水稻和小麦根尖细胞壁多糖的铝积累能力比较

采用水培法比较4种禾本科植物水稻(Oryza sativa L.)、玉米(Zea mays L.)、高粱(Sorghum bicolor(L.) Moench)和小麦(Triticum aestivum L.) 8个基因型的抗铝(Al)能力,并对他们在Al积累后细胞壁的多糖组分进行分析。结果显示,在5～200μmol/L Al处理下,水稻抗Al能力较强,而小麦抗Al能力较弱。在50μmol/L Al处理下,小麦根尖的果胶和半纤维素1含量的增幅明显高于水稻。水稻基因型‘日本晴’与‘浙辐802’的细胞壁Al含量分别占根尖总Al含量的78. 7%和91. 6%;小麦基因型‘扬麦18’与‘扬麦16’Al含量分别占根尖总Al含量的64.9%和72.1%。Al吸附-解吸实验结果显示,小麦根尖细胞壁上Al的吸附量高于水稻。研究结果表明,细胞壁是Al积累的主要部位,对Al敏感的水稻和小麦基因型细胞壁中的Al主要分布在果胶中;而对Al耐性较强的水稻和小麦基因型细胞壁中的Al主要分布在半纤维素1中。     

小麦根系对铝毒的反应及其与根细胞壁组分和细胞壁对铝的吸附-解吸性能的关系

研究了小麦根系对铝毒的反应与不同根段细胞壁的组分及细胞壁对铝的吸附解吸性能的关系。结果表明,30μmol/LAlCl3可迅速抑制根系伸长,在铝处理30h时其根长仅为对照的30.2%;小麦根系相对伸长率随着铝浓度的提高而急剧降低,30μmol/LAlCl3处理24h对根系伸长的抑制率高达70.9%。小麦根系中距根尖0~10mm根段的铝含量和细胞壁中果胶糖醛酸含量明显高于距根尖10~20mm根段;距根尖0~10mm根段细胞壁对铝的吸附量明显大于距根尖10~20mm根段,而前者吸附态铝的解吸率低于后者;铝浓度从10μmol/L提高到20μmol/L时细胞壁对铝的吸附量增加,但对铝的解吸没有明显影响。采用1.0mol/LNH3·H2O对细胞壁预处理2h降低果胶甲基酯化程度后,铝吸附量降低了20.9%,但对铝解吸率没有影响。由此可见,小麦根尖是铝毒的主要位点,细胞壁果胶含量和果胶甲基酯化程度对小麦不同根段细胞壁对铝的吸附、积累具有重要作用,铝与细胞壁的结合是根系对铝毒胁迫反应的重要原因。     

边缘细胞对荞麦根尖铝毒的防护效应和对细胞壁多糖的影响

以2个荞麦(Fygopyrum esculentum Moench)基因型‘江西荞麦’(耐性)和‘内蒙荞麦’(敏感)为材料,采用悬空培养(保持边缘细胞附着于根尖和去除根尖边缘细胞),研究边缘细胞对根尖铝毒的防护效应以及对细胞壁多糖组分的影响。结果表明,铝毒抑制荞麦根系伸长,导致根尖Al积累。去除边缘细胞的根伸长抑制率和根尖Al含量高于保留边缘细胞的根。去除边缘细胞使江西荞麦和内蒙荞麦根尖的酸性磷酸酶(APA)活性显著升高,前者在铝毒下增幅更大。同时,铝毒胁迫下去除边缘细胞的根尖果胶甲酯酶(PME)活性和细胞壁果胶、半纤维素1、半纤维素2含量显著高于保留边缘细胞的酶活性和细胞壁多糖含量。表明边缘细胞对荞麦根尖的防护效应,与其阻止Al的吸收,降低根尖细胞壁多糖含量及提高酸性磷酸酶活性有关,以此缓解Al对根伸长的抑制。     

外源钾对铁胁迫下水稻细胞壁多糖含量及耐铁性的影响

以耐铁毒型水稻品种协优9308和铁毒敏感型水稻品种Ⅱ优838为实验材料,采用溶液培养法研究250mg.L-1Fe2+(EDTA-Fe2+)胁迫下,不同钾水平对两种水稻的生长特性、酸性磷酸酶(APA)、果胶甲酯酶(PME)、根系果胶含量、半纤维素1含量以及半纤维素2含量的影响。结果表明,经250mg.L-1Fe2+处理7d和14d后,协优9308和Ⅱ优838的相对根长明显下降,APA、PME的活性显著升高,果胶含量、半纤维素1含量、半纤维素2含量显著增加,Ⅱ优838酶活性及细胞壁多糖含量提高幅度较大,表现出其铁毒敏感性,并且随着处理时间的延长,铁胁迫对两种水稻相对根长,PME活性,HC1含量及HC2含量的影响越显著,但APA活性和果胶含量则没有明显变化。加入外源钾可以不同程度的降低酶活性及细胞壁多糖含量,外源钾浓度为200mg.L-1,对水稻相对根长,APA活性,HC1含量缓解效果较好;外源钾浓度为400mg.L-1,对PME活性,果胶含量缓解效果较好。随着外源钾浓度升高,水稻铁毒症状得到不同程度的缓解,但钾浓度高于200mg.L-1又会对水稻造成新的胁迫。由此推测,水稻通过提高根系细胞壁多糖含量来增加根尖铁的结合位点,以及细胞壁的厚度和刚性,并降低细胞壁的伸展性,使根细胞的伸长受抑,从而提高其铁耐性。     

茶树根细胞壁不同组分对铅的吸附性能及其功能团的傅里叶红外光谱学研究

选择我国重要的经济作物之一茶树(Camellia sinensis L.)为研究对象,考察了茶树根细胞壁中不同多糖组分在吸附铅(Pb)过程中的作用差异以及与其发生交互作用的主要功能团。结果表明,在茶树根细胞壁吸附Pb过程中,绝大多数的Pb(68.42%)是吸附在纤维素以及木质素上;其次是果胶(20%)、半纤维素2类(5.26%);半纤维素1类的贡献可以忽略不计。同时,通过细胞壁不同组分吸附Pb前后的傅立叶红外光谱表征结果得出,在吸附Pb的过程中,果胶中起作用的功能团主要有羟基、羧基;半纤维素1类中起作用的功能团主要是羧基;半纤维素2类中起作用的功能团主要为羟基。     

铝对秋葵、小麦种子萌发和幼苗生长的影响

以不同抗铝小麦（Triticum aestivum L．）基因型：Carazinho（抗铝型）和Egret（铝敏感型）为参比,研究了铝胁迫对秋葵（Hibiscus moscheutos L．）种子萌发和幼苗生长的影响。结果表明：秋葵和小麦种子的萌发对铝胁迫不敏感;高浓度的AlCl3（50μmol／L）显著抑制主根和侧根伸长,但对侧根数目的影响较小;两种植物的主根伸长对铝胁迫的差异不显著,而秋葵侧根对铝毒的抗性比两个供试的小麦基因型强;50μmol／L的AlCl3显著降低两个小麦基因型的根系生物量,但秋葵的根系生物量与对照比变化不大。表明秋葵幼苗的抗铝性强于两个小麦品种,铝对秋葵、小麦侧根和主根的生长影响不同。     

硼添加对铝胁迫栝楼生长和生理的影响

为揭示硼对缓解栝楼(Trichosanthes kirilowii Maxim.)铝(Aluminum)毒害的生理机制,以耐铝性强的安国栝楼和耐铝性弱的浦江栝楼为材料,研究了50μmol/L硼酸(H₃BO₃)对300μmol/L Al³⁺胁迫下栝楼幼苗生长、铝积累、抗氧化能力和细胞壁组分的影响。结果表明：铝胁迫下,植株的根长、株高、鲜重和干重降低,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性受到显著抑制,安国栝楼、浦江栝楼根尖丙二醛(MDA)含量分别增加256.1%、278.2%,细胞壁多糖含量、果胶甲酯酶(PME)活性、根尖铝积累量显著提高,果胶甲基酯化度(DM)和3-脱氧-D-甘露-辛酮糖酸(KDO)含量降低。外源硼可以缓解铝胁迫对栝楼幼苗生长的抑制作用,安国与浦江栝楼的抗氧化酶活性显著提升,MDA含量、细胞壁多糖含量、PME酶活性均降低,安国栝楼果胶DM值恢复至正常水平的91.5%,浦江栝楼KDO含量较单铝处理组上升52.0%,活性铝结合位点减少,有效降低了根尖铝含量并维持其形态结构。因...     

缺钙诱发大白菜干烧心与细胞壁结构分变化的关系

缺钙培养诱导大白菜干烧心发生,测定心叶组织细胞壁各成分量的变化。结果表明,随着缺钙天数增加,果胶、半纤维素１（ＨＣ１）和纤维素的含量呈平稳上升,到缺钙处理后第２４天时达到高峰,随后急剧下降,而半纤维素２（ＨＣ２）的含量变化不大;醛酸在果胶中的含量逐渐呈下降趋势,在ＨＣ２中的含量先升后降,而在ＨＣ１和纤维素中的含量变化不不大。总糖在ＨＣ１和经纱中的含量呈下降趋势,在果胶中的含量先升后降,而在ＨＣ２中     

细胞壁代谢与琯溪蜜柚果实成熟过程汁胞粒化的关系

以易发生汁胞粒化的老龄树和不易发生汁胞粒化的适龄树的琯溪蜜柚（Citrus grandis（L．）Osbeck‘Guanximiyou’1果实为材料,研究了果实成熟过程中汁胞粒化发生与细胞壁代谢的关系。结果表明：老龄树果实的汁胞粒化指数随着果实成熟而上升。在汁胞粒化发生过程中,汁胞维持较低的细胞壁降解酶[果胶甲酯酶（PE）、多聚半乳糖醛酸酶（PG）、纤维素酶（Cx）]活性,保持较高的细胞壁物质（原果胶、纤维素、半纤维素）含量;尤其在汁胞粒化的起动阶段和加快阶段,纤维素、半纤维素含量极显著增加。相反,适龄树果实的汁胞粒化指数在果实成熟过程中变化不大,汁胞中细胞壁降解酶活性较高,促进原果胶、纤维素、半纤维素等细胞壁物质的降解,保持较低的细胞壁物质含量,使汁胞发育正常、柔软多汁。这说明PE、PG、Cx活性和原果胶、纤维素、半纤维素含量与錧溪蜜柚汁胞粒化密切相关。     

硅对盐胁迫下枣树组织培养苗细胞壁形成和相关酶活性的影响

盐胁迫（75mmol·L^-1 NaCl）下,枣树微茎段外植体成活率、生根率及枣苗的侧根条数和长度、苗高、单株重量均较对照显著减小;盐胁迫下加硅（Si）（0．75mmol·L^-1 KSiO3）,枣苗的前述指标与对照无显著性差异。盐胁迫下,枣组织培养生根苗细胞壁提取率显著下降,细胞壁中蛋白和低分子量果胶含量显著降低,EDTAU溶性果胶和碱溶性果胶含量显著提高,半纤维素和纤维素含量降低;盐胁迫下加Si,枣苗细胞壁提取率显著提高,细胞壁主要戍分的含量水平与对照相近。与盐胁迫下相比,盐胁迫下加Si,虽然枣苗果胶甲酯酶（PME）和多聚半乳糖醛酸酶（PG）活性升高未达显著性差异水平,但纤维素酶（Cx）活性显著降低,3种水解酶活性的比值均显著增大,细胞壁共价结合态H^＋-ATP酶活性显著升高。结果说明,提高培养基可溶性Si水平,可显著改善受盐胁迫枣苗细胞壁水解酶的活性平衡、组分含量的均衡及细胞壁内外溶质的适应性分配,从而为枣苗较好生长奠定了基础。     

Nitric oxide enhances aluminum tolerance by affecting cell wall polysaccharides in rice roots

Nitric oxide (NO) is a key signal molecule involved in many physiological processes in plants. To study the mechanisms of exogenous NO contribution to alleviate the aluminum (Al) toxicity, roots of rice (Oryza sativa) seedlings pre-treated with sodium nitroprusside (SNP, a NO donor) were used to investigate the effect of Al in this study. Results indicated that NO alleviated the lipid peroxidation induced by Al and promoted the root elongation, whereas butylated hydroxyanisole (BHA), an efficient lipophilic antioxidant, alleviated the lipid peroxidation only. Rice seedling roots pre-treated with SNP followed by Al treatment had lower contents of pectin and hemicellulose, lower Al accumulation in root tips and cell walls, higher degree of methylation of pectin and lower wall Al-binding capacity than the roots with Al treatment only. Therefore, the decreased Al accumulation in the cell walls of rice roots is likely to be the reason for the NO-induced increase of Al tolerance in rice, and it seems that exogenous NO enhanced Al tolerance in rice roots by decreasing the contents of pectin and hemicellulose, increasing the degree of methylation of pectin, and decreasing Al accumulation in root cell walls.     

Cell wall polysaccharides are specifically involved in the exclusion of aluminum from the rice root apex

Rice (Oryza sativa) is the most aluminum (Al)-resistant crop species among the small-grain cereals, but the mechanisms responsible for this trait are still unclear. Using two rice cultivars differing in Al resistance, rice sp. japonica 'Nipponbare' (an Al-resistant cultivar) and rice sp. indica 'Zhefu802' (an Al-sensitive cultivar), it was found that Al content in the root apex (0-10 mm) was significantly lower in Al-resistant 'Nipponbare' than in sensitive 'Zhefu802', with more of the Al localized to cell walls in 'Zhefu802', indicating that an Al exclusion mechanism is operating in 'Nipponbare'. However, neither organic acid efflux nor changes in rhizosphere pH appear to be responsible for the Al exclusion. Interestingly, cell wall polysaccharides (pectin, hemicellulose 1, and hemicellulose 2) in the root apex were found to be significantly higher in 'Zhefu802' than in 'Nipponbare' in the absence of Al, and Al exposure increased root apex hemicellulose content more significantly in 'Zhefu802'. Root tip cell wall pectin methylesterase (PME) activity was constitutively higher in 'Zhefu802' than in 'Nipponbare', although Al treatment resulted in increased PME activity in both cultivars. Immunolocalization of pectins showed a higher proportion of demethylated pectins in 'Zhefu802', indicating a higher proportion of free pectic acid residues in the cell walls of 'Zhefu802' root tips. Al adsorption and desorption kinetics of root tip cell walls also indicated that more Al was adsorbed and bound Al was retained more tightly in 'Zhefu802', which was consistent with Al content, PME activity, and pectin demethylesterification results. These responses were specific to Al compared with other metals (CdCl(2), LaCl(3), and CuCl(2)), and the ability of the cell wall to adsorb these metals was also not related to levels of cell wall pectins. All of these results suggest that cell wall polysaccharides may play an important role in excluding Al specifically from the rice root apex.     

Putrescine alleviates aluminum toxicity in rice (Oryza sativa) by reducing cell wall Al contents in an ethylene‐dependent manner

Aluminum (Al³⁺) toxicity in acidic soils limits crop productivity worldwide. In this study, we found that putrescine (PUT) significantly alleviates Al toxicity in rice roots. The addition of 0.1 mM PUT promoted root elongation and reduced the Al content in the root apices of Nipponbare (Nip) and Kasalath (Kas) rice under Al toxicity conditions. Exogenous treatment with PUT reduced the cell wall Al content by reducing polysaccharide (pectin and hemicellulose) levels and pectin methylesterase (PME) activity in roots and decreased the translocation of Al from the external environment to the cytoplasm by downregulating the expression of OsNRAT1, which responsible to encode an Al transporter protein Nrat1 (Nramp aluminum transporter 1). The addition of PUT under Al toxicity conditions significantly inhibited ethylene emissions and suppressed the expression of genes involved in ethylene biosynthesis. Treatment with the ethylene precursor 1‐aminocylopropane‐1‐carboxylic acid (ACC) significantly improved ethylene emission, inhibited root elongation, increased the Al accumulation in root tips and the root cell wall, and increased cell wall pectin and hemicellulose contents in both rice cultivars under Al toxicity conditions. The ethylene biosynthesis antagonist aminoethoxyvinylglycine (AVG, inhibitor of the ACC synthase) had the opposite effect and reduced PME activity. Together, our results show that PUT decreases the cell wall Al contents by suppressing ethylene emissions and decreases the symplastic Al levels by downregulating OsNRAT1 in rice.     

Phosphorus deficiency enhances aluminum tolerance of rice (Oryza sativa) by changing the physicochemical characteristics of root plasma membranes and cell walls

The negative charge at the root surface is mainly derived from the phosphate group of phospholipids in plasma membranes (PMs) and the carboxyl group of pectins in cell walls, which are usually neutralized by calcium (Ca) ions contributing to maintain the root integrity. The major toxic effect of aluminum (Al) in plants is the inhibition of root elongation due to Al binding tightly to these negative sites in exchange for Ca. Because phospholipid and pectin concentrations decrease in roots of some plant species under phosphorus (P)-limiting conditions, we hypothesized that rice (Oryza sativa L.) seedlings grown under P-limiting conditions would demonstrate enhanced Al tolerance because of their fewer sites on their roots. For pretreatment, rice seedlings were grown in a culture solution with (+P) or without (−P) P. Thereafter, the seedlings were transferred to a solution with or without Al, and the lipid, pectin, hemicellulose, and mineral concentrations as well as Al tolerance were then determined. Furthermore, the low-Ca tolerance of P-pretreated seedlings was investigated under different pH conditions. The concentrations of phospholipids and pectins in the roots of rice receiving −P pretreatment were lower than those receiving +P pretreatment. As expected, seedlings receiving the −P pretreatment showed enhanced Al tolerance, accompanied by the decrease in Al accumulation in their roots and shoots. This low P-induced enhanced Al tolerance was not explained by enhanced antioxidant activities or organic acid secretion from roots but by the decrease in phospholipid and pectin concentrations in the roots. In addition, low-Ca tolerance of the roots was enhanced by the −P pretreatment under low pH conditions. This low P-induced enhancement of low-Ca tolerance may be related to the lower Ca requirement to maintain PM and cell wall structures in roots of rice with fewer phospholipids and pectins.     

Growth and cell wall properties of two wheat cultivars differing in their sensitivity to aluminum stress

The present study was conducted to investigate the cell wall properties in two wheat (Triticum aestivum L.) cultivars differing in their sensitivity to Al stress. Seedlings of Al-resistant, Inia66 and Al-sensitive, Kalyansona cultivars were grown in complete nutrient solutions for 4 days and then subjected to treatment solutions containing Al (0, 50 microM) in a 0.5 mM CaCl(2) solution at pH 4.5 for 24 h. Root elongation was inhibited greatly by the Al treatment in the Al-sensitive cultivar compared to the Al-resistant cultivar. The Al-resistant cultivar accumulated less amount of Al in the root apex than in the Al-sensitive cultivar. The contents of pectin and hemicellulose in roots were increased with Al stress, and this increase was more conspicuous in the Al-sensitive cultivar. The molecular mass of hemicellulosic polysaccharides was increased by the Al treatment in the Al-sensitive cultivar. The increase in the content of hemicellulose was attributed to increase in the contents of glucose, arabinose and xylose in neutral sugars. Aluminum treatment increased the contents of ferulic acid and p-coumaric acid especially in the Al-sensitive cultivar by increasing the activity of phenylalanine ammonia lyase (PAL, EC 4.3.1.5). Aluminum treatment markedly decreased the beta-glucanase activity in the Al-sensitive cultivar, but did not exert any effect in the Al-resistant cultivar. These results suggest that the modulation of the activity of beta-glucanase with Al stress may be involved in part in the alteration of the molecular mass of hemicellulosic polysaccharides in the Al-sensitive cultivar. The increase in the molecular mass of hemicellulosic polysaccharides and ferulic acid synthesis in the Al-sensitive cultivar with Al stress may induce the mechanical rigidity of the cell wall and inhibit the elongation of wheat roots.     

Changes in cell-wall properties of wheat (Triticum aestivum) roots during aluminum-induced growth inhibition

The effects of aluminum (Al) on root elongation, the mechanical extensibility of the cell wall, and the amount of cell-wall polysaccharides in the roots of Al-resistant (Atlas 66) and Al-sensitive (Scout 66) cultivars of wheat ( Triticum aestivum L.) were examined. Exposure to 10 μ M AlCl₃ for 6 h inhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wall in the roots of both cultivars, but prominently only in the roots of Scout 66. The amount of hemicellulose in the 10-mm region of root apex of Scout 66 was increased by the exposure to Al, especially in the apical regions. Al did not influence the neutral sugar composition of either pectin or hemicellulose in Scout 66 roots. However, Al increased the weight-average molecular mass of hemicellulosic polysaccharides and the amounts of wall-bound ferulic and diferulic acids in Scout 66 roots. These findings suggest that Al modifies the metabolism of cell-wall components and thus makes the cell wall thick and rigid, thereby inhibiting the growth of wheat roots.     

PARVUS affects aluminium sensitivity by modulating the structure of glucuronoxylan in Arabidopsis thaliana

Glucuronoxylan (GX), an important component of hemicellulose in the cell wall, appears to affect aluminium (Al) sensitivity in plants. To investigate the role of GX in cell‐wall‐localized xylan, we examined the Arabidopsis thaliana parvus mutant in detail. This mutant lacks α‐D‐glucuronic acid (GlcA) side chains in GX and has greater resistance to Al stress than wild‐type (WT) plants. The parvus mutant accumulated lower levels of Al in its roots and cell walls than WT despite having cell wall pectin content and pectin methylesterase (PME) activity similar to those of WT. Our results suggest that the altered properties of hemicellulose in the mutant contribute to its decreased Al accumulation. Although we observed almost no differences in hemicellulose content between parvus and WT under control conditions, less Al was retained in parvus hemicellulose than in WT. This observation is consistent with the finding that GlcA substitutions in WT GX, but not mutant GX, were increased under Al stress. Taken together, these results suggest that the modulation of GlcA levels in GX affects Al resistance by influencing the Al binding capacity of the root cell wall in Arabidopsis.     

不同浓度硝态氮供应下小麦生长、硝态氮累积及根系钙信号特征

以小麦品种‘石麦15’和‘衡观35’为材料进行营养液水培试验,研究不同浓度硝态氮供应对小麦苗期根系形态、钙离子流特征及钙调蛋白(CaM)含量的影响。结果表明,与适宜浓度硝态氮处理(2.5mmol/L)相比,无外源硝态氮供应时小麦地上部鲜重、硝态氮含量均降低,侧根数量显著减少;高浓度硝态氮处理(50mmol/L)下两个小麦品种地上部硝态氮含量升高,根系总长度降低,‘石麦15’侧根数量减少。无硝态氮和高浓度硝态氮处理下,根系中钙调蛋白含量降低,且‘衡观35’的降低幅度大于‘石麦15’。无外源硝态氮供应时小麦根尖表现出较为明显的钙离子外流特征;与适宜浓度硝态氮处理相比,高硝态氮处理下小麦根尖Ca2+的内流速度显著下降。说明硝态氮供应不足和高浓度硝态氮供应会影响小麦根系生长,根系Ca2+外流或Ca2+内流速度下降,CaM含量减少,Ca2+/CaM可能介导硝态氮调控小麦根系生长发育。     

The kinetics of aluminum adsorption and desorption by root cell walls of an aluminum resistant wheat (Triticum aestivum L.) cultivar

In the present study, root cell walls were extracted from an Al-resistant wheat (Triticum aestivum L.) cultivar, Atlas 66 to investigate the effect of cell-wall properties on the kinetics of Al adsorption and desorption. Nearly all the Al adsorbed was desorbed by 2.5 mM CaCl₂ at pH 4.5, indicating that most of Al ions were electrically bound to cell wall materials. After the cell walls were treated with 1% pectinase for 30 min to degrade part of pectin, the total amount of Al absorbed was decreased by about 50%, indicating that pectin in the cell walls played an important role in binding Al. When the cell walls were preincubated in 1 and 10 mM malate solution overnight to mimic the organic acid secretion by the roots of wheat, the total amount of Al adsorbed was decreased by 60 and 80%, respectively, suggesting that the malate secreted in response to Al stress not only detoxifies Al by its chelating effect, but also reduce the cell walls' capacity to bind Al.