铝胁迫对小麦根尖细胞蛋白质及苹果酸分泌的影响

以一对近等位基因小麦品系(ET8和ES8)为材料,研究了铝胁迫条件下根系生长情况,根尖铝含量,根尖细胞质蛋白组分以及铝胁迫下两个小麦品系苹果酸分泌的差异。结果表明,小麦品系ET8的耐铝性明显高于ES8;而ET8根尖铝含量则明显低于ES8;50mol/L铝处理24h后ES8小麦的细胞质蛋白组成受到明显影响,而ET8则无明显影响。由于铝胁迫条件下ET8分泌的苹果酸的量明显高于ES8,因此可以认为,分泌的苹果酸一方面与铝结合使其无毒化;另一方面将铝排斥于根尖细胞外,从而阻止铝进入细胞质内对细胞产生毒害作用。     

铝胁迫下不同耐铝性小麦根际pH值变化及其与耐铝性的关系

Al3＋是植物铝毒害的主要形态,而其活性受环境pH值的影响,H＋-ATPase通过调节根的质子分泌改变根际pH值。为探讨铝胁迫下根际pH值变化与小麦耐铝性的关系,以小麦品种ET8（耐铝型）、ES8（铝敏感型）为试验材料,采用溶液培养的方法对铝胁迫下根际pH值及根尖H＋-ATPase活性变化进行了研究。结果表明,铝处理条件下,小麦根际pH值随培养时间的延长而升高;随培养液中铝浓度的增加,根际pH值上升幅度下降,相同铝浓度处理条件下ET8根际pH值显著高于ES8。根际pH值与根尖铝含量呈极显著负相关（R2=0.932 1）,与根相对伸长率呈极显著正相关（R2=0.858 5）,表明小麦通过提高根际pH值降低根尖铝含量,减轻铝毒害。根尖H＋-ATPase活性随铝处理浓度升高而显著降低,100 μmol·L-1Al处理24 h ET8和ES8根尖H＋-ATPase活性分别为各自无铝处理的69.8%和60.0%,根尖H＋-ATPase相对活性与根际pH值呈极显著负相关（R2=0.831 9）。温度显著影响根的伸长,低温处理（9 ℃）根际pH值显著高于常温处理（25 ℃）,而根尖铝含量却显著低于常温处理。表明小麦通过根尖H＋-ATPase提高根际pH值降低铝毒害。综上所述,铝胁迫下小麦可通过提高根际pH值减轻铝毒害,不同耐铝性小麦品种根际pH值的显著差异是耐铝性差异显著的     

小麦根尖细胞壁对铝的吸附/解吸特性及其与耐铝性的关系

研究了耐铝性明显差异的2个小麦基因型西矮麦1号(耐性)和辐84系(敏感)根系对铝毒胁迫的反应与根尖细胞壁组分以及细胞壁对铝的吸附和解吸的关系。结果表明,30mol/L.AlCl3可迅速抑制小麦根系伸长,但对辐84系根系伸长的抑制更为明显,且小麦根系相对伸长率随着铝浓度的提高而急剧降低。在30mol/L.AlCl3处理24h后,西矮麦1号根系伸长的抑制率为33.3%,而辐84系根系伸长的抑制率高达70.9%。小麦距根尖0～10.mm根段的铝含量和细胞壁中果胶糖醛酸含量显著高于10～20.mm根段,且前者对铝的累积吸附量明显大于后者;在0～10.mm根段,敏感基因型果胶含量高于耐性基因型,其根尖含铝量及根尖细胞壁对铝的吸附量都要大于后者。采用1.0.mol/L.NH3.H2O对细胞壁预处理2.h降低果胶甲基酯化程度后,耐性和敏感基因型根尖细胞壁对铝的累积吸附量分别降低了17.1%和20.9%,但对铝的累积解吸率没有影响。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可能是导致不同小麦基因型根尖细胞壁对铝吸附量、铝积累量的差异及其对铝毒胁迫反应的差异的重要原因。     

铝对小麦根尖细胞壁过氧化物酶活性和过氧化氢含量的影响

以2个小麦基因型鉴-864(耐性)和扬麦5号(敏感)为材料,采用溶液培养方法研究了铝胁迫下小麦根系伸长、根尖铝含量、根尖细胞壁过氧化物酶活性和H2O2含量的变化。结果表明,随着铝浓度的提高,小麦根系伸长受铝抑制程度加剧,根尖铝含量也明显升高;但敏感基因型根尖铝含量较高,根系伸长受抑程度更为明显。在铝胁迫下,2个小麦基因型根尖可溶态愈创木酚过氧化物酶(GPX)和松柏醇过氧化物酶(CAPX)活性没有显著变化,细胞壁离子键结合态GPX和CAPX的活性则随着铝浓度的提高而显著升高,H2O2含量也呈现类似的趋势;而敏感基因型过氧化物酶活性升高和H2O2积累更为明显。因此,铝胁迫下,小麦敏感基因型根尖细胞壁离子键结合态GPX和CAPX活性升高而引起H2O2积累,促进根系木质化和细胞壁氧化交联,导致根细胞壁刚性提高而伸展能力降低,是其根系伸长受到严重抑制的原因。     

外源NO对采后绿芦笋木质化和抗氧化能力的影响

为探讨NO处理对采后绿芦笋木质化合成的调控机理。以0.2mmol/L的硝普钠为一氧化氮供体,以蒸馏水处理为对照,研究了NO对采后绿芦笋总酚、木质素含量;木质素合成关键酶(苯丙氨酸解氨酶、肉桂醇脱氢酶、过氧化物酶、多酚氧化酶);抗氧化能力(1,1-二苯基-2-三硝基苯肼自由基清除率、超氧阴离子自由基(O2.-)清除率、羟基自由基(·OH)清除率)及膜透性的影响,结果表明,与对照相比,NO处理可延缓采后绿芦笋木质素含量和膜透性的增加,抑制肉桂醇脱氢酶和多酚氧化酶活性,增强抗氧化能力,诱导过氧化物酶活性增强,但对苯丙氨酸解氨酶活性和总酚含量的影响不显著。说明NO处理是通过抑制肉桂醇脱氢酶和多酚氧化酶活性、提高抗氧化能力而延缓采后绿芦笋的木质化进程。研究结果可为NO在绿芦笋保鲜中的应用提供理论依据和技术方法。     

铝胁迫下硝普钠对黑麦和小麦根尖细胞壁铝吸附的影响

用一氧化氮供体硝普钠(sodium nitroprusside,SNP)处理铝胁迫下的黑麦和小麦幼苗,探讨铝胁迫和铝胁迫下外源NO对黑麦和小麦根尖细胞壁铝吸附的影响。结果表明:铝显著抑制黑麦和小麦根的伸长生长,小麦受抑制更为严重;SNP处理可缓解铝对黑麦和小麦根伸长生长的抑制作用,1 mmol/L SNP处理最有效。小麦根尖对铝的吸附量和吸附速率显著高于黑麦的,1 mmol/L SNP处理显著降低小麦和黑麦细胞壁对铝的吸附量,使根尖铝含量显著下降。铝与根尖细胞壁的结合是导致植物铝毒害的重要原因,而降低根尖细胞壁对铝的吸附是外源NO缓解铝毒害的重要机制。     

铝毒胁迫下磷对荞麦根系铝形态和分布的影响

以2个荞麦（Fagopyrum esculentum Moench）品种＂江西荞麦＂（铝耐性）和＂内蒙荞麦＂（铝敏感）为材料,采用水培法,研究铝毒胁迫下磷对荞麦根系总铝和单核2种形态以及Al在根尖和细胞壁中的分布情况的影响。结果表明,与200μmol/L Al处理相比,1.0mmol/L磷预处理分别使江西荞麦和内蒙荞麦的相对根长增加了24.4%和35.9%,根系总Al含量分别降低了18.2%和22.5%,根系单核Al含量分别降低了95%和63.2%。根尖细胞壁荧光检测结果为在单Al胁迫下细胞壁的荧光强度最大,1.0mmol/L磷预处理大幅度减弱细胞壁的荧光强度。表明外源磷供应可降低根系总Al和单核Al含量,使毒性形态的铝转化为无毒形态,以及减少Al在根尖以及细胞壁的积累,以缓解Al对根伸长的抑制,提高荞麦根系的抗铝毒害能力。     

铝胁迫下植物根尖细胞壁组成物质变化抑制根伸长的生理机制研究

根伸长受抑制是植物受铝毒害的主要症状,铝诱导的细胞壁组成物质的变化是其主要原因。本文主要对铝胁迫下植物根尖细胞壁组成物质如木质素、 胼胝质、 纤维素、 半纤维素、 果胶、 细胞壁多糖蛋白及相关代谢酶类在铝胁迫下的变化对根伸长的影响及生理机理的研究进展进行了综述,明确了铝胁迫诱导的植物根尖细胞壁组成物质含量、 比例及结构的变化导致细胞壁刚性降低,从而抑制细胞伸长,最终抑制根伸长。本文还指出,鉴于缺乏对同一植物甚至同一个种类的植物根尖细胞壁各主要组成物质铝胁迫下变化的系统研究,不能对造成该植物根伸长受抑制的原因做出全面合理的解释,所以今后应侧重于铝胁迫下各细胞壁组分变化在抑制根伸长中的贡献率的研究,尤其要针对主要粮食作物进行系统研究,以有效解决铝胁迫造成的产质量降低。     

酸铝胁迫对栝楼根系生长及铝积累的影响

针对南方酸性红壤对作物的生长造成的不利影响,采用水培方式,研究酸铝环境0、100、300、500、1000μmol·L-1Al3＋pH4.5,处理7d对长兴栝楼根系生长及铝积累的影响。测定指标包括根系活力、质膜透性、抗氧化酶类活性（过氧化物酶POD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX、愈创木酚过氧化物酶GPX、超氧化物歧化酶SOD）及其同工酶、过氧化氢（H2O2）含量、根尖铝含量的影响。结果表明：随着铝处理浓度升高,根系活力增大,根系质膜透性无显著变化;POD、CAT、APX酶活升高,GPX和SOD活性降低,多种抗氧化酶都有多条同工酶谱带出现;根尖相对铝含量升高,桑色素染色情况显示,荧光梯度与铝含量测定结果一致,并观察到根尖以上根毛处细胞凸起较之平整排列的根细胞更容易积累铝。栝楼对南方酸性红壤具有较强的适应能力,其体内抗氧化酶系统及根尖吸收、积累铝的机制对缓解铝毒害起着重要作用。     

黑麦品种间耐铝差异性机制研究

采用室内模拟方法,研究了铝诱导黑麦根系分泌有机酸、根尖磷对铝的固定作用。结果表明,在铝胁迫下冬牧品种（Win）相对根伸长率高于King品种。在铝胁迫下,经磷预处理的根尖铝和磷含量增加,且以Win品种根尖中的Al、P含量较高,说明根尖磷对铝的固定是黑麦耐铝机制之一。另一方面,在铝胁迫下,两品种根系均分泌柠檬酸和苹果酸,且Win的分泌速率较高。有机酸的分泌随着铝处理浓度（10、30、50 mol/L）和时间（0.5、3、6、9、12 h）的增加而增加,但在低温（4C）下柠檬酸分泌量显著减少。Al处理0.5 h后苹果酸已明显分泌,而柠檬酸的分泌在铝处理6 h后才明显增加。在铝处理前,进行缺磷预处理（3 d）不能增加有机酸的分泌,10 mol/L的La3+、Cu2+、Ni3+也不能诱导根系分泌有机酸。说明铝诱导根系专一性分泌有机酸也是黑麦品种间耐铝性差异的机制。     

Changes in Cell Wall Polysaccharides and Hydroxycinnamates in Wheat Roots by Aluminum Stress at Higher Calcium Supply

The present study was conducted to investigate the cell-wall polysaccharides and hydroxycinnamates in wheat plants (Triticum aestivum L.) under aluminum (Al) stress at a higher level of calcium (Ca) supply. Seedlings were grown in nutrient solution for 7 d and then subjected to treatment solutions containing Al (0 or 100 μM) and Ca (0 or 2500 μM) in a 500 μM CaCl ₂ solution at pH 4.5 for 8 d. Calcium treatment (2500 μM) improved root growth significantly under Al-stress conditions. The contents of pectin and hemicellulose in roots were increased under Al-stress conditions, and this increase was conspicuous in the hemicellulosic fraction. The increase in the hemicellulose was attributed to increases in arabinose, xylose, and glucose in neutral sugars. High Ca treatment decreased these contents in Al-stressed cell walls. Aluminum treatment increased the content of ferulic acid, whereas Ca treatment with Al reduced the content. These results suggest that Al may modify the mechanical properties of cell-wall polysaccharides by enhancing the synthesis of arabinoxylan, β-glucan, and ferulic acid in the cell wall. High Ca treatment may maintain the normal synthesis of these materials even under Al-stress conditions.     

Genotypic Differences Among Plant Species in Response to Aluminum Stress

Abstract

Genotypic differences in aluminum (Al) resistance in rye (Secale cereale L.), triticale (X Triticosecale Wittmack), wheat (Triticum aestivum L.), and buckwheat (Fygopyrum esculentum Moench) were examined using a compartmental hydroponic system. Four-day-old seedlings were grown for 24 h in 0.5 mM CaCl₂ (pH 4.5) containing 0 or 50 μM Al. Relative root elongation (RRE) at 50 μM Al. (as a percentage of that at 0 Al) was used as the index of Al resistance. On average, rye exhibited the highest Al resistance, followed by buckwheat, triticale, and wheat. However, triticale displayed the greatest genotypic differences. Al content in the root tips of triticale breeding lines negatively correlated with RRE (r = 0.5, P < 0.01), implying that the Al exclusion mechanism contributed to Al resistance. Furthermore, high Al resistance in buckwheat correlated well with the growth habitats of buckwheat, indicating that adaptation mechanisms giving good Al resistance have evolved in buckwheat. All of these results suggested that it is possible to obtain greater Al resistance in plants by screening current existing cultivars. The selection of new cultivars with increased Al resistance and sensitivity will provide important material for further studies exploring Al phytotoxic and resistant mechanisms.     

Assessment of aluminum sensitivity of maize cultivars using roots of intact plants and excised root tips

Maize cultivars (Zea mays L.) were evaluated for their aluminum (Al) sensitivity using intact plants and excised root tips exposed to 25 μM Al in nutrient solution of low ionic strength and pH 4.3. Aluminum supply increased callose formation and Al concentrations in root tips of intact plants as well as in excised root tips. Using intact plants, differences in Al sensitivity among cultivars could be characterized by Al‐induced callose formation, Al‐induced inhibition of root elongation, as well as Al contents in root tips as parameters. Significant correlations between Al‐induced callose formation and Al contents in root tips (r² = 0.64**) and inhibition of root elongation (r² = 0.80***) were found. Excised root tips did not show a significant Al‐induced inhibition of root elongation. While average Al‐induced callose formation was similar for root tips of intact plants and excised root tips, mean Al contents in excised root tips were up to 1.5‐fold higher than in root tips of intact plants after 24 h of Al treatment. Aluminum‐induced callose formation as found in excised root tips did neither correspond to Al‐induced callose formation nor to inhibition of root elongation of intact plants. The addition of 10 mM glucose to the incubation medium led to a significant increase in the elongation of excised root tips and a 2‐3‐fold increase in Al‐induced callose formation. Staining with triphenyl‐tetrazolium‐chloride (TTC) revealed increased viability of these root segments. However, these effects of glucose supply did not improve the characterization of the cultivars for Al resistance. The results presented suggest that Al exclusion mechanisms expressed in root tips of intact plants might be non‐operational in excised root tips. Therefore, the characterization of maize germplasm for Al resistance using excised root tips appears not to be reliable.     

Varietal differences in the growth of rice plants in response to aluminum and silicon

Effects of Al (0–100 μM) and Si (0–2,000 μM) supplied singly or in combination on root growth of different rice varieties were examined under hydroponic conditions. Al addition inhibited root elongation of rice plants, and the inhibition increased with increasing amount of Al in the culture solution. Among 22 indica varieties and among 8 japonica varieties tested, IAC3 and Nakateshinsenbon were relatively tolerant to AI, respectively, whereas IR45 and Norinl were relatively sensitive to AI, respectively. Si exerted a beneficial effect at all levels of Si treatment on indica varieties, whereas Si supply resulted in a slight increase in the root dry weight of japonica varieties only at the highest level (2,000 μM Silo The alleviation of Al inhibition of rice root growth by Si was observed in the combination of Al and Si treatments. Alleviation was more pronounced for all the Si treatments in indica varieties than in japonica varieties, and the alleviation was maximum with 2,000 μM Si in IR45. The alleviation effect by Si was more pronounced in the AI-sensitive varieties than in the AI-tolerant varieties. The application of Si resulted in an increase in the contents of Al and Si in plants, and there was no relationship between the Al content and Al inhibition in plants.     

The significance of organic‐anion exudation for the aluminum resistance of primary triticale derived from wheat and rye parents differing in aluminum resistance

Eight primary octoploid triticale genotypes (xTriticosecale Wittmack) derived from four wheat cultivars (Triticum aestivum L.) and two rye inbred lines (Secale cereale L.) differing in aluminum (Al) resistance were investigated with respect to their response to Al supply. Aluminum‐induced inhibition of root elongation (48 h, 25 µM Al supply), callose formation, and the accumulation of Al in root tips (4 h, 25 µM Al supply) were used as parameters to assess Al resistance. Using these parameters, the existing information on Al resistance of the wheat and rye cultivars was generally confirmed. The triticale cultivars showed a wide range of Al resistance amongst the Al‐sensitive wheat and the Al‐resistant rye cultivars. The rye parents and the Al‐resistant wheat parent Carazinho were characterized by Al‐induced exudation particularly of citrate but also of malate from whole root systems of 14 d old seedlings (8 h, 50 µM Al supply). Regression analysis revealed that the degree of Al resistance of the triticale genotypes was closely related to the Al‐induced citrate exudation, which was mainly controlled by the Al resistance of the wheat parent.