【摘要】：鎘(Cd)對(duì)于動(dòng)物和植物組織來說是一種有毒的和非必需的重金屬。對(duì)植物在應(yīng)對(duì)重金屬傷害及植物對(duì)重金屬的抗性機(jī)理的探索與研究是非常重要的課題,只有徹底了解植物在應(yīng)對(duì)重金屬脅迫傷害及其對(duì)重金屬的抗性機(jī)理,才可能提出可以讓植物避免遭受重金屬傷害的有效的措施和提高植物抗重金屬能力的重要方法,這樣才有益于治理土壤中的重金屬污染,保護(hù)地球生態(tài)環(huán)境和生產(chǎn)綠色健康的食品。外源一氧化氮(NO)是一種信號(hào)分子,對(duì)調(diào)節(jié)非生物和生物脅迫下各種生理反應(yīng)具有重要作用。導(dǎo)致這些生理反應(yīng)的重金屬脅迫的信號(hào)在植物體內(nèi)如何傳遞,NO在其中起什么作用,怎樣調(diào)動(dòng)防御系統(tǒng)并最終影響植物生長發(fā)育、生理代謝和基因表達(dá)等過程的,如何通過人為調(diào)控植物對(duì)重金屬的耐受機(jī)制整體過程中的一些過程,來提高植物對(duì)重金屬的耐性,增加或減少對(duì)重金屬的吸收,并應(yīng)用于重金屬污染區(qū)的植物修復(fù)和農(nóng)業(yè)生產(chǎn)?目前未見研究報(bào)道。紫花苜蓿(Medicago sativa L.)作為多年生的一種草本植物以其豆科紫花苜蓿屬獨(dú)有的特點(diǎn)在牧草業(yè)被認(rèn)為是牧草之最。廣泛分布在世界溫帶地區(qū),27℃的溫度最適于幼苗生長。其廣泛的根系使其具有耐旱性,可以增強(qiáng)降解細(xì)菌的活性,促進(jìn)多氯聯(lián)苯(PCBs),多環(huán)芳烴(PAH)和三硝基甲苯(TNT)等幾種有機(jī)污染物的生物降解率,尤其是在含有較低含量有機(jī)質(zhì)的土壤中。紫花苜蓿含有豐富的維生素A、C、E、K及礦物質(zhì)和微量元素,生長快速,根系發(fā)達(dá)、壽命長以及抗性好等特性,是有毒金屬植物修復(fù)的有前景的植物。已有研究表明,紫花苜蓿對(duì)重金屬的抗性比較強(qiáng)并且具有很好的吸收富集能力,其中對(duì)Cd的吸收系數(shù)最大,已有研究證明紫花苜蓿對(duì)Cd污染土壤的修復(fù)能力最好,被認(rèn)為是重金屬污染植物修復(fù)的環(huán)保技術(shù)之一。為探討硝普鈉(SNP,外源NO供體)對(duì)Cd在紫花苜蓿幼苗萌發(fā)過程中的毒性影響及其在植物修復(fù)Cd污染土壤的應(yīng)用,本研究測定了氧化應(yīng)激水平、抗氧化酶活性、水解酶活性、貯藏物質(zhì)含量、鮮重、干重量和Cd的吸收等參數(shù),分析了外源NO對(duì)Cd脅迫下紫花苜蓿種子萌發(fā)及生長的影響。萌發(fā)和生長實(shí)驗(yàn)進(jìn)行5天,每隔24小時(shí)記錄并測定一次各個(gè)指標(biāo)。為揭示外源NO可以顯著緩解Cd脅迫下紫花苜蓿萌發(fā)期間Cd毒性提供了證據(jù)。用不同濃度的CdCl_2對(duì)種子和幼苗進(jìn)行預(yù)處理,結(jié)果表明CdCl_2對(duì)紫花苜蓿種子的發(fā)芽和幼苗生長的毒性作用隨著其濃度的增加而增加。30μM的CdCl_2對(duì)紫花苜蓿的幼苗生長有明顯的抑制作用而不會(huì)對(duì)其發(fā)芽率造成明顯的影響。高濃度的CdCl_2會(huì)導(dǎo)致發(fā)芽率嚴(yán)重下降,從而減少了每組實(shí)驗(yàn)中所產(chǎn)生幼苗的可用樣本。因此本研究采用30μM CdCl_2模擬Cd脅迫。在30μM CdCl_2模擬的Cd脅迫下,以25、50、100、200、300、400和500μM SNP分別處理紫花苜蓿種子5天,每隔24小時(shí)記錄并測定一次以下指標(biāo):發(fā)芽率、發(fā)芽指數(shù)、壯苗指數(shù)、根長和芽長作為萌發(fā)參數(shù);脯氨酸(Pro)水平,相對(duì)電導(dǎo)率(REC),脂質(zhì)過氧化(MDA)和活性氧(ROS)如H2O2和O2-產(chǎn)生速率作為Cd作用下的氧化應(yīng)激反應(yīng)參數(shù);超氧化物歧化酶(SOD)、過氧化物酶(POD)、抗壞血酸過氧化物酶(APX)、過氧化氫酶(CAT)和谷胱甘肽還原酶(GR)等抗氧化酶活性作為抗氧化機(jī)制的參數(shù);α-淀粉酶和β-淀粉酶活性作為水解酶的參數(shù);可溶性蛋白、可溶性淀粉、可溶性糖和還原性糖作為儲(chǔ)存物質(zhì)的參數(shù)。1、外源NO能夠緩解Cd脅迫對(duì)紫花苜蓿種子萌發(fā)和幼苗生長的抑制作用。30μM Cd脅迫加速了儲(chǔ)存物質(zhì)的分解,顯著降低了種子發(fā)芽指數(shù)和幼苗活力指數(shù),抑制了幼苗生長,外源施用的不同濃度的SNP表現(xiàn)出顯著的緩解重金屬脅迫的作用,具有緩解脅迫和促進(jìn)植物生長的能力。在最佳濃度下,緩解作用呈顯著的線性增加,而超過最佳濃度時(shí)則使植物生長受抑制。這種反應(yīng)更可能是通過有效的外源NO激活植物防御或耐受機(jī)制的結(jié)果。這證實(shí)了以前關(guān)于砷脅迫下的種子發(fā)芽過程中的NO的保護(hù)作用的研究。對(duì)Cd脅迫條件下水稻種子萌發(fā)及其幼苗生長的研究已經(jīng)闡明了外源NO對(duì)Cd毒性的重要性,SNP能夠顯著提高發(fā)芽率,發(fā)芽指數(shù)和幼苗活力指數(shù),在芝麻苗中也已經(jīng)報(bào)道了類似的結(jié)果。在本研究中,外源性NO成功緩解Cd損傷,可能也以與其他生物或非生物脅迫類似的方式運(yùn)行。然而,在SNP的最佳濃度之上,植物或幼苗表現(xiàn)出相同的防御機(jī)制,這類似于多年生黑麥草對(duì)Cd脅迫的防御機(jī)制。200μM SNP能有效緩解30μM的Cd對(duì)紫花苜蓿種子萌發(fā)和有生長的抑制作用。2、外源NO通過激活抗氧化系統(tǒng),清除活性氧,緩解Cd脅迫下紫花苜蓿的氧化損傷。Cd能夠誘導(dǎo)幼苗中產(chǎn)生ROS,如O2-和H2O2,它們導(dǎo)致膜脂過氧化,電解質(zhì)滲漏和氧化應(yīng)激。本研究中,通過測定REC和MDA,H2O2和O2-來研究膜滲漏,以闡明由于氧化應(yīng)激引起的植物損傷。實(shí)驗(yàn)結(jié)果表明,隨時(shí)間延長,Cd誘導(dǎo)這些分子的過度積累導(dǎo)致紫花苜蓿種子中的氧化損傷并抑制幼苗生長。生理變化等多種機(jī)制都與植物阻止或減輕非生物或非生物脅迫有關(guān)。應(yīng)對(duì)環(huán)境脅迫,許多植物物中的Pro會(huì)積累,Ahmad曾報(bào)道了NO在非生物脅迫下Pro的代謝中的調(diào)節(jié)作用。在本研究中,暴露于Cd脅迫的幼苗Pro水平高于對(duì)照幼苗,應(yīng)用SNP后,其水平進(jìn)一步下降,特別是當(dāng)SNP濃度高于200μM時(shí),但長期暴露于200μM以上濃度的SNP時(shí)呈現(xiàn)Pro含量增加的趨勢,這進(jìn)一步證實(shí)了已有報(bào)道的類似的研究結(jié)果。為了應(yīng)對(duì)和中和ROS的毒性,植物發(fā)展的內(nèi)源性抗氧化酶系統(tǒng)包括CAT,POD,SOD,APX,GR等抗氧化酶。SOD通過促進(jìn)超氧化物自由基轉(zhuǎn)化來保護(hù)細(xì)胞免受氧化應(yīng)激的最有效的酶被極大地抑制,其活性顯著低于對(duì)照(CK),可能是由于Zn2+-SOD復(fù)合物的氫鍵弱,固體含量低,Cd2+可以很容易地替代SOD活性位點(diǎn)的Zn2+,使SOD活性降低。在本研究中,Cd的積累導(dǎo)致H2O2和O2-的顯著產(chǎn)生,SOD活性降低,而采用外源性NO處理則使SOD活性水平提高,特別是在處理的前3天,處理后期,隨SNP濃度的增加,SOD酶活性雖然有所降低但仍然高于或與Cd單獨(dú)處理持平,證實(shí)了早期關(guān)于水稻和番茄幼苗研究中類似的報(bào)道。外源SNP處理使POD活性水平在整個(gè)萌發(fā)過程中均高于Cd單獨(dú)處理,表明POD在萌發(fā)過程中都保持較高活性以清除H2O2。APX僅在萌發(fā)前2天當(dāng)SNP濃度低于200μM時(shí)活性增強(qiáng),SNP濃度大于200μM時(shí)活性減弱,在萌發(fā)后期(3-5天)SNP處理使APX活性顯著低于Cd單獨(dú)處理,且隨SNP濃度的增加無顯著性變化,表明APX僅在紫花苜蓿種子萌發(fā)初期具有清除ROS的作用。CAT與APX類似,在萌發(fā)前4天具有清除ROS的作用。Cd脅迫使GR活性從萌發(fā)第2天起就顯著低于CK,而SNP處理僅在萌發(fā)第1天和第3天使GR活性有所升高,但隨SNP濃度的增加并沒有顯示出規(guī)律性的變化,表明NO和GR活性誘導(dǎo)之間的關(guān)系較為復(fù)雜,有待進(jìn)一步研究。3、外源NO能夠增加Cd脅迫下紫花苜蓿幼苗貯藏儲(chǔ)備物質(zhì)的含量,增強(qiáng)相關(guān)酶活性。發(fā)芽過程的特征是通過儲(chǔ)存物質(zhì),如碳水化合物和蛋白質(zhì)等通過水解酶水解新形成的物質(zhì)用于形成新的結(jié)構(gòu)。儲(chǔ)存物質(zhì)被水解酶水解為呼吸作用和各種合成代謝反應(yīng)提供能量,以形成代謝產(chǎn)物。負(fù)責(zé)這些儲(chǔ)備物質(zhì)如淀粉分解的酶是α-淀粉酶和β-淀粉酶,已有報(bào)道,Cd脅迫會(huì)導(dǎo)致儲(chǔ)備物質(zhì)的動(dòng)員受到限制。隨萌發(fā)時(shí)間的延長和SNP濃度的增加,SNP激活α-淀粉酶和β-淀粉酶,調(diào)節(jié)Cd脅迫條件下紫花苜蓿種子中可溶性蛋白、還原糖和可溶性糖含量。30μMCd脅迫使紫花苜蓿種子α和β-淀粉酶活性顯著降低,可溶性蛋白和淀粉含量也在處理的第2天顯著下降,這是抑制種子萌發(fā)的主要因子。本研究表明,外源SNP對(duì)30μMCd脅迫下紫花苜蓿幼苗的萌發(fā)有很強(qiáng)的刺激作用,使淀粉酶、可溶性蛋白和淀粉含量顯著高于僅用Cd處理的幼苗,這一研究結(jié)果與外源性NO對(duì)Cd脅迫下發(fā)芽的豌豆種子淀粉酶活性影響的研究結(jié)果一致。通過在Cd處理的幼苗中施用外源NO,α-淀粉酶和β-淀粉酶的活性均顯著增強(qiáng);在處理第2天,可溶性淀粉和蛋白質(zhì)的含量均高于僅用Cd處理的幼苗中的含量,這有利于改善紫花苜蓿幼苗的萌發(fā)。實(shí)驗(yàn)的前三天,SNP濃度低于100μM時(shí),能調(diào)節(jié)可溶性糖的含量,當(dāng)濃度超過100μM有相反的影響。除了SNP濃度在25和100μM時(shí)幼苗還原糖含量比較高,其他處理下幼苗體內(nèi)還原糖含量均無顯著差異,并且還原糖的產(chǎn)生量幾乎是恒定的。4、外源NO顯著降低紫花苜蓿種子中Cd的積累并增加種子鮮重和干重。Cd作為非必需和有害元素之一,可以通過與Ca2+和K+等植物中的其他微量和大量營養(yǎng)物質(zhì)競爭來干擾植物體內(nèi)平衡,甚至也可以通過水來運(yùn)輸。發(fā)生這種情況與鮮重和干重物質(zhì)的減少有關(guān),已有研究報(bào)道,水含量受植物中Cd濃度的高度影響。本研究中,只要種子暴露于Cd脅迫下,與CK種子相比,種子的干重和鮮重也隨著暴露時(shí)間的延長而受到顯著的影響。在向日葵和高粱種子中也有類似的研究結(jié)果。據(jù)報(bào)道外源性NO阻礙重金屬進(jìn)入植物細(xì)胞壁,或調(diào)節(jié)植物細(xì)胞壁內(nèi)多余Cd的細(xì)胞分布和積累。本研究實(shí)驗(yàn)結(jié)果與水稻幼苗研究中,水稻葉中汞的吸收和水稻幼苗對(duì)銅的攝取的研究結(jié)果類似。這表明SNP可能是保護(hù)種子免受重金屬毒性的合適的化合物之一。30μM的Cd沒有顯著降低萌發(fā)率,但萌發(fā)指數(shù),SVI,根長和莖長受Cd毒性影響很大;發(fā)現(xiàn)30μM CdCl_2誘導(dǎo)Pro水平升高,REC,MDA以及ROS過度產(chǎn)生,Cd通過誘導(dǎo)抗氧化酶活性降低的能力對(duì)紫花苜蓿種子的防御機(jī)制有重大的阻礙作用;α-淀粉酶,β-淀粉酶的活性受Cd毒性的顯著影響,導(dǎo)致儲(chǔ)存物質(zhì)可溶性蛋白質(zhì)、可溶性淀粉、可溶性糖和還原糖的損害;Cd也顯著影響種子鮮重和干重。外源NO顯示能逆轉(zhuǎn)Cd對(duì)萌發(fā)率、下胚軸長度、根長、發(fā)芽指數(shù)和幼苗活力指數(shù)的負(fù)面影響,發(fā)現(xiàn)200μM SNP對(duì)30μM Cd毒性的緩解作用最有效。外源NO在抵抗ROS過度生成引起的氧化損傷方面是有效的,因?yàn)樗梢越档桶l(fā)芽紫花苜蓿幼苗的MDA、REC和ROS水平。外源NO也被揭示為能夠增強(qiáng)抗氧化系統(tǒng)。外源NO通過調(diào)節(jié)α和β-淀粉酶的活化調(diào)節(jié)可溶性淀粉、還原糖和可溶性糖的動(dòng)員,在抵消Cd毒性引起的貯藏物質(zhì)的損害方面起主要作用。外源性NO對(duì)植物的Cd吸收產(chǎn)生抑制作用,增加干重和鮮重。一般來說,加入200μM的SNP顯示為減輕30μM Cd毒性最顯著。紫花苜蓿在修復(fù)重金屬如Cd、Cu、Pb等污染土壤方面的能力非常突出,而在中國特別是西北地區(qū)有大面積種植紫花苜蓿作為畜牧業(yè)發(fā)展的基礎(chǔ),由此可見其在應(yīng)對(duì)逆境環(huán)境下的發(fā)展前景很廣闊。光合作用是植物新陳代謝以生長的基本生理活動(dòng),對(duì)于NO在Cd脅迫下對(duì)紫花苜蓿凈光合速率、蒸騰速率、氣孔導(dǎo)度、胞間CO2濃度、葉綠素?zé)晒鈪?shù)以及葉黃素循環(huán)是怎樣影響的還有待探討,這是下一步研究的方向和目標(biāo)。建議進(jìn)一步采用遺傳和蛋白質(zhì)組學(xué)分析及其他生理學(xué)方法,以了解外源NO在植物代謝功能中的細(xì)節(jié),這將有助于進(jìn)一步了解這種多面體化合物,用于植物緩解不同種類生物和非生物脅迫,使紫花苜蓿能夠更好的應(yīng)用于重金屬污染土壤的植物修復(fù)中。
[Abstract]:Cadmium (Cd) is a toxic and non-essential heavy metal for animal and plant tissues. It is very important to explore and study the mechanism of plant resistance to heavy metals and heavy metals in response to heavy metal injuries. Only thoroughly understand the mechanism of plant resistance to heavy metals can we possibly put forward. Effective measures to prevent plants from being harmed by heavy metals and important ways to improve their resistance to heavy metals are beneficial to the control of heavy metal pollution in the soil, the protection of the earth's ecological environment and the production of green and healthy food. Exogenous nitric oxide (NO) is a signaling molecule that regulates abiotic and biological stresses. Species play an important role in physiological responses. How these physiological responses are caused by heavy metal stress signals are transmitted in plants, what role NO plays in them, how to mobilize defense systems and ultimately affect plant growth and development, physiological metabolism and gene expression, and how to regulate plant tolerance to heavy metals through human regulation Some processes in the body process to improve plant tolerance to heavy metals, increase or decrease the uptake of heavy metals, and apply to phytoremediation and agricultural production in heavy metal contaminated areas have not been reported. It is widely distributed in temperate regions of the world and is most suitable for seedling growth. Its extensive roots make it drought-resistant, enhance the activity of degrading bacteria, and promote the biodegradability of several organic pollutants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAH) and trinitrotoluene (TNT), especially Alfalfa is a promising plant for phytoremediation of toxic metals because of its rich vitamin A, C, E, K, minerals and trace elements, rapid growth, well-developed roots, long life span and good resistance. Alfalfa is considered as one of the environmental protection technologies for phytoremediation of heavy metal contaminated soils. In order to study the toxic effects of sodium nitroprusside (SNP, exogenous NO donor) on cadmium during the germination of Alfalfa seedlings, alfalfa has the greatest absorption and enrichment capacity. The effects of exogenous NO on the germination and growth of Alfalfa Seeds under Cd stress were analyzed. The experiment was carried out for 5 days, every 24 hours and recorded and measured. The results showed that the toxicity of CdCl_2 to alfalfa seed germination and seedling growth increased with the increase of CdCl_2 concentration. The growth of alfalfa seedlings was obviously inhibited but not significantly affected by CdCl_2. High concentration of CdCl_2 could lead to a serious decrease in germination rate, thus reducing the available samples of seedlings produced in each group of experiments. Alfalfa seeds were treated with 100,200,300,400 and 500 mu M SNP for 5 days, and the following indices were recorded and measured every 24 hours: germination rate, germination index, seedling vigor index, root length and bud length as germination parameters; proline (Pro) level, relative conductivity (REC), lipid peroxidation (MDA) and reactive oxygen species (ROS), such as H2O2 and O2 - production rate as Cd production. Oxidative stress reaction parameters; superoxide dismutase (SOD), peroxidase (POD), ascorbic acid peroxidase (APX), catalase (CAT), glutathione reductase (GR) and other antioxidant enzymes as antioxidant mechanism parameters; alpha-amylase and beta-amylase as hydrolytic enzyme parameters; soluble protein, soluble protein, soluble amylase; Starch, soluble sugar and reducing sugar were used as storage material parameters. 1. Exogenous NO could alleviate the inhibition of Cd stress on Seed Germination and seedling growth of alfalfa. SNP showed a significant role in alleviating heavy metal stress and promoting plant growth. At the optimum concentration, the alleviation increased linearly, while above the optimum concentration, plant growth was inhibited. This response was more likely to be the result of effective exogenous NO activating plant defense or tolerance mechanisms. Fruit. This confirms previous studies on the protection of nitric oxide during seed germination under arsenic stress. Studies on Rice Seed Germination and seedling growth under cadmium stress have clarified the importance of exogenous nitric oxide to cadmium toxicity. SNP can significantly improve germination rate, germination index and seedling vigor index, and has been reported in sesame seedlings. In this study, exogenous nitric oxide successfully alleviated Cd damage and probably operated in a similar manner to other biotic or abiotic stresses. However, above the optimal concentration of SNP, plants or seedlings exhibited the same defense mechanism similar to that of perennial ryegrass under Cd stress. 200 mu SNP could effectively alleviate Cd stress. Understanding the inhibitory effect of 30 mu cadmium on Alfalfa Seed Germination and growth. 2. Exogenous NO can alleviate the oxidative damage of Alfalfa under Cd stress by activating the antioxidant system, scavenging reactive oxygen species. Cd can induce ROS in seedlings, such as O2 - and H2O2, which lead to membrane lipid peroxidation, electrolyte leakage and oxidative stress. EC and MDA, H2O2 and O2 - were used to study membrane leakage in order to elucidate the plant damage caused by oxidative stress. The results showed that over time, excessive accumulation of these molecules induced by Cd led to oxidative damage in alfalfa seeds and inhibited seedling growth. Physiological changes and other mechanisms involved in plant inhibition or mitigation of abiotic or abiotic stress. In this study, the level of Pro in seedlings exposed to Cd stress was higher than that in the control seedlings. The level of Pro in seedlings exposed to Cd stress decreased further after the application of SNP, especially when the concentration of SNP was higher than 200 mu M, but long-term exposure to 20 mu. In response to and neutralizing ROS toxicity, endogenous antioxidant enzymes developed in plants include CAT, POD, SOD, APX, GR and other antioxidant enzymes. SOD protects cells from oxidation by promoting the transformation of superoxide free radicals. The most effective enzyme under stress was significantly inhibited, and its activity was significantly lower than that of control (CK), possibly because of the weak hydrogen bond of Zn2 + - SOD complex and the low solid content. Cd2 + could easily replace Zn2 + of SOD active site, so that the activity of SOD decreased. In this study, the accumulation of Cd LED to the significant production of H2O2 and O2 - and the decrease of SOD activity. The activity of SOD was increased by NO treatment, especially in the first three days after treatment. With the increase of SNP concentration, the activity of SOD was still higher than or equal to that of Cd treatment alone, which confirmed similar reports in early studies on rice and tomato seedlings. The activity of POD was higher than that of Cd alone, indicating that POD maintained higher activity in germination to scavenge H2O2. APX increased only 2 days before germination when SNP concentration was lower than 200 mu M, and decreased when SNP concentration was higher than 200 mu M. SNP treatment made APX activity significantly lower than that of Cd alone in late germination (3-5 days), and there was no significant change with the increase of SNP concentration. The results showed that APX scavenged ROS only at the early germination stage of Alfalfa seeds. CAT and APX scavenged ROS 4 days before germination. Cd stress made GR activity significantly lower than CK from the 2nd day of germination, while SNP treatment only increased GR activity on the 1st and 3rd day of germination, but showed no regularity with the increase of SNP concentration. 3. Exogenous NO can increase the content of storage substances and enhance the activity of related enzymes in Alfalfa Seedlings under Cd stress. The germination process is characterized by the hydrolysis of storage substances, such as carbohydrates and proteins, by hydrolases. Storage substances are hydrolyzed by hydrolases to provide energy for respiration and various anabolic reactions to form metabolites. The enzymes responsible for these storage substances, such as starch decomposition, are alpha-amylase and beta-amylase. It has been reported that Cd stress can limit the mobilization of reserve substances. The soluble protein, reducing sugar and soluble sugar content of alfalfa seeds were regulated by SNP activating alpha-amylase and beta-amylase. The activity of alpha-amylase and beta-amylase in alfalfa seeds were significantly decreased by 30 mu MCd stress, and the content of soluble protein and starch were also significantly decreased by the second day of treatment. The results showed that exogenous SNP could stimulate the germination of Alfalfa Seedlings under 30 mu MCd stress, and the contents of amylase, soluble protein and starch were significantly higher than those of alfalfa seedlings treated only with Cd. The results showed that exogenous NO could affect the amylase activity of pea seeds under Cd stress. The activity of exogenous NO, alpha-amylase and beta-amylase in seedlings treated with Cd increased significantly, and the contents of soluble starch and protein in seedlings treated with Cd were higher than those in seedlings treated only with Cd on the second day, which was beneficial to improving the germination of Alfalfa seedlings. The content of reducing sugar in seedlings was not significantly different under other treatments except SNP concentration at 25 and 100 mu M, and the production of reducing sugar was almost constant. 4. Exogenous NO significantly reduced the accumulation of Cd in alfalfa seeds and decreased the accumulation of Cd in alfalfa seeds. Cd, as one of the non-essential and harmful elements, can interfere with the balance of plants by competing with other trace and large amounts of nutrients in plants such as Ca2+ and K +, and can even be transported by water. This is related to the reduction of fresh and dry weight. Studies have reported that water content is being planted. In this study, as long as the seeds were exposed to Cd stress, the dry weight and fresh weight of the seeds were significantly affected as compared with CK seeds. Similar results were found in sunflower and sorghum seeds. Exogenous NO was reported to block the entry of heavy metals into plant cell walls, or to regulate them. Distribution and accumulation of excess Cd in plant cell wall. The results of this study were similar to those of rice seedling studies. It suggested that SNP might be one of the suitable compounds to protect seeds from heavy metal toxicity. 30 mu Cd did not significantly reduce the germination rate, but germinated. Hair index, SVI, root length and stem length were significantly affected by Cd toxicity; it was found that 30 mu CdCl_2 could induce the increase of Pro level, the excessive production of REC, MDA and ROS, and Cd could significantly inhibit the defense mechanism of alfalfa seeds by inducing the decrease of antioxidant enzyme activity; the activities of alpha-amylase and beta-amylase were significantly affected by Cd toxicity, resulting in the overproduction of REC, MDA and ROS. Soluble proteins, starches, sugars and reducing sugars were damaged by storage substances, and Cd also significantly affected the fresh and dry weight of seeds.
【學(xué)位授予單位】：蘭州交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：X173

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本文編號(hào)：2250280