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蔬菜徒长苗的形态及生理特征研究进展

2017-01-21王红飞尚庆茂农业部园艺作物生物学与种质创制重点实验室中国农业科学院蔬菜花卉研究所环渤海湾地区设施蔬菜优质高效生产协同创新中心北京100081

中国蔬菜 2017年7期
关键词:胚轴徒长幼苗

王红飞 尚庆茂(农业部园艺作物生物学与种质创制重点实验室,中国农业科学院蔬菜花卉研究所,环渤海湾地区设施蔬菜优质高效生产协同创新中心,北京100081)

蔬菜徒长苗的形态及生理特征研究进展

王红飞 尚庆茂*
(农业部园艺作物生物学与种质创制重点实验室,中国农业科学院蔬菜花卉研究所,环渤海湾地区设施蔬菜优质高效生产协同创新中心,北京100081)

蔬菜集约化育苗以多孔连体式穴盘为容器,密度高,根系发育空间小,基质缓冲能力弱,幼苗极易徒长。徒长苗形态及生理代谢迥异于正常苗,表现为下胚轴及节间显著伸长,叶片开展度增大、叶片变薄,根冠比降低,组织含水量提高,对生物和非生物逆境的适应性减弱等。本文就蔬菜徒长苗的形态特征、开花习性、抗性表达、生理代谢及相关防控技术等进行了简要综述,旨在为蔬菜徒长苗的防控及相关技术的开发提供参考。

徒长苗;形态特征;开花习性;生理特征;环境因子

蔬菜集约化育苗以多孔连体式穴盘为容器,以人工混配轻型基质替代土壤,具有节种、节能、省工,适于规模化、标准化生产,便于机械化操作等优点,但在实际生产过程中存在幼苗密度大、植株间相互荫蔽等问题,容易形成徒长苗。此外,为满足周年生产需要,蔬菜集约化育苗常在气候不适宜的季节进行(尚庆茂,2011),夏季的阴雨高温天气、冬季的雾霾天气频繁出现,这种弱光、高温、高湿条件常会导致幼苗徒长,不利于壮苗的育成和优质丰产栽培(甘小虎 等,2012 a,2012 b)。

幼苗徒长已成为当前的研究热点,国内外众多学者对幼苗徒长机制进行了研究,认为植物激素在幼苗徒长过程中发挥了关键作用。IAA、GA是较早发现的两类植物激素,植物体内IAA、GA含量升高,幼苗株高显著增加,除株高外的其他表型特征及幼苗体内生理代谢等亦发生变化(Gray et al., 1998;Koini et al.,2009;Sun et al.,2012;Procko et al.,2014;Song et al.,2015)。本文就蔬菜徒长苗的形态特征、开花习性、生理特征、环境因子与徒长苗的关系及幼苗徒长防控技术进行综述,旨在为蔬菜徒长苗的制御及相关技术的开发提供参考。

1 蔬菜徒长苗的形态特征

1.1 表型特征

徒长是指蔬菜幼苗因生长条件不协调而产生的茎叶发育过旺的现象(单永辉,2006)。徒长苗主要是由于纵向生长加速引起的(梁镇林,2000),株高显著高于正常幼苗。徒长苗的株高变化主要是由下胚轴长度变化引起的(周学超,2010),下胚轴中段的长度显著高于上段和下段(Xiao et al.,2014,2016)。此外,徒长苗的茎粗降低,株高/茎粗的比值升高(侯兴亮 等,2002;王学文 等,2009;武晓玲 等,2014);徒长苗的叶片颜色变淡,比叶面积增加,叶片厚度显著降低(侯兴亮 等,2002;王学文 等,2009;周学超,2010);叶柄变长,促使叶片靠上生长,叶柄与胚轴夹角变大,呈现出偏下生长的特性(Zanten et al.,2009;Delker et al.,2014;Fankhauser & Batschauer,2016)。此外,徒长苗的根系吸收能力也受到影响,根系长度、侧根数量显著降低,根冠比、壮苗指数分别降至对照的66.67%和48.52%(武晓玲 等,2014;Prockoet al.,2014)。

1.2 细胞及亚细胞结构特征

徒长苗根茎叶等器官的形态变化,主要是由这些器官的组成细胞变化引起的,徒长苗的下胚轴、叶片在细胞水平和亚细胞水平均发生显著变化。徒长苗的下胚轴细胞长度显著高于正常苗(Gendreau et al.,1997),且下胚轴中段细胞长度显著高于上段和下段(Xiao et al.,2016)。徒长苗的下胚轴细胞呈矩形,表皮细胞表面较为平滑,细胞排列较为疏松,而正常幼苗的下胚轴细胞则为椭圆形,表皮细胞较小,呈多边形,沿纵轴紧密排列(Qin et al.,2012)。徒长苗叶片栅栏组织和海绵组织厚度均有所降低,但栅栏组织降低幅度大,细胞变短,排列疏松,而正常苗栅栏组织细胞排列整齐,呈长柱形(王学文 等,2009;周学超,2010)。在亚细胞结构水平,徒长苗下胚轴细胞中的叶绿体变长,基粒和基质片层数量减少,线粒体数量增多,淀粉粒消失(胡宏敏,2012);叶肉细胞液泡内含物增多,叶绿体在细胞内呈不规则分布,线粒体内含物减少,部分线粒体出现膜破裂、空泡化和解体的现象(周学超,2010)。

2 蔬菜徒长苗的开花习性

蔬菜徒长苗营养生长旺盛,消耗了大量营养物质,导致组织C/N比例发生变化,进而显著影响开花结实进程(Casal,2013)。前人研究表明,徒长苗的开花时间提前,且开花时间与抽生叶片数呈显著正相关(Botto & Smith,2002;Blázquez et al.,2003;Balasubramanian et al.,2006)。一般情况下,拟南芥(Col)正常苗于第17片莲座叶片展开时进行抽薹开花,而徒长苗提前至第10片莲座叶片展开时就抽薹开花了(Koini et al.,2009)。黄瓜徒长苗开花习性也发生变化,第1雌花节位显著升高,开花时间较对照晚2~5 d(明村豪 等,2011)。拟南芥徒长苗与黄瓜徒长苗在开花习性方面的差异,可能是由于物种、生长条件不同造成的。

3 蔬菜徒长苗的生理特征

3.1 水分代谢

蔬菜徒长苗的根系长度、侧根数量下降,根系活力受到抑制,由0.4 mg·g-1·h-1降低至0.2 mg·g-1·h-1,导致植物水分代谢及以水分代谢为载体的矿质营养代谢能力降低(周艳虹 等,2004;周学超,2010)。与正常苗相比,徒长苗气孔开度降低,导致蒸腾速率下降,水分流失受到抑制,组织含水量增加,为正常苗的103.88%(侯兴亮 等,2002;王学文 等,2009)。

3.2 光合代谢

徒长苗的叶绿素和类胡萝卜素含量显著下降,捕光能力降低,细胞色素质琨(PQ)、细胞色素蛋白(Cyt)和铁氧还素(Fd)等电子传递链组分含量显著下降,光反应受到抑制;此外,Rubisco羧化酶活性降低,导致叶肉细胞对CO2的利用能力下降,暗反应受影响,碳水化合物合成量降低,植株干物质积累量减少(周艳虹 等,2004;王祥宁 等,2007;明村豪 等,2011)。

3.3 抗逆代谢

徒长苗叶面积、下胚轴长度显著增加,细胞膨大,细胞壁厚度降低,导致植物组织韧性降低,对生物和非生物逆境的适应能力降低(Derbyshire et al.,2007;Irshad et al.,2008)。

3.3.1 非生物胁迫 蔬菜徒长苗可溶性固形物、可溶性糖、可溶性蛋白含量降低,渗透调节能力下降,不利于植物抵御高渗、低温等非生物胁迫(徐磊 等,2009;明村豪 等,2011)。此外,徒长苗体内花青素、芥子油甙、酚类物质等次级代谢产物显著降低(Izaguirre et al.,2006;Moreno et al.,2009;Xie et al.,2016)。花青素可以释放H+,清除氧自由基,避免光抑制、膜脂过氧化等现象出现,从而保护膜系统的完整性,提高对高温、低温、干旱、强光等非生物胁迫的适应能力(Lorenc-Kukuła et al.,2005;Albert et al.,2009)。

3.3.2 生物胁迫 徒长苗叶片及胚轴表面的凸起、绒毛、刺瘤等保护结构密度降低。番茄徒长苗绒毛数量减少,导致大量螨类害虫在植株上繁殖并刺吸植物茎叶,受害叶片前期产生黄褐斑,后期失绿脱落(Nihoul,1993;Roberts & Paul,2006)。

番茄灰霉菌和葡萄孢属真菌等病原菌侵染植物组织后,能激发活性氧产生,而活性氧清除能力较差的徒长苗受到致病菌青睐,发病率显著高于正常苗(Iriti et al.,2004;Segmüller et al.,2008;Zhang et al.,2013),黄瓜徒长苗的白粉病发病率约为正常苗的2.5倍(Wang et al.,2010)。芥子油甙和酚类物质具有挥发性,一方面能趋避有害昆虫,另一方面能吸引有害昆虫的捕食者和寄生性天敌,以防虫害发生(Roberts & Paul,2006;Xia et al.,2009;Wang & Wu,2013)。番茄徒长苗中绿原酸、芸香苷等酚类物质含量降低,导致植株受毛毛虫啃食严重(Jansen & Stamp,1997)。

徒长苗体内生长素(IAA)、赤霉素(GA)、茉莉酸(JA)、水杨酸(SA)等含量变化显著(Feng et al.,2008;Ballaré,2011;Agrawal et al.,2012;Fu et al.,2012),与细胞膨大相关的IAA和GA含量显著增加,与植物抗逆能力相关的JA、SA含量降低。GA能诱导JA信号传导关键因子DELLA蛋白泛素化降解,导致JA信号转导中断,JA能促使PR蛋白的合成量提高,并介导受病原菌侵染和有害昆虫啃食细胞的程序性死亡,从而提高植株抵御生物胁迫的能力(Hou et al.,2010;Ballaré et al.,2012;Campos et al.,2016)。

4 环境因子与蔬菜幼苗徒长

4.1 单一环境因子

光照强度与幼苗徒长程度呈负相关,光照越弱,徒长越严重。当光照强度降低至对照(1 100~1 300 μmol·m-2·s-1)的60%~70%时,黄瓜幼苗便开始徒长,徒长苗高度达到对照的1.10倍;光照强度继续降至对照的30%~40%时,徒长苗高度为对照的1.23倍(明村豪 等,2011)。红光与远红光对幼苗徒长的调控作用相反,红光抑制,远红光促进,在R∶FR比值较低的条件下,幼苗徒长,下胚轴长度超出对照1倍(Hersch et al.,2014)。昼夜节律作为重要的光信号因子,对植物的生长发育起着重要调控作用,徒长苗下胚轴长度随黑暗时间延长而增加,极夜条件下徒长苗下胚轴长度为极昼条件下的6倍(Niwa et al.,2009)。

作为影响植物生长发育的另一重要环境因子,温度在一定范围内升高时,能促进植物下胚轴伸长,但当温度超过植物适宜生长范围后,反而抑制下胚轴伸长(Dafny-Yelin et al.,2008;Sun et al.,2012)。 在温光适宜的范围内,水分充足有利于壮苗的培育,但水分含量过高时,容易造成幼苗徒长;水分含量过低,容易形成老化苗(王娟 等,2002)。

4.2 复合环境因子

温、光、水作为植物赖以生存的环境条件,既能单独发挥作用,又能协同调控植物生长(Franklin,2009)。在低温条件下,光照强度在0~100 μmol·m-2·s-1范围内增加时,能显著抑制幼苗下胚轴伸长;但当温度升高至27 ℃,光照强度在0~1 μmol·m-2·s-1范围内变化时,则抑制下胚轴伸长,但光照强度在1~100 μmol· m-2·s-1范围内变化时,能促进下胚轴伸长(Johansson et al.,2014)。研究表明,基质含水量过高,能引起蔬菜幼苗徒长,在弱光条件下徒长尤为严重(毛炜光 等,2007;徐磊 等,2009)。在调控幼苗生长的过程中,温度和水分互作显著,二者协同作用条件下,幼苗生长量增加,徒长明显(Vile et al.,2012)。

5 蔬菜幼苗的徒长防控技术

近年来,国内外众多学者对蔬菜幼苗徒长机理进行了研究,并取得了长足进展,研究结果表明,光敏色素互作蛋白PIFs在幼苗徒长过程中发挥关键作用(Casal,2013;Procko et al.,2014)。PIFs是一类bHLH转录因子,通过促进植物激素合成,引起幼苗徒长(Tao et al.,2008;Stavang et al.,2009;Franklin et al.,2011;Delker et al.,2014)。随着下胚轴伸长机理逐渐明确,生产管理人员加强了蔬菜生长敏感期的环境管理,并针对调控下胚轴伸长的关键位点,研发了相应的延缓型植物生长调节剂,对幼苗徒长防控效果明显(Heins et al.,2000;宫万祥和丁克友,2007)。此外,许多行业专家试图通过机械刺激防控蔬菜幼苗徒长,以替代植物生长调节剂在蔬菜生产中的地位,推动绿色、有机蔬菜的生产(Garner & Bjorkman,1996)。

5.1 环境管理

蔬菜幼苗生长早期对环境条件敏感,外界的弱光、高温及高湿等环境条件极易引发幼苗的徒长,此时要加强对环境的管理。

光照强度是影响幼苗生长的重要因素,连续的阴雨及雾霾等障碍天气的出现,常会导致幼苗徒长。生产过程中,一般采用透光率较好的无滴膜及增加后墙反光幕等方法,增加光照强度,防止幼苗徒长(杨艳春,2013)。此外,在温室内增加人工光源,可有效抑制下胚轴伸长,促进植株根系生长,提高幼苗的抗逆性(祝聪宇 等,2017)。

植物对温度变化敏感,温度稍高便可引起幼苗徒长,栽培管理过程中,要注意及时放风,以降低室内温度,夜间可适当升温,减小昼夜温差,可有效抑制幼苗徒长(Berghage,1998)。

秋冬季光照相对较弱,要严格把控浇水量和浇水时间,定植前浇透水,定植后和缓苗期浇小水(杨艳春,2013),以防止幼苗徒长。

5.2 植物生长调节剂

利用植物生长调节剂防控幼苗徒长是一种简单而有效的方法,目前已在蔬菜幼苗培育过程中得到了广泛应用(王娟,2006)。生产上常用的植物生长调节剂主要包括矮壮素(chlorocholine chloride,CCC)、烯效唑(U-niconazole,S3307)、多效唑(paclobutrazol,PP333)、比久(B9)等,处理方法主要包括浸种、种子包衣、叶面喷施、土壤或基质混合处理等(Berova & Zlatev,2000;黄少华 等,2006;张静 等,2007;刘东冉 等,2008),其主要通过抑制内源生长素(IAA)和赤霉素(GA)的合成,促进IAA和GA的降解,抑制幼苗徒长。

5.3 机械调节

机械刺激对幼苗生长具有重要调控作用,可降低部分蔬菜作物茎及叶柄的伸长,从而抑制幼苗徒长。目前常用的机械刺激包括:接触刺激(brushing)、阻抑或阻压(impedance)及振荡处理等。

接触刺激是一种有效的机械调节方式,少量刺激便可有效抑制幼苗徒长,频率过高可诱发机械伤害。前人研究表明,接触刺激可有效降低番茄、黄瓜等蔬菜幼苗的植株高度,一天中的处理时间和频率对株高没有显著影响,但处理天数与之显著相关,连续的接触刺激处理可使番茄幼苗株高降低20%(Latimer,1991;Garner & Bjorkman,1996)。

阻抑或阻压主要是通过丙烯醇薄片、聚酯薄膜、纤维玻璃等材料阻压幼苗顶部,防止幼苗徒长,但这种处理方式会导致幼苗茎弯曲,不利于机械化移栽(Piszczek & Jerzy,1987)。

振荡处理可有效控制番茄幼苗的生长,每天连续多次振荡处理较连续振荡处理效果更好,植株高度降低更多,但整体的处理效果不如接触刺激(Latimer & Mitchell,1988)。

6 展望

幼苗徒长是蔬菜集约化育苗过程中的常见问题,目前防控上主要依赖植物生长调节剂,但在育苗过程中生长调节剂用量不容易把控,浓度过高易产生药害,浓度过低则达不到防控效果,亟需研究与开发新的徒长防控技术及实用产品。为此,今后研究应着重分析不同环境信号对幼苗徒长的交互作用;深入了解细胞膨大与分裂调控机制及其在下胚轴伸长过程中的作用;利用转录组学、蛋白质组学及代谢组学相结合的方法,探明环境因子调控下胚轴伸长的信号通路,分析不同环境信号的交叉调控位点及其生物学功能,这将是全面揭示幼苗徒长机制及广谱防控技术开发的关键。

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Research Progress on Morphological and Physiological Characteristics of Vegetable Leggy Seedlings

WANG Hong-fei,SHANG Qing-mao*
(Key Laboratory of Biology and Genetic Improvement of Horticultural Crops,Institute of Vegetables and Flowers,Chinese Academy of Agricultural Sciences,Collaborative Innovation Center of Protected Vegetable Surround Bohai Gulf Region,Beijing 100081,China)

Intensive vegetable seedlings culture usually took with porous conjoined plug as container,which had high density,less space for root system development and weak buffer capacity of rhizosphere. It was very easy for seedlings to over grown. The morphological and physiological metabolism of leggy seedlings were different from the normal ones,including elongated hypocotyl and internode,enlarged leaf angle,reduced leaf thickness and root to shoot ratio,increased moisture content in tissue,weakened adaptability to biotic and abiotic stress. This review summarized the morphological characteristics of vegetable leggy seedlings,flowering habit,resistance expression,physiological metabolism and related preventing techniques,etc.,aiming at providing reference for preventing leggy seedlings and developing related technology.

Leggy seedling;Morphological characteristic;Flowering habit;Physiological metabolism;Environmental factor

王红飞,女,博士研究生,专业方向:蔬菜种苗发育调控与繁育技术,E-mail:wanghongfei0329@163.com

*通讯作者(Corresponding author),尚庆茂,男,研究员,博士生导师,专业方向:蔬菜栽培生理及分子生物学,E-mail:shangqingmao@ caas.cn

2017-03-21;接受日期:2017-05-26

国家自然科学基金项目(31172001),国家现代农业产业技术体系建设专项(CARS-25),公益性行业(农业)科研专项(201303014),中国农业科学院科技创新工程项目(CAAS-ASTIPIVFCAAS)

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