNA提取试剂盒使用说明书(TaKaRa)。单链cDNA的合成参照PrimeScript RT reagent Kit with gDNA Eraser反转录试剂盒(TaKaRa)。

1.5 实时荧光定量PCR

利用Beacon Designer v 7.9软件设计引物, 引物序列如表 1所示。Actin基因作为内参[15], 并通过普通PCR验证引物的特异性。RT-qPCR反应采用SYBR Premix Ex Taq试剂盒, 以稀释10倍的单链cDNA作为模板。体系共20 μL, 含SYBR Premix Ex Taq 10 μL, ddH2O 7.2 μL, 模板2 μL, 正、反引物各0.4 μL。生物学重复3次, 相对定量测定参照ΔΔCT[16]

表 1 引物序列 Table 1 Primer sequences in this study
引物Primer 序列Sequence(5′→3′) 用途Usage
BrcCHI-F/R TATTAAGGTGACGATGAAG/GAGAGAGCAAAGAGAATC RT-qPCR
BrcCHS-F/R ATCCAGACTACTACTTCC/GACTTCAACAACCACAAT RT-qPCR
BrcF3H-F/R CGAGCAGACTATCAATAG/ATATCTCTACTCATCTTTCTC RT-qPCR
BrcDFR-F/R CATAAGACAAGGACAGTAT/CGGAGATAGTAAGAATCG RT-qPCR
BrcANS-F/R ACCTTCATTCTACACAAC/AATCCTTACCTTCTCCTT RT-qPCR
BrcUFGT-F/R GTAATGTATCCGTGGTTAG/GGTAGAGGTTAAGAGGTT RT-qPCR
BrcGL3-F/R TCTATCTCTGCTTCTCAA/CTTCCTCGTCTTAATGTC RT-PCR
BrcEGL3.1-F/R GTGAAGAACTCAATAACTG/GTGAAGAACTCAATAACTG RT-PCR
BrcEGL3.2-F/R AGAGTGATATAGGAGAAGAT/TCGTATCATCAAGAATCG RT-PCR
BrcTT8-F/R CTGGAATCTACTCATCAC/GCATCTCATCTCTAACAA RT-PCR
BrcTTG1-F/R CACTCCACCATCATCTAC/GTCAAGAATCACAACCTTAT RT-PCR
BrcMYB90-F/R ACCCATTTGAGTAAGAAA/GGTATAAGAGCAAGGAAT RT-PCR
BrcMYB75-F/R GCTGTAATACCAAGATGA/AAGGAATAGAGGAATAACG RT-PCR
Actin-F/R GTTGCTATCCAGGCTGTTCT/AGCGTGAGGAAGAGCATAAC RT-PCR or RT-qPCR
1.6 半定量PCR

以单链cDNA作为模板, 体系20 μL:2×HiQPCR Mix 10 μL, 引物各1 μL, 模板1 μL, ddH2O 7 μL。反应程序为:96 ℃ 2 min; 96 ℃ 30 s, 57 ℃ 30 s, 72 ℃ 30 s, 28个循环; 72 ℃ 10 min。

1.7 数据处理

采用Microsoft Excel 2007和SPSS 20.0软件对数据进行统计分析, 以x±SD表示。

2 结果与分析 2.1 不结球白菜叶片的总花青苷含量

图 2可以看出:不结球白菜深紫色材料NJZX2-2和NJZX1-4叶中总花青苷含量较高, 分别为(693.0±50.6)和(801.5±57.4)μg · g-1, 极显著高于浅紫色材料NJZX1-1(P < 0.01);NJZX2-1叶中总花青苷含量为(279.7±56.5)μg · g-1, 且极显著低于NJZX1-1;绿色材料NJZX1-0和'苏州青'叶中总花青苷含量基本上为0。

图 2 6种不结球白菜材料叶片中总花青苷含量的比较 Figure 2 Comparison of total anthocyanin content of 6 materials in non-heading Chinese cabbage leaves 不同大写字母表示在0.01水平差异显著。下同。 Different capital letters indicate significant difference at 0.01 level. The same as follows.
2.2 不结球白菜叶片提取液的抗氧化活性

图 3可见:6种不结球白菜材料叶片提取液对DPPH自由基均具有良好的清除能力, DPPH自由基清除率为(49.31±3.91)%~(84.94±6.20)%, 变异系数为20.7%。6种材料中叶片提取液的DPPH自由基清除率由大到小依次为NJZX1-1、NJZX1-4、NJZX2-2、NJZX2-1、NJZX1-0、'苏州青', 且紫色材料叶片的DPPH自由基清除率极显著高于绿色材料叶片。叶片提取液的铁离子还原能力整体上是紫色叶片提取液高于绿色叶片(P < 0.05)。6种材料叶片提取液的FRAP值为(256.8±136.3)~(1 279.5±202.0)μg · g-1。其中, NJZX1-1叶片提取液的铁离子还原能力最强, 而NJZX2-1与NJZX1-0差异不显著。相关性分析表明, 不同叶色白菜叶片中总花青苷含量与铁离子还原能力极显著相关, 相关系数为0.646, 与DPPH自由基清除率也极显著相关, 相关系数为0.829。

图 3 不结球白菜叶片提取液的DPPH自由基清除率和FRAP值 Figure 3 DPPH free radical-scavenging rates and the values of FRAP of the extracts from non-heading Chinese cabbage leaves 不同小写字母表示在0.05水平差异显著。 Different small letters indicate significant difference at 0.05 level.
2.3 不结球白菜花青苷合成途径中结构基因的表达特性

图 4可见:花青苷合成途径中结构基因BrcF 3 HBrcDFRBrcANS的表达水平在紫色叶片中极显著高于绿色叶片, 且在6种材料中相对表达量与叶片总花青苷含量呈正相关。除BrcUFGT基因外其他5个结构基因在深紫色材料NJZX1-4和NJZX2-2中均有较高的表达量; BrcCHI基因在绿色的'苏州青'中的表达量显著高于紫色材料NJZX1-1, BrcCHS基因在'苏州青'中的表达量显著高于浅紫色材料NJZX2-1, 而BrcUFGT基因在所有材料中的表达均处于较低水平。

图 4 不结球白菜花青苷合成途径中结构基因的相对表达水平 Figure 4 Relative expression levels of the structural genes of the anthocyanin biosynthesis in non-heading Chinese cabbage
2.4 不结球白菜花青苷合成途径中调节基因的表达特性

7个调控花青苷的调节基因在6种材料叶片中的表达结果(图 5)显示:调节基因表达具有特异性。其中, BrcGL 3BrcEGL3.1 基因表现出相似的表达模式, 即在6种材料叶片中均有表达且在材料间差异不明显。此外, BrcMYB 75基因和BrcTTG1 基因在深紫色材料NJZX1-4叶片中有较高表达, 而BrcEGL 3.2基因和BrcMYB90基因在所有材料的叶片中均不表达; BrcTT8 基因在所有材料中表现不同的表达水平, 其表达量由大到小依次为NJZX2-2、NJZX1-4、NJZX1-1、NJZX2-1、'苏州青'、NJZX1-0, 与花青苷含量测定结果一致。

图 5 不结球白菜花青苷合成途径中调节基因的表达量 Figure 5 Expression level of the regulatory genes of the anthocyanin biosynthesis in non-heading Chinese cabbage
3 讨论

紫色白菜类叶片中所含色素大多为花青苷类化合物[17]。红叶芥菜、紫红色大白菜、红菜薹、紫色小白菜和紫结球甘蓝5种芸薹属新鲜叶片花青苷含量为130.0~719.0 μg · g-1[18]。本研究中, 紫色不结球白菜叶片中花青苷含量为0~801.5 μg · g-1, 绿色叶片基本不含花青苷; 其中, 紫色不结球白菜NJZX1-4叶片中花青苷含量明显高于红叶芥菜(719.0 μg · g-1)。紫色白菜叶片中DPPH自由基清除率和铁离子还原能力(FARP值)均显著高于绿色叶片, 且叶片花青苷含量与DPPH自由基清除率和铁离子还原能力基本呈正相关, 这与殷丽琴等[13]研究结果一致。

植物中花青苷生物合成受结构基因的作用。Gong等[19]研究发现F3H基因在红色紫苏叶片中表达, 而在绿叶材料中不表达, Sparvoli等[20]在葡萄中也发现类似结果。过量表达DFR1 基因, 可以增加转基因植株中花青苷的含量[21-22]。紫色羽衣甘蓝中DFRANS的表达明显高于绿色材料[23]。在本研究中, 结构基因BrcF3HBrcDFRBrcANS在紫色不结球白菜叶片中的表达极显著高于绿色叶片, 且其表达水平与不结球白菜叶片紫色着色程度呈正相关, 即叶片花青苷含量越高, 基因的表达量越高, 因此推测基因BrcF3HBrcDFRBrcANS为影响不结球白菜花青苷生物合成的关键基因。

双子叶植物花青苷的生物合成不但受结构基因的影响, 还受转录因子的调控作用[24]。植物花青苷生物合成调控因子主要有三大类, 包括MYB蛋白、bHLH蛋白和WD40蛋白, 3种蛋白之间均可发生相互作用, 进而形成二元复合物或者相互作用成MYB-bHLH-WD40三元复合物共同调控基因表达[25-26]。在拟南芥中, WD-repeat蛋白TTG1通过结合bHLH转录因子(GL3、TT8或EGL3)和R2R3-MYB转录因子(MYB75/PAP1、MYB90/PAP2、MYB113或MYB114)形成WD-repeat/Mybs/bHLH复合物来上调花青苷合成后期基因(DFRANSUF3GT)的表达[27-28]。本研究中, 我们发现在验证的7个调节基因中, BrcGL3BrcEGL3.1BrcTT8基因在绿色和紫色材料中均有表达, 其中BrcTT8基因在不同材料中的表达水平与其叶片着色程度相关, 即花青苷含量越多, BrcTT8表达量越高。另外, BrcMYB75和BrcTTG1在深紫色材料NJZX1-4叶片中有较高表达。本试验结果表明这些转录因子在很大程度上参与了叶片中花青苷的生物合成调控, 但其是如何通过调节结构基因进而调控花青苷的积累, 有待进一步研究。

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