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硅 增强 高粱抗 干 旱 、 盐 和 镉 胁迫能力以及缓解 钾 缺乏 的作 用机制
刘朋
Subtype博士
Thesis Advisor邓西平
2014-05
Degree Grantor中国科学院研究生院
Place of Conferral北京
Keyword 干旱 盐胁迫 镉毒害 水通道蛋白 根系水导 有机酸
Abstract

硅是组成地壳的重要元素之一,其含量在所有元素中占第二位,仅次于氧。
尽管硅是否能被认定为一种植物生长的必需元素还存着很大的争议,但是外源施
加硅改善植物对逆境胁迫的抗性已经被广泛的报道。并且对硅改善植物抗逆性的
作用机制进行了大量的研究。过去大量的研究的结果表明:硅沉积在植物组织上
所形成的物理障碍(Physical barrier)是硅增强植物抗生物胁迫和非生物胁迫的
主要作用机理。但是随着对其作用机制进行深入的探讨,越来越多的证据表明外
源施加硅也可以在分子和生理水平上调控植物的生长增强植物的抗逆性。本论文
的主要研究目的是以高粱为研究对象探讨外源施加硅对高粱抗旱,抗盐,镉毒害
以及钾亏缺的影响及作用机制。
1: 硅提高高粱抗旱性 的影响 及其作用机制 硅改善植物抗旱性已经进行了
大量研究,但是其作用机制还不明确,尤其是硅能否可以提高植物的吸水能力还
是空白。本实验通过在水培和沙培的条件下,研究外源施加硅在干旱胁迫下对高
粱幼苗水分吸收及运输的影响。干旱胁迫导致幼苗干重,光合速率,蒸腾速率,
气孔导度以及水分状况下降。外源施加硅可以显著地缓解干旱对上述指标的负效
应。外源施加硅对幼苗茎水分运输效率(L sc )没有显著影响,但是在干旱条件
下经过硅处理幼苗的整株水导(K plant )和根水导(Lp)却明显高于不加硅幼苗。
并且在干旱胁迫下硅提高整株蒸腾速率幅度和提高整株水导以及根水导的幅度
变化基本一致。我们通过外源施加水通道蛋白抑制剂 HgCl 2 来验证硅改善高粱的
水导是否与水通道蛋白有关。结果表明:在水分胁迫的条件下,经过 HgCl 2 处理
后幼苗的蒸腾速率迅速下降,并且加硅与不加硅的处理之间蒸腾的差异消失。然
后经过 DTT 恢复后。外源施加硅的幼苗的蒸腾速率显著高于未经过硅处理的幼
苗。除此之外,在水分胁迫的条件下,外源施加硅可以上调水通道蛋白的表达水
平。我们的研究结果表明:在水分胁迫下,硅上调水通道蛋白表达,改善根系水
导,增强根系的吸水,从而维持植物较高的蒸腾和光合速率来增强高粱抗旱能力。2: 硅提高高粱抗盐性 的影响 及其作用机制 施硅改善植物抗盐能力已经在
多种植物上得到了确证,但是关于硅提高植物抗盐的机理研究过去主要集中在外
源施加硅减少植物对钠离子的吸收,从而缓解了盐引起的离子毒害。而关于硅是
否能通过改善高盐引起的渗透胁迫来提高植物抗盐能力一直被忽视。在本实验
中,我们利用高粱为材料,以水培的方式研究硅对缓解盐引起的渗透胁迫的作用
及其机制。结果表明:在正常条件下,外援施加硅对高粱幼苗的生长没有显著影
响。当幼苗遭受到短时间的盐胁迫后,光合速率,蒸腾速率显著下降,但是外源
施加硅可以缓解这种下降趋势。同时加硅处理的幼苗,其叶片水分状况及叶片伸
长速率仍然保持在一个相对较高的水平。短时间的盐胁迫(2 小时),高粱幼苗
的根系水导显著下降,而外源施加硅可以缓解根系水导的下降。在盐胁迫条件下,
外源添加 HgCl 2 降低高粱的蒸腾速率,同时在加硅与不加硅高粱间的蒸腾速率差
异被消除,导致加硅与不加硅幼苗的蒸腾速率下降到同一水平。经过-巯基乙醇
恢复后,加硅处理的幼苗的蒸腾速率仍然高于未加硅处理的幼苗的蒸腾速率。这
个结果表明:硅通过调节水通道蛋白的活性来缓解盐导致的水导的下降。进一步
研究发现,在盐胁迫的条件下,外源施加硅能增强几种水通道蛋白(PIP)基因
的表达水平。同时,外源施加硅可以通过增强抗氧化酶的活性阻止根系 H 2 O 2 的
积累。我们还发现预先经过过氧化氢酶(CAT)处理的幼苗的蒸腾速率与经过硅
处理的幼苗的蒸腾速率相似。说明硅抑制 H 2 O 2 的积累也有可能有利于增强水通
道蛋白活性。本研究结果表明:在短时间盐胁迫条件下,外源施加硅可以通过上
调水通道蛋白的表达水平及缓解由于 H 2 O 2 的积累而导致的水通道蛋白活性的下
降来调节水通道蛋白的活性,从而提高根系水导,促进根系吸水,进而增强对高
盐所引起的渗透胁迫的抗性。
3: 硅提高高粱抗镉毒性 的影响 及其作用机制 硅增强植物的抗镉毒害已经
被广泛的报道,但是其作用机理并不十分明确。本实验利用高粱幼苗在水培的条
件下,研究在镉毒害的条件下,外源施加硅对高粱的生长及抗氧化酶活性,有机
酸含量的影响。结果表明:外源施加硅能显著地缓解镉毒害,表现为在镉胁迫下,
高粱无论地上部分还是地下部分鲜重及干重都高于不加硅的处理。抗氧化酶结果
表明:在正常条件下,外源施加硅对三种抗氧化酶的活性没有显著的影响。但是
在镉毒害的条件下,除 SOD 外,CAT 和 POD 的活性显著增强。与此相对应的是 MDA 的含量在镉胁迫下明显增加,硅显著地降低 MDA 的含量。对有机酸的
分析发现:叶片和根在镉毒害和硅处理下,有机酸的种类,含量及变化趋势不尽
相同。在镉毒害的条件下,叶片中有 3 种有机酸能够检测到:草酸,丙二酸,丁
二酸,并且其含量都在外源施加硅的条件下增加。而在根系中所检测到的 4 种有
机酸中,草酸和丙二酸的含量受到硅的调节而增加,柠檬酸的含量不受影响,而
苹果酸的含量却有下降的趋势。上述结果表明:外源施加硅增强高粱幼苗的抗镉
胁迫与其增强高粱抗氧化酶活性及增加高粱体内有机酸的含量相关。
4: 硅提高高粱抗缺钾能力 的影响 及其作用机制 硅改善植物抗缺钾能力虽
然也有报道,但是其机制也不明确。本实验采用水培方式研究硅对高粱幼苗缺钾
的影响及作用机制。研究结果表明:无论是地上部分,地下部分干重和鲜重在低
钾条件下都会出现显著下降。但是外源施加硅能有效地缓解这种下降的趋势。在
此基础上,我们对老叶和新叶的光合速率,蒸腾速率及气孔导度进行研究。结果
表明:低钾胁迫降低了无论是老叶还是新叶的光合速率。但是值得注意的是:外
源施加硅后,老叶的光合速率下降趋势得到缓解。造成这一现象的主要原因可能
是在缺钾的条件下,外源施加硅能维持老叶的气孔导度,蒸腾速率处在一个相对
较高的水平。外源施加硅对新叶中上述的参数的变化没有显著的影响。
本实验分别研究了外源施加硅增强高粱幼苗抗旱、盐、镉及缓解钾缺乏的影
响及作用机制。实验结果表明:除了“物理障碍”以外,硅调控植物增强对逆境
抗性的作用机制不完全相同。换句话说:当植物遭受到不同的外界环境胁迫时,
硅通过调控不同的分子和生理功能增强植物的抗逆性。结合过去的研究进展,我
们认为:造成这一现象的原因可能是硅可以作为一种“调节器”通过感受到不同的
外界刺激,调节下游的相关基因的表达从而调控植物的生理活动的变化,适应外
界环境胁迫。
关键词:硅,干旱,盐胁迫,镉毒害,水通道蛋白,根系水导,有机酸

Other Abstract

Silicon is the second most abundant element in the soil after oxygen. Although
silicon is not currently considered an essential element for higher plants, silicon
uptake has frequently been found to be beneficial in increasing plant resistance to
multiple stresses. Moreover, previous experiments were conducted to investigate the
mechanism of silicon on enhancing plant resistance to stress. There are accumulating
evidence demonstrated that the physical barrier formed by silicon deposited the
organism was responsible for silicon enhancing plant resistance to stress. However,
with the further extended investigation, the molecular and physiological mechanism
was also involved in silicon-induce resistance to stress. The objective of this paper
was to investigated the the effect and mechanism of silicon on enhancing the
resistance to water deficient, salt, cadmium and K-deficiency stress.
1: The influence and mechanism of silicon on enhancing sorghum seedlings
resistance to drought. The fact that silicon application alleviates water deficit
stress has been widely reported, but the underlying mechanism remains unclear. Here
we investigated the effects of silicon on water uptake and transport of sorghum
seedlings (Sorghum bicolor L.) growing under water deficit stress in both hydroponic
and sand culture. Water deficit dramatically decreased dry weight, photosynthetic rate,
transpiration rate, stomatal conductance and leaf water content, but silicon application
reduced these stress-induced decreases. Meanwhile, although silicon application had
no effect on stem water transport capacity, but whole plant hydraulic conductance
(K plant ) and root hydraulic conductance (Lp) were higher in silicon-treated seedlings
than those without silicon under water deficit stress. Furthermore, the changes in
transpiration rate were consistent with the changes in K plant  and Lp. The contribution
of aquaporin to Lp was characterized using the aquaporin inhibitor mercury. Under
water deficit stress, the exogenous application of HgCl 2 decreased the transpiration  rates of seedlings with and without silicon to the same level; after recovery induced
by dithiothreitol (DTT), however, the transpiration rate was higher in silicon-treated
seedlings than in untreated seedlings. In addition, transcription levels of several root
aquaporin genes were increased by silicon application under water deficit stress.
These results indicate that the silicon-induced up-regulation of aquaporin, which was
supposed to increase Lp, was involved in increasing root water uptake under water
deficit stress.
2: The influence and mechanism of silicon on enhancing sorghum seedlings
resistance to salt. Silicon improved plant salt resistance has been widely reported.
Most previous researches were focused on how silicon prevents Na + uptake and
accumulation, but the performance and underlying mechanism of silicon on
alleviating salt-induced osmotic stress has been largely ignored. In the present study,
the mechanism of silicon on alleviating salt-induced osmotic stress was investigated
by sorghum in a hydroponic system. Silicon had no effect on seedlings growth under
normal condition. Under salt stress, photosynthesis and transpiration rate were
decreased, but their decrease were alleviated by silicon application. Meanwhile, leaf
water content and leaf elongation rate were kept at a higher level than that without
silicon. Root hydraulic conductance (Lp) of seedlings were inhibited by salt, but
silicon application alleviated the inhibition. Under salt stress, the transpiration rates of
seedlings both with and without silicon were decreased to the same level by HgCl 2
treatment, and partially recovered by -Mercaptoethanol treatment, suggesting that
aquaporin was responsible for the alleviation the decrease in Lp. Moreover, parts of
aquaporin genes transcription levels were up-regulated by silicon. Under salt stress,
silicon inhibits the increase in root H 2 O 2  contents and enhanced antioxidant enzyme
activities. Meanwhile, similar as silicon, pre-treatment by catalase resulted in
alleviation decreased in transpiration rate, indicating that silicon mediated H 2 O 2
accumulation was benefit to enhance aquaporin activity. These results indicate that
under short-term salt stress, silicon application could alleviate the decrease of Lp by
mediating aquaporin activity, which lead to increase the water uptake and resist to  salt-induced osmotic stress.
3: The influence and mechanism of silicon on enhancing sorghum seedlings
resistance to cadmium. Although the effect of silicon on cadmium tolerance is
wildly reported, the underlying mechanism is still unclear. In the present study, we
investigated the effect of silicon on sorghum seedling growth, anti-oxidant enzyme
activity and organic acids content. The result indicated silicon application alleviated
cadmium-induced the decrease in fresh weight and dry weight both in shoot and root.
The results of anti-oxidant enzyme activity indicated that under control condition, the
anti-oxidant enzyme activity was not affected by silicon. However under cadmium
stress, the CAT and POD activity were significantly increased by silicon. The SOD
activity was not influenced by silicon. Corresponding to these results, under cadmium
stress, MDA was increased, while it was decreased by silicon. The results of organic
acid (OA) indicated that the species, content and tendency of OA were different in
leaf and root. In leaf, 3 types OA were detected including Oxalic acid; Propanedioic
acid; Succinic acid. All of them were increased by silicon under cadmium stress. In
the shoot, there are 4 types OA were detected: Oxalic acid; Malic acid; Propanedioic
acid; Citric Acid. Oxalic acid and Propanedioic acid content were increased by silicon.
Citric Acid content was not influenced by silicon. However, the Malic acid was
decrease by silicon. All the results indicated that: the enhancement of anti-oxidant
enzyme activity and OA content were involved in the silicon-induced the sorghum
seedlings cadmium tolerance.
4: The influence and mechanism of silicon on enhancing sorghum seedlings
resistance to K-deficiency. It has been reported that silicon application could
alleviate K-deficiency stress, but the mechanism was unclear. In the present study, we
investigated the mechanism of silicon on alleviating K-deficiency in hydroponic
culture. K-deficiency significantly decreased the fresh and dry weight of both shoot
and root. However silicon application alleviated the decrease in biomass. Based on
this result, we investigated the old and new leaf’s photosynthetic rates respectively.
The results indicated that K-deficiency decreased the photosynthetic rate no matter in   both old and new leaf. It is worth noting that silicon application significantly
alleviated the decrease in old leaf’s photosynthetic rate. Which is mainly due to
silicon application could maintain the stomatal conductance and transpiration rate at a
relative high level compared with that without silicon application under K-deficiency
condition.
The influence and mechanism of silicon on enhancing sorghum seedlings
resistance to drought, salt, cadmium and K-deficiency were investigated in our
experiment. Summarized the results, we find that the mechanisms of silicon on
enhancing plant resistance to different stresses were not the same except the physical
barrier. That is to say, under different stress conditions silicon could regulated the
different function of molecular and physiology to enhance resistance to the stresses.
Combined with the previous result, we speculated that silicon act as the “modulator”
which could sense the stress firstly and then regulated relevant genes expression to
enhance resistance to environmental stress.
KEY WORDS: silicon, drought, salt, cadmium, aquaporin, root hydraulic
conductance, organic acid

Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/9014
Collection水保所知识产出(1956---)
Recommended Citation
GB/T 7714
刘朋. 硅 增强 高粱抗 干 旱 、 盐 和 镉 胁迫能力以及缓解 钾 缺乏 的作 用机制[D]. 北京. 中国科学院研究生院,2014.
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