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天女木兰(Magnolia sieboldii K. Koch)又名小花木兰,为木兰科(Magnoliaceae)木兰属(Magnolia)的落叶小乔木,是国家三级濒危植物。天女木兰在组培过程中外植体褐化非常严重,严重影响了其组培成功率。木本植物与草本植物相比褐化现象更为严重,其原因是木本植物含较多的酚类化合物。多酚氧化酶(PPO)是末端氧化酶,在正常情况下植物体酚类物质与醌类分布在细胞内不同区域,酚类物质分布在液泡内,PPO分布在质体和细胞质中与膜结合呈潜伏状态,当外植体被切割后膜结构遭到破坏,PPO与酚类物质接触,在外植体伤口处发生氧化作用,酚类物质被氧化成醌类物质,醌类物质再经非酶促反应聚合形成褐色物质,并对植物产生毒害作用[1-5]。为了控制外植体褐化,人们在培养基中添加抗褐化剂达到预防褐化目的,比如:维生素C、柠檬酸、半胱氨酸、聚乙烯吡咯烷酮和活性炭等。目前,有少量使用抗褐化剂抑制天女木兰组培褐化方法的研究报道[6-7],而关于抗褐化剂控制天女木兰外植体褐化机理的研究还未见报道。本文以天女木兰芽作为外植体,在培养基中分别添加维生素C、柠檬酸和聚乙烯吡咯烷酮三种类型抗褐化剂,在组织培养过程中定期取样,利用高效液相色谱仪测定芽外植体中主要酚酸含量动态变化,确定引起天女木兰褐化现象的主要酚酸种类,从外植体褐化率及外植体主要酚酸含量动态变化两方面,比较三种抗褐化剂的抗褐化效果,确定酚酸种类与褐化的关系,为解决天女木兰组培褐化问题及揭示不同类型抗褐化剂的作用机理提供一定理论依据。
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于4月初采集天女木兰成年树上一年生枝条,放置在实验室进行水培8~10 d,待芽萌动膨大时剪取顶芽和侧芽,芽长0.5~1.0 cm,用洗洁精浸泡20 min,流水冲洗2 h。在超净工作台内将芽放入质量分数为75%的乙醇溶液中消毒30 s,用无菌水冲洗3次,然后用0.1%氯化汞处理7 min,无菌水冲洗5次,接种。
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在B5培养基中分别添加不同浓度维生素C(以下简称VC)、柠檬酸(以下简称CA)和聚乙烯吡咯烷酮(以下简称PVP)三种抗褐化剂,其余添加成份相同,分别添加0.5 mg·L-1六苄基腺嘌呤(6-BA)、0.3 mg·L-1吲哚丁酸(IBA)、蔗糖30 g·L-1,调pH 5.6~5.8。试验设一个对照(CK)和三个不同浓度(T1、T2和T3)处理,每个处理培养30瓶,重复3次。各处理添加抗褐化剂浓度详见表 1。培养温度25℃,光照1 500~2 000 lx,培养30 d统计外植体褐化率。褐化率计算方法为:褐化率=褐化瓶数/培养瓶数×100%。试验采用单因素方差分析及多重比较,利用Spass 18.0版软件对褐化率进行统计分析。
表 1 不同浓度抗褐化剂处理对外植体褐化的影响
Table 1. Effect of explants browning treated by anti-browning agents with deferent levels
抗褐化剂种类
Anti-browning agent type处理
Treatment添加浓度
Added concentration/(mg·L-1)接种瓶数
Vaccination bottle quantity褐化率
Browning rate/%(30 d)褐化程度
Browning degreeCK 0 30 52.2±1.69e +++ VC T1
T2
T3250
500
75030
30
3016.7±1.49ab
12.2±0.994a
48.9±1.69e+
+
+++CA T1
T2
T3100
300
50030
30
3036.7±1.15d
26.7±1.25c
27.8±0.71c++
++
++PVP T1
T2
T3500
1000
150030
30
3026.7±1.25c
18.9±0.82b
17.8±0.821b++
+
+表中褐化率一栏数据为褐化率平均值±标准误,不同小写字母表示差异极显著(α=0.01)。
褐化程度分轻、中和重度三级,分别用“+”、“++”和“+++”表示。
Values represent the means ±SE, and different small letters within the column indicated significance atα=0.01 level.
Browning degree is categorized into light, moderate, and severe levels, represented by +”, “++”and “+++”, respectively. -
接种10 d后开始取样,取样时间为10 d、20 d和30 d,选取具有代表的芽外植体,液氮冷冻,存放于-80℃超低温冰柜中保存备用。
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参考Rosa等[8]发表的方法略加改动。称取冷冻样品2.0 g,加液氮研磨,用16 mL 60% 乙醇超声波提取30 min,重复提取3次,过滤,滤液合并。用旋转蒸发仪35℃低压蒸出乙醇剩水相,用6 mol·L-1盐酸溶液调水相pH至2.0,用30 mL乙酸乙酯萃取3次,合并酯相。在35℃下浓缩至干,残渣用60%甲醇溶解,定容至5 mL,用0.45μm滤膜过滤,上样检测。
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高效液相色谱仪(型号LC-20A,岛津公司生产);二极管阵列检测器(型号SPD-M20A);InertSustainC18色谱柱(规格4.6 mm ×250 mm, 5 μm)。使用A和B双泵系统,流速0.8 mL·min-1, 柱温30℃。流动相A为1%(体积分数)乙酸水溶液,流动相B为1%乙酸甲醇溶液;采用梯度洗脱,洗脱梯度:起始浓度10% B; 0~15 min, 18% B; 15~35 min, 25% B; 35~45 min, 35% B; 45~60 min, 50% B; 60~65 min, 95% B。甲醇和乙酸均为色谱纯,咖啡酸、绿原酸和对香豆酸纯度>99%(Sigma公司生产)。定量方法采用孙洪圳[9]等介绍的方法进行,每个样品重复三次进样测定,测定结果取平均值。
抗褐化剂对天女木兰芽外植体褐化与酚酸氧化的影响
Effects of Browning Inhibitors on Bud Explants Browning and Phenolic Acids Oxidation of Magnolia sieboldii K. Koch
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摘要:
目的 确定引起天女木兰褐化现象的酚酸种类,筛选出最佳抗褐化剂及使用最适浓度。 方法 在B5培养基中分别添加各种抗褐化剂,芽外植体培养30 d后计算出褐化率,对褐化率结果进行统计分析,并比较三种抗褐化剂的抗褐化效果;另外,在组培过程中定期取样,利用HPLC测定芽外植体中咖啡酸、绿原酸和对香豆酸含量变化。 结果 表明:天女木兰芽外植体褐化过程中咖啡酸和绿原酸含量下降幅度较大,而对香豆酸含量下降幅度较小,说明咖啡酸和绿原酸容易被氧化,而对香豆酸较为稳定;三种抗褐化剂控制褐化现象发生的最佳效果排序为VC>PVP>CA;尽管PVP控制酚酸氧化效果不如CA,但是预防褐化效果确强于CA,其原因是由于二者抗褐化机理不同所致;VC使用的最适浓度为500 mg·L-1,如果超过此浓度会导致外植体褐化率增加;PVP最适浓度为1 000~1 500 mg·L-1,CA最适浓度为300 mg·L-1。 结论 天女木兰芽外植体褐化底物是咖啡酸和绿原酸,而与对香豆酸无关;VC、PVP和CA三种抗褐化剂抗褐化机理各不相同,综合比较VC抗褐化效果最好,其次是PVP,CA排在最后。 Abstract:Objective To identify the types of phenolic acids that result in bud explants browning of Magnolia sieboldii and determine the most effective anti-browning agent at an optimum concentration. Method Bud explants were cultured in B5 medium for 30 days. At the beginning, three kinds of anti-browning agents were added separately to the B5 medium. The browning rates were calculated and analyzed. Then the effects of the three inhibitors on anti-browning were compared on the basis of the browning rates. In addition, the content variations of caffeic acid, chlorogenic acid, and p-coumaric acid in the bud explants were measured with HPLC using samples regularly selected during tissue culturing. Result The results showed that the contents of caffeic acid and chlorogenic acid decreased sharply while the content of p-coumaric acid experienced a slight decrease, proving that caffeic acid and chlorogenic acid were more likely to be oxidized than p-coumaric acid. Moreover, the effects of the three inhibitors on anti-browning were sorted in a decreasing order of VC, PVP, and CA. Although PVP was inferior to CA with respect to controlling phenolic acid oxidation, its anti-browning effect was more efficient than CA. This result was explained by their different mechanisms for anti-browning. Lastly, the optimal concentration for VC was 500 mg·L-1, and a higher concentration would result in a greater browning rate of the bud explants. Respective optimal concentrations for PVP and CA were 1 000~1 500 mg·L-1 and 300 mg·L-1. Conclusion The browning substrates in bud explants of M. sieboldii are caffeic acid and chlorogenic acid rather than p-coumaric acid. VC, PVP, and CA have distinguishable anti-browning mechanisms and the anti-browning effects of them will decrease gradually. -
Key words:
- Magnolia sieboldii
- / explant
- / browning inhibitor
- / phenolic acid oxidation
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表 1 不同浓度抗褐化剂处理对外植体褐化的影响
Table 1. Effect of explants browning treated by anti-browning agents with deferent levels
抗褐化剂种类
Anti-browning agent type处理
Treatment添加浓度
Added concentration/(mg·L-1)接种瓶数
Vaccination bottle quantity褐化率
Browning rate/%(30 d)褐化程度
Browning degreeCK 0 30 52.2±1.69e +++ VC T1
T2
T3250
500
75030
30
3016.7±1.49ab
12.2±0.994a
48.9±1.69e+
+
+++CA T1
T2
T3100
300
50030
30
3036.7±1.15d
26.7±1.25c
27.8±0.71c++
++
++PVP T1
T2
T3500
1000
150030
30
3026.7±1.25c
18.9±0.82b
17.8±0.821b++
+
+表中褐化率一栏数据为褐化率平均值±标准误,不同小写字母表示差异极显著(α=0.01)。
褐化程度分轻、中和重度三级,分别用“+”、“++”和“+++”表示。
Values represent the means ±SE, and different small letters within the column indicated significance atα=0.01 level.
Browning degree is categorized into light, moderate, and severe levels, represented by +”, “++”and “+++”, respectively. -
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