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油菜素内酯诱导小白菜初生根不对称生长

  • 曹璐 1 ,
  • 付影 1 ,
  • 于旭东 1 ,
  • 蔡泽坪 , 1, * ,
  • 罗佳佳 1, 2 ,
  • 汤竹 1 ,
  • 黄晓薇 1
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  • 1. 海南大学热带农林学院,海南儋州 571737
  • 2. 中国热带农业科学院热带作物品种资源研究所/农业农村部热带作物种质资源利用重点实验室,海南儋州 571737
* 蔡泽坪(CAI Zeping),E-mail:

曹 璐(1998—),女,本科,研究方向:植物保护。

收稿日期: 2018-08-17

  要求修回日期: 2018-10-28

  网络出版日期: 2019-03-15

基金资助

国家自然科学基金项目(31660229)

海南大学科研启动基金项目(kyqd1620)

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版权所有,未经授权,不得转载、摘编本刊文章,不得使用本刊的版式设计。

Brassinosteroid Induces Asymmetric Growth of Primary Roots in Brassica chinensis L.

  • CAO Lu 1 ,
  • FU Ying 1 ,
  • YU Xudong 1 ,
  • CAI Zeping , 1, * ,
  • LUO Jiajia 1, 2 ,
  • TANG Zhu 1 ,
  • HUANG Xiaowei 1
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  • 1. Institute of Tropical Agriculture and Forestry, Hainan University, Danzhou, Hainan 571737, China
  • 2. Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences / Key Laboratory of Crop Gene Resources and Germplasm Enhancement in Southern China, Ministry of Agriculture and Rural Affairs, Danzhou, Hainan 571737, China

Received date: 2018-08-17

  Request revised date: 2018-10-28

  Online published: 2019-03-15

Copyright

Copyright reserved © 1981. Office of Acta Agronomica Sinica All articles published represent the opinions of the authors, and do not reflect the official policy of the Chinese Medical Association or the Editorial Board, unless this is clearly specified.

摘要

油菜素内酯(Brassinolide,BL)能诱导单子叶植物初生根发生不对称生长,而在双子叶植物中还未见报道。本试验通过外源施加不同浓度2,4-表油菜素内酯(2,4-Epibrassinolide,2,4-eBL)观察小白菜(Brassica chinensis L.)初生根生长状况。结果表明:2,4-eBL能诱导小白菜初生根发生不对称生长形成卷曲。随着2,4-eBL浓度的升高,根卷曲比例和曲率逐渐增大,同时向地性逐渐降低。试验发现外源施加2,4-eBL可诱导双子叶植物根不对称生长的现象,为研究油菜素甾醇(Brassinosteroids,BRs)在根生长发育中的作用提供新途径。

本文引用格式

曹璐 , 付影 , 于旭东 , 蔡泽坪 , 罗佳佳 , 汤竹 , 黄晓薇 . 油菜素内酯诱导小白菜初生根不对称生长[J]. 热带作物学报, 2019 , 40(3) : 468 -474 . DOI: 10.3969/j.issn.1000-2561.2019.03.008

Abstract

Brassinolide (BL) can induce asymmetric growth of primary roots of monocots, but has not been reported in dicots. The text used the seedlings of Brassica chinensis L. as the experimental materials to observe the growth of primary root by exogenous application of different concentrations of 2,4-epibrassinolide (2,4-eBL). The results showed that 2,4-eBL could induce asymmetric growth of the primary root of B. chinensis L. to form curls, while the curling ratio and curvature of the root growth gradually increased. For the first time, the test found that the external application of 2,4-eBL induced the asymmetric root growth of dicotyledonous plants, and provided a new way to study the role of Brassinosteroids (BRs) in root growth and development.

1979年Grove等[1]首次从欧洲油菜(Brassica napus L.)花粉中分离出油菜素内酯(Brassinolide, BL),至今已分离鉴定出70多种多羟基甾醇衍生物,统称油菜素甾醇(Brassinosteroids, BRs)[2]。在所有BRs中BL的生物活性最高[3,4]。BRs在根中合成并调控根的生长发育,影响根的伸长、不定根发生、侧根发育、根毛形成、根尖重力反应等[5,6,7,8,9]
BRs在植物体各器官中的分布存在显著差异,尤其在根中的含量甚微,从而导致其在根中的发现晚于下胚轴及植物体的其它部位。与此对应的是,根对BRs的反应要比植物体的其他部位敏感得多[10]。BRs最早的分离提纯来自于玉米(Zea mays),随后相继在拟南芥(Arabidopsis thaliana)、豌豆(Pisum sativum)和西红柿(Lycopersicon esculentum)的根中被发现[11,12,13]。研究证明BRs在调控根端分生组织(root apical meristem,RAM)分化以及根伸长的过程中扮演着重要角色[14]。在拟南芥中,BRs在极低浓度下(≤0.1 nmol/L)促进根的伸长[10],而在高浓度下(≥10 nmol/L)抑制[15,16,17]。BRs合成或信号受阻均会导致RAM变小和根长缩短[18]。BRs还在影响根的向地性上起关键作用,Soochul等[19]和Kim等[20]发现BRs可以增加玉米、拟南芥等不同物种主根的向地性曲率。在玉米中,当BL浓度为10-7 mol/L时向地性角度达到最大值;而在拟南芥中,当BL浓度为10-10~10-7 mol/L时,根向地性逐渐增强。
双子叶和单子叶植物根存在一定区别。其中,大多双子叶植物根为定根、根系为直根系,而单子叶植物根为不定根、根系为须根系[21]。BRs能够诱导单子叶须根系植物水稻(Oryza sativa)幼苗初生根发生不对称生长形成卷曲(coiling)和波浪形弯曲(wave)[22,23,24]。然而,关于BRs诱导双子叶直根系植物初生根不对称生长的研究还未见报道。本研究用2,4-表油菜素内酯(2,4- Epibrassinolide,2,4-eBL)处理双子叶直根系植物小白菜(Brassica chinensis L.),探究2,4-eBL调控小白菜根不对称生长、减弱初生根向地性的现象,为植物激素对根生长的研究提供新的见解。

1 材料与方法

1.1 材料

小白菜(Brassica chinensis L.)种子购自蔬菜物资公司,商品名称为绿领四月慢。2,4-eBL(code E-1641)购自sigma公司,用75%乙醇溶解并配制成1 mmol/L母液。

1.2 方法

1.2.1 种子灭菌 选择饱满且不开裂的种子,自来水浸泡30 min,在超净工作台上依次用75%乙醇和0.1%升汞分别浸泡30 s和7 min,无菌水浸洗5遍。
1.2.2 初生根向地性角度的测量 在超净工作台上,将灭好菌的小白菜种子接入2,4-eBL浓度梯度分别为0、2×10-11、2×10-9、2×10-7 mol/L的MS固体培养基中。每只试管接种1粒种子,重复10次,并于第3天测量初生根的向地性角度。
1.2.3 初生根主根长、曲率和卷曲比例的测量 在超净工作台上,将灭好菌的小白菜种子接入2,4-eBL浓度梯度分别为0、2×10-13、2×10-12、2×10-11、2×10-10、2×10-9、2×10-8、2×10-7 mol/L的MS固体培养基中。每瓶接种10粒种子,重复6次。第8 d测量主根长、曲率和卷曲比例。
1.2.4 培养条件 以上均为光照和黑暗培养,光照培养条件为:温度(25±2)℃,光强1000 lx,光周期为光照16 h/d,黑暗8 h/d;暗培养条件为:温度(25±2)℃,黑暗24 h/d。

1.3 数据分析

根长、曲率和向地性角度均采用Image J v1.50i软件(https://imagej.nih.gov/ij/index.html)测量。实验数据的统计和分析均采用SPSS 19.0统计软件,采用LSD检验和Duncan法进行数据差异显著性多重比较。

2 结果与分析

2.1 外源施加2,4-eBL对小白菜初生根向地性的影响

无论是光照培养还是暗培养,2,4-eBL对小白菜初生根向地性的作用2~3 d便能表现出来。浓度大于2×10-11 mol/L时,随着2,4-eBL浓度的升高,根尖向地性角度减小(图1A~图1H)。光培养下,2,4-eBL浓度为0时,根尖向地性角度为(70.9±10.4)°;浓度为2×10-11 mol/L时,根尖向地性角度与对照相比有显著差异;浓度为2×10-9 mol/L时,根尖向地性角度与对照相比有极显著差异;浓度为2×10-7 mol/L时,根尖向地性角度是对照的38.6%,有极显著差异(图1I)。暗培养下,2,4-eBL浓度为0时,根尖向地性角度为(74.4±10.6)°。浓度为2×10-11 mol/L及以上时,根尖向地性角度与对照相比有极显著差异;2,4-eBL浓度为2×10-7 mol/L时,根尖向地性角度是对照的43.5%(图1J)。可见,2,4-eBL对小白菜初生根向地性有减弱作用。
图1 2,4-eBL对小白菜初生根向地性的影响

A~D:光照培养3 d(A~D对应2,4-eBL浓度分别为0、2×10-11、2×10-9、2×10-7 mol/L);E~H:黑暗培养3 d(E~H对应2,4-eBL浓度分别为0、2×10-11、2×10-9、2×10-7 mol/L);I:光培养3 d初生根向地性角度;J:暗培养3 d初生根向地性角度;比例尺:1 cm。*表示与对照相比存在显著差异(p<0.05);**表示与对照相比存在极显著差异(p<0.01)。

Fig. 1 Effect of 2,4-eBL on the angle of primary root tip to ground of Brassica chinensis L.

A-D: 3rd day under light illumination (A-D, the 2,4-eBL concentration was 0, 2×10-11, 2×10-9, 2×10-7 mol/L); E-H: 3rd day under dark illumination (E-H, the 2,4-eBL concentration was 0, 2×10-11, 2×10-9, 2×10-7 mol/L); I: light culture of the primary root to the earth angle; J: dark culture of the primary root to the earth angle. Scale: 1 cm. * indicates that there is a significant difference with the control group (p<0.05); ** indicates that there is a highly significant difference with the control group (p<0.01).

2.2 外源施加2,4-eBL对小白菜初生根不对称生长的影响

无论是光照培养还是暗培养,外源施加2,4-eBL能诱导小白菜初生根不对称生长形成卷曲。光培养下,2,4-eBL浓度为0时,初生根卷曲的曲率是(0.17±0.03)mm-1,卷曲比例为(3.3± 2.9)%;当浓度为2×10-13 mol/L时,卷曲的比例为(12.97±3.23)%,是对照的3.89倍,具有极显著差异(p<0.01)。对于初生根卷曲曲率而言,当浓度小于2×10-10 mol/L时,初生根卷曲曲率随着2,4-eBL浓度的升高缓慢上升,当浓度大于2×10-10 mol/L时,初生根卷曲曲率随着2,4-eBL浓度的升高迅速上升。对于初生根卷曲比例而言,当浓度小于2×10-9 mol/L时,初生根卷曲比例随着2,4-eBL浓度的升高缓慢上升,当浓度大于2×10-9 mol/L时,初生根卷曲比例随着2,4-eBL浓度的升高迅速上升;当浓度为2×10-7 mol/L时卷曲的曲率和比例达到最大值,分别为(0.65± 0.06)mm-1和(95±5)%,是对照的3.82和28.53倍(图2A~图2F图3C图3E)。暗培养下,2,4-eBL浓度为0时,初生根卷曲的曲率是(0.20±0.04)mm-1,卷曲比例为(3.7±3.2)%;2,4-eBL浓度为2×10-10 mol/L时,根卷曲的曲率为(0.24± 0.04)mm-1,是对照的1.2倍,差异显著(p<0.05);而卷曲比例为(24.57±1.87)%,是对照的6.59倍,差异极显著;当浓度小于2×10-9 mol/L时,初生根卷曲曲率和卷曲比例随着2,4-eBL浓度的升高缓慢上升,当浓度大于2×10-9 mol/L时,初生根卷曲曲率和卷曲比例随着2,4-eBL浓度的升高迅速上升;浓度为2×10-7 mol/L时卷曲的曲率和比例达到最大值,分别为(0.76±0.14)mm-1和(98.23± 3.01)%,是对照的3.80和26.34倍,有极显著差异(图2G~图2L图3D图3F)。
图2 2,4-eBL诱导小白菜初生根发生卷曲

A~F: 光照培养8 d(A~F所对应的2,4-eBL浓度分别为0、2×10-11、2×10-10、2×10-9、2×10-8、2×10-7 mol/L);G~L: 黑暗培养8 d(G~L所对应的2,4-eBL浓度分别为0、2×10-11、2×10-10、2×10-9、2×10-8、2×10-7 mol/L)。比例尺:1 cm。

Fig. 2 2,4-eBL induces the primary root curl of Brassica chinensis L. seedling

A-F: 8th day after illumination (the 2,4-eBL concentration of A-F is 0, 2×10-11, 2×10-10, 2×10-9, 2×10-8, 2×10-7 mol/L, respectively); G-L: 8th day of darkness (the 2,4-eBL concentration of G-L is 0, 2×10-11, 2×10-10, 2×10-9, 2×10-8, 2×10-7 mol/L, respectively). Scale: 1 cm.

2,4-eBL对小白菜幼苗初生根长度也具有一定的影响。光培养下,2,4-eBL浓度为0时,初生根长为(55.2±17.9)mm;当浓度为2×10-7 mol/L时,初生根长为(23.63±11.39)mm,是对照的42.8%,根长明显缩短,差异极显著(图3A)。暗培养下,2,4-eBL浓度为0时,初生根长为(67.1±17.7)mm;2,4-eBL浓度为2×10-13 mol/L时,初生根长为(94.26±27.82)mm,是对照的1.4倍,差异显著;浓度为2×10-12 mol/L时,初生根长为(87.35± 15.13)mm,是对照的1.3倍,差异极显著;浓度为2×10-8~2×10-7 mol/L时,初生根长分别为(50.47±7.57)mm和(37.86±11.68)mm,是对照的75.2%和56.4%,差异均极显著(图3B)。浓度相同的2,4-eBL暗培养下初生根长普遍大于光培养(图3A图3B)。可见,2,4-eBL可诱导小白菜初生根发生不对称生长以及能影响初生根的根长。
图3 2,4-eBL对小白菜初生根长、根向地性曲率及卷曲比例的影响

A:光培养8 d初生根长;B:暗培养8 d初生根长;C:光培养8 d初生根曲率;D:暗培养8 d初生根曲率;E:光培养8 d初生根卷曲比例;F:暗培养8 d初生根卷曲比例。*表示与对照相比存在显著差异p<0.05;**表示与对照相比存在极显著差异 p<0.01。

Fig. 3 Effects of 2,4-eBL on primary root length, primary root curvature and curling ratio of Brassica chinensis L.

A: The primary root length of light culture; B: The primary root length of dark culture; C: The primary root curvature of light culture; D: The primary root curvature of dark culture; E: The proportion of the primary root curling under the light culture; F: The proportion of the primary root curling under dark culture. * indicates that there is a significant difference with the control group p<0.05; ** indicates that there is a highly significant difference with the control group p<0.01.

3 讨论

BRs能够影响植物的光形态建成[25]。为了探究光照是否参与了BRs导致的根不对称生长,本试验通过外源添加不同浓度2,4-eBL,分别在光暗2种培养条件下,观察小白菜初生根生长状况。
当2,4-eBL浓度为0时,小白菜主根也会出现极少量(<4%)卷曲现象。Mullen等[26]发现重力刺激和根的接触刺激可以使拟南芥初生根发生卷曲或弯曲现象。Jiang等[27]发现水稻根接触到培养瓶的底部时,主根会发生卷曲,如果培养瓶中的介质足够深以致主根不能接触瓶底,主根不会发生卷曲。杨文等[23]发现接触刺激可使2,4-eBL处理的水稻初生根发生不对称生长的比例显著上升。由此可见,接触刺激对根的不对称生长具重要作用。
BRs能使单子叶植物初生根发生不对称生长,杨文等[22]发现2,4-eBL能够使水稻初生根发生不对称生长形成卷曲和波浪形弯曲,当2,4-eBL浓度为2×10-13~2×10-9 mol/L时根发生不对称生长的比例与对照无显著差异,当2,4-eBL浓度达到2×10-8~2×10-7 mol/L根不对称生长比例开始增大,且均与对照相比有极显著差异。而本文也研究了浓度分别为0、2×10-13、2×10-12、2×10-11、2×10-10、2×10-9、2×10-8、2×10-7 mol/L的2,4-eBL对小白菜初生根不对称生长的影响,发现浓度越高,小白菜初生根不对称生长越明显。可见BRs不论是对单子叶植物还是双子叶植物,都能够诱导其根发生不对称生长。
除BRs之外,乙烯(Ethylene, Eth)和茉莉酸(Jasmonic acid, JA)也能够诱导植物根发生不对称生长。Woods等[28]发现外源施加不同浓度的Eth可以诱导番茄幼苗根发生卷曲,卷曲程度取决于Eth浓度,并且添加银离子能阻止此现象的发生。Cai等[24]发现2,4-eBL诱导水稻初生根不对称生长的作用能被Eth抑制剂氨基氧乙酸(aminooxyacetic acid, AOA)、CoCl2和银离子抑制,从而证明Eth可参与油菜素内酯调控的水稻初生根不对称生长。Jiang等[27]报道自然生长的野生型水稻初生根不会发生卷曲,当外源施加0.1 μmol/L JA时,可诱导5%的初生根卷曲,0.5 μmol/L JA能诱导10%的水稻根发生卷曲。然而BRs在诱导双子叶植物根发生不对称生长的过程与Eth和JA是否存在联系还有待进一步研究。
BRs还能影响初生根的向地性反应以及根长。Kim等[29]发现BRs在功能上与生长素(Auxin, IAA)结合调控植物根部向重力性。不同浓度的BL对玉米根的向地性影响不同,BL浓度范围在10-9~10-5 mol/L时,会增强根的向地性。在浓度为10-7 mol/L时向地性角度达到最大值[19]。而本文研究了浓度为0、2×10-11、2×10-9、2×10-7 mol/L 2,4-eBL对小白菜初生根向地性反应的影响,结果表明在这些浓度下,BRs对向地性反应有减弱作用。且2,4-eBL浓度为2×10-11、2×10-9、2×10-7 mol/L时,小白菜初生根的向地性角度逐渐减小,而不对称生长的程度逐渐增大。根的向地性与不对称生长之间有何种联系还不得而知。

The authors have declared that no competing interests exist.

作者已声明无竞争性利益关系。

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