铝毒胁迫诱导菜豆柠檬酸的分泌与累积

水培试验结果表明 ,铝毒诱导菜豆柠檬酸的分泌与累积存在着显著的基因型差异 .Al3 + 浓度 <5 0 μmol·L-1时 ,柠檬酸分泌量随Al3 + 浓度的增大而增加 ;Al3 + 浓度在 5 0～ 80 μmol·L-1时 ,柠檬酸分泌量随Al3 + 浓度的增大而减小 .不同菜豆基因型以G1984 2的柠檬酸分泌量最大 ,单位干重Al吸收量最小 .铝毒胁迫时 ,不同菜豆基因型叶片柠檬酸累积量无明显差异 ,根系柠檬酸累积量为G1984 2 >AFR >ZPV >G5 2 73.菜豆柠檬酸分泌量缺P处理 <铝毒胁迫 ,5 0 μmol·L-1LaCl3 不能诱导菜豆分泌柠檬酸 ,表明柠檬酸的分泌与累积是菜豆抗铝毒胁迫的重要生理反应     

铝胁迫下黑麦和小麦根尖分泌有机酸的研究

通过建立的活体根培养及微量根尖分泌物收集系统,对铝胁迫下黑麦和小麦根尖分泌的有机酸进行研究。结果表明:50、100、200、300μmol·L-1 AlCl3处理后黑麦根尖分泌柠檬酸和苹果酸,而铝仅诱导小麦根尖分泌苹果酸。铝处理3h后,根尖分泌的苹果酸显著增加,并在9h内维持较高的分泌速率。铝诱导黑麦根尖分泌柠檬酸有明显的迟缓期,Al(300μmol·L-1)处理后的最初3h,根尖分泌的柠檬酸并不显著增加。在铝溶液中添加的阴离子通道抑制剂A-9-C(20、60、100μmol·L-1)显著抑制根尖分泌有机酸。然而,将黑麦根尖浸泡于含异三聚体G蛋白激活剂霍乱毒素(50ng·mL-1)后,根尖分泌的有机酸显著增加。说明建立的微量根尖分泌物收集系统适合于铝诱导根尖分泌有机酸的研究,小麦和黑麦根尖在铝胁迫下以不同模式通过阴离子通道分泌有机酸,而异三聚体G蛋白可能介导根尖分泌有机酸。     

耐铝的和对铝敏感的玉米自交系根系的有机酸分泌

对玉米不同耐铝自交系在含A1^3 (0.1mmol/L)的完全营养液和A1C13 14．3μmol/L CaCl2 227．5μmol/L溶液等两种溶液中根系有机酸的分泌特征进行了研究。铝胁迫下,耐铝自交系Z1的生长与正常偏离不大,表现出较强的耐铝性,而铝敏感自交系Z2的生长则受到明显抑制。2种自交系根系分泌的有机酸种类包括苹果酸、柠檬酸、琥珀酸、马米酸、乙酸和草酸等,以苹果酸为主;其分泌量随铝处理时间而异。在两种溶液中,铝胁迫均可显著增加Z1苹果酸分泌量,且根系内苹果酸含量也显著增加。铝胁迫下,Z1根系NADP—苹果酸脱氢酶活性显著增加。从对试验结果分析得出：根系分泌苹果酸可能是玉米耐铝自交系适应酸性土壤逆境的生理特性之一,而分泌的苹果酸可能是在根系中通过PEP→4OAA→苹果酸途径合成的。     

黑麦对难溶性磷酸盐的吸收及活化机制研究

以2个黑麦品种冬牧70和King为材料,研究了植物对难溶性磷酸盐的吸收及活化,以揭示植物抵御酸性土壤逆境的机制.结果显示,(1)在活性铝含量高的赤红壤中施用磷酸铝、磷酸铁、磷酸钙等难溶性磷酸盐后,植株的生物产量和磷的积累量分别增加了0.84~6.38倍和0.60~20.5倍,且施用难溶性磷酸盐后冬牧70的生物产量和磷的积累量的增加量明显高于King.(2)铝胁迫下2种黑麦根系分泌物中的阴离子组分均能溶解难溶性磷酸盐,而在中性或阳离子组分中的难溶性磷酸盐溶解不显著;HPLC图谱显示,阴离子组分中含有柠檬酸和苹果酸.(3)铝胁迫下根系有机酸分泌量随铝处理浓度(10、30、50μmol/L AlCl3)的增加而增加,而且在柠檬酸或苹果酸溶液中难溶性磷酸盐的溶解度显著增加,其溶解的磷随有机酸浓度的增加而增加.(4)黑麦冬牧70品种对难溶性磷酸盐的吸收、阴离子组分对难溶性磷酸盐的溶解及有机酸分泌作用均较King强.结果表明,在铝胁迫下根系分泌的有机酸是黑麦活化、吸收土壤中难溶性磷的有效机制.     

低磷胁迫下AM真菌对枳实生苗吸磷效应及根系分泌有机酸的影响

在温室沙培灭菌条件下,以Al-P为磷源、枳为试材、Glomus mosseae (G.m)和G.versiforme (G.v)为菌剂,研究低磷胁迫下AM真菌对枳实生苗干物重、吸磷效应及根系分泌有机酸的影响。结果表明,接种AM真菌显著增加枳地上部、地下部干物重,增幅16.79%~135.25%;同时显著增加其吸磷量,菌丝对植株的吸磷贡献率为17.04%~71.95%(G.m>G.v),施Al-P显著提高菌丝吸磷贡献率。接种AM真菌的根系分泌的有机酸种类与对照有所不同,未接种处理枳分泌的有机酸有草酸、苹果酸、乳酸、乙酸、顺丁烯二酸和柠檬酸等6种,而接种G.m的则检测到草酸、酒石酸、苹果酸、乳酸、乙酸、柠檬酸、丁二酸等7种,G.v处理的检测到酒石酸,接种处理均未检测到顺丁烯二酸;接种丛枝菌根真菌增加了枳根系分泌有机酸的量(比未接种处理增加19.80~56.87 mg/kg,且施用AlPO₄后有机酸含量显著增加(增加20.06~21.84 mg/kg);未接种植株根系仅分泌少量有机酸;接种植株根系分泌的有机酸以苹果酸(42.87%)、柠檬酸(39.22%)和草酸(12.06%)为主。     

缺磷对不同基因型玉米根系分泌有机酸以及活化难溶性磷的影响

缺磷条件下水培６个基因型玉米杂交种以及它们的７个亲本,根系分泌液的ｐＨ较低,自交系更低,杂交种各基因型玉米分泌的有机酸以草酸为主,还有苹果酸等。缺磷处理的玉米根系分泌草酸量比供磷处理的高,其中铁单４,白单９和白单１３在缺磷时的草酸分泌量分别比供磷增加３．４,２．８和１．６倍,单交种白单９根系分泌物活化磷的能力最高。     

富钾基因型籽粒苋主要根系分泌物及其对土壤矿物态钾的活化作用

通过试验,研究了2种供K水平对籽粒苋(Amaranthus spp.)富K基因型和一般基因型根系分泌物含量变化的影响,以及在低K胁迫时3个生长期两类基因型主要根系分泌物含量的变化特点,模拟了籽粒苋根系分泌物对土壤矿物态钾的活化作用.结果表明,籽粒苋根系分泌物中可溶性糖、氨基酸和有机酸含量随供K水平的升高而降低,且富K基因型根系分泌物中3种物质的分泌量始终大于一般基因型;在正常供K条件下,两基因型根系分泌能力相近,但在低K处理时,前者显著高于后者,差异显著;在2种供K水平下,根系有机酸分泌量在3种分泌物中占绝对优势,分别是可溶性糖和氨基酸分泌量的几十倍和几百倍.籽粒苋生长到50 d时,一般基因型根系可溶性糖、氨基酸和有机酸的分泌量较40 d时迅速降低.富K基因型根系分泌物中可溶性糖、氨基酸和有机酸含量在3个生长时期均大于一般基因型,且随着生长时间的延长,两基因型间可溶性糖、氨基酸和有机酸含量的差异明显增大.两类基因型在3个生长时期均以分泌有机酸为主,其占总分泌量的93%以上.籽粒苋根系分泌物处理后的土壤速效钾含量均高于清水对照处理,富K基因型在低K胁迫时的根系分泌物对土壤K的活化作用明显大于一般基因型.     

铝胁迫下植物根系的有机酸分泌及其解毒机理

酸性土壤中的铝毒害问题,已成为限制植物生长发育的主要因素之一.耐铝植物通过根系分泌有机酸来解除或减轻铝的毒害是外部解铝毒的重要机制.文章对铝胁迫下植物根系分泌有机酸的种类,有机酸解铝毒机理、解铝毒能力,有机酸分泌方式及调控其分泌的主要因素等相关研究进行综述.     

缺磷对不同基因型玉米根系分泌有机酸以及活化难溶性磷的影响(简报)

缺磷条件下水培６个基因型玉米杂交种以及它们的７个亲本,根系分泌液的ｐＨ较低,自交系更低;杂交种各基因型玉米分泌的有机酸以草酸为主,还有苹果酸等。缺磷处理的玉米根系分泌草酸量比供磷处理的高．其中铁单４、白单９和白单１３在缺磷时的草酸分泌量分别比供磷增加３．４、２．８和１．６倍。单交种白单９根系分泌物活化磷的能力最高。     

缺磷白羽扇豆排根与非排根区根尖分泌有机酸的比较

采用根系分泌有机酸原位收集方法及市郊液相色谱技术分析了供磷及缺磷后不同时间白羽扇豆（Ｌｕｐｉｎｕｓ ａｉｂｕｓ Ｌ．）非排根区根尖和排根分泌有机酸的种类和数量,以及相应的根尖、排根组织,茎木质部、韧皮部汁液中有机酸含量的变化。结果表明：⑴缺磷能够诱导白羽扇豆要系产生大量排根,根系的有机酸分泌量也明显增加。⑵无论在供磷或缺磷条件下,排根与非排根区根区根尖组织中的有机酸种类相同,但排根主要分泌柠檬酸和     

Response of rice to Al stress and identification of quantitative trait Loci for Al tolerance

Rice (Oryza sativa L.) shows the highest tolerance to Al toxicity among small-grain cereal crops, however, the mechanisms and genetics responsible for its high Al tolerance are not yet well understood. We investigated the response of rice to Al stress using the japonica variety Koshihikari in comparison to the indica variety Kasalath. Koshihikari showed higher tolerance at various Al concentrations than Kasalath. The Al content in root apexes was less in Koshihikari than in Kasalath, suggesting that exclusion mechanisms rather than internal detoxification are acting in Koshihikari. Al-induced secretion of citrate was observed in both Koshihikari and Kasalath, however, it is unlikely to be the mechanism for Al tolerance because there was no significant difference in the amount of citrate secreted between Koshihikari and Kasalath. Quantitative trait loci (QTLs) for Al tolerance were mapped in a population of 183 backcross inbred lines (BILs) derived from a cross of Koshihikari and Kasalath. Three putative QTLs controlling Al tolerance were detected on chromosomes 1, 2 and 6. Kasalath QTL alleles on chromosome 1 and 2 reduced Al tolerance but increased tolerance on chromosome 6. The three QTLs explained about 27% of the phenotypic variation in Al tolerance. The existence of QTLs for Al tolerance was confirmed in substitution lines for corresponding chromosomal segments.     

The combined treatment of Mn and Al alleviates the toxicity of Al or Mn stress alone in barley

Aluminum (Al) and manganese (Mn) toxicity commonly coexists in acid soil, so the crop cultivars suitable for planting in acid soil should show high tolerance to both elements simultaneously. However, it is still not clear if the toxicity of Mn and Al on plant growth is antagonistic or synergistic, and the plants with Al tolerance are also tolerant to Mn toxicity. In this study, three barley genotypes (one Tibetan wild and two cultivated), differing in Al tolerance, were characterized for growth and physiological responses to Al or Mn toxicity as well as the combined treatment of the two toxic elements. Interestingly, it has been found that the combined treatment of both metals was less affected in comparison with Al or Mn treatment alone, in terms of plant growth, Al or Mn concentration in plant tissues, and photosynthetic parameters, indicating antagonistic interaction of Al and Mn for their effect on plant growth and physiological traits. The results also showed that there was a dramatic difference among barley genotypes in Mn toxicity tolerance and XZ16 showed much higher tolerance than other two genotypes. High Mn tolerance is mainly described to less Mn uptake and lower Mn concentration in plants, and Mn tolerance is independent of Al tolerance.     

Identification and characterization of aluminum tolerance loci in Arabidopsis (Landsberg erecta x Columbia) by quantitative trait locus mapping. A physiologically simple but genetically complex trait

Aluminum (Al) toxicity, which is caused by the solubilization of Al3+ in acid soils resulting in inhibition of root growth and nutrient/water acquisition, is a serious limitation to crop production, because up to one-half of the world's potentially arable land is acidic. To date, however, no Al tolerance genes have yet been cloned. The physiological mechanisms of tolerance are somewhat better understood; the major documented mechanism involves the Al-activated release of Al-binding organic acids from the root tip, preventing uptake into the primary site of toxicity. In this study, a quantitative trait loci analysis of Al tolerance in Arabidopsis was conducted, which also correlated Al tolerance quantitative trait locus (QTL) with physiological mechanisms of tolerance. The analysis identified two major loci, which explain approximately 40% of the variance in Al tolerance observed among recombinant inbred lines derived from Landsberg erecta (sensitive) and Columbia (tolerant). We characterized the mechanism by which tolerance is achieved, and we found that the two QTL cosegregate with an Al-activated release of malate from Arabidopsis roots. Although only two of the QTL have been identified, malate release explains nearly all (95%) of the variation in Al tolerance in this population. Al tolerance in Landsberg erecta x Columbia is more complex genetically than physiologically, in that a number of genes underlie a single physiological mechanism involving root malate release. These findings have set the stage for the subsequent cloning of the genes responsible for the Al tolerance QTL, and a genomics-based cloning strategy and initial progress on this are also discussed.     

Bacterial citrate synthase expression and soil aluminum tolerance in transgenic alfalfa

Alfalfa is very sensitive to soil acidity and its yield and stand duration are compromised due to inhibited root growth and reduced nitrogen fixation caused by Al toxicity. Soil improvement by liming is expensive and only partially effective, and conventional plant breeding for Al tolerance has had limited success. Because tobacco and papaya plants overexpressing Pseudomonas aeruginosa citrate synthase (CS) have been reported to exhibit enhanced tolerance to Al, alfalfa was engineered by introducing the CS gene controlled by the Arabidopsis Act2 constitutive promoter or the tobacco RB7 root-specific promoter. Fifteen transgenic plants were assayed for exclusion of Al from the root tip, for internal citrate content, for growth in in vitro assays, or for shoot and root growth in either hydroponics or in soil assays. Overall, only the soil assays yielded consistent results. Based on the soil assays, two transgenic events were identified that were more aluminum-tolerant than the non-transgenic control, confirming that citrate synthase overexpression can be a useful tool to help achieve aluminum tolerance. Pierluigi Barone and Daniele Rosellini contributed equally to this work.     

Aluminum tolerance in maize is correlated with increased levels of mineral nutrients, carbohydrates and proline, and decreased levels of lipid peroxidation and Al accumulation

We investigated the uptake of aluminum (Al) and transport to shoots in two inbred maize lines (Zea mays L., VA-22 and A(4/67)) differing in Al tolerance. Seedlings were grown for 7 days in hydroponic culture with nutrient solution that contained 0, 240, 360, and 480muM Al at pH 4.2. After 7 days of exposure to Al, roots of sensitive maize line (A(4/67)) plants accumulated 2-2.5 times more Al than roots of tolerant line (VA-22) plants. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the tolerant line retained higher concentrations of Ca(2+), Mg(2+), and K(+) compared with the sensitive line. In response to Al treatment, proline (Pro) concentration increased three-fold in roots of tolerant plants, while a slight increase was observed in roots of sensitive-line plants. A substantial carbon surplus (two-fold increase) was observed in roots of the Al-tolerant maize line. Carbohydrate concentration remained almost unchanged in roots of Al-sensitive line plants. Al treatment triggered the enhancement of lipid peroxidation in the sensitive line, while no change in lipid peroxidation level was observed in the tolerant maize line. These data provide further support to the hypothesis that a mechanism exists that excludes Al from the roots of the tolerant maize line, as well as an internal mechanism of tolerance that minimizes accumulation of lipid peroxides through a higher Pro and carbohydrate content related to osmoregulation and membrane stabilization.     

Genetic architecture of aluminum tolerance in rice (Oryza sativa) determined through genome-wide association analysis and QTL mapping

Aluminum (Al) toxicity is a primary limitation to crop productivity on acid soils, and rice has been demonstrated to be significantly more Al tolerant than other cereal crops. However, the mechanisms of rice Al tolerance are largely unknown, and no genes underlying natural variation have been reported. We screened 383 diverse rice accessions, conducted a genome-wide association (GWA) study, and conducted QTL mapping in two bi-parental populations using three estimates of Al tolerance based on root growth. Subpopulation structure explained 57% of the phenotypic variation, and the mean Al tolerance in Japonica was twice that of Indica. Forty-eight regions associated with Al tolerance were identified by GWA analysis, most of which were subpopulation-specific. Four of these regions co-localized with a priori candidate genes, and two highly significant regions co-localized with previously identified QTLs. Three regions corresponding to induced Al-sensitive rice mutants (ART1, STAR2, Nrat1) were identified through bi-parental QTL mapping or GWA to be involved in natural variation for Al tolerance. Haplotype analysis around the Nrat1 gene identified susceptible and tolerant haplotypes explaining 40% of the Al tolerance variation within the aus subpopulation, and sequence analysis of Nrat1 identified a trio of non-synonymous mutations predictive of Al sensitivity in our diversity panel. GWA analysis discovered more phenotype-genotype associations and provided higher resolution, but QTL mapping identified critical rare and/or subpopulation-specific alleles not detected by GWA analysis. Mapping using Indica/Japonica populations identified QTLs associated with transgressive variation where alleles from a susceptible aus or indica parent enhanced Al tolerance in a tolerant Japonica background. This work supports the hypothesis that selectively introgressing alleles across subpopulations is an efficient approach for trait enhancement in plant breeding programs and demonstrates the fundamental importance of subpopulation in interpreting and manipulating the genetics of complex traits in rice.     

Phosphorus and aluminum interactions in soybean in relation to aluminum tolerance. Exudation of specific organic acids from different regions of the intact root system

Aluminum (Al) toxicity and phosphorus (P) deficiency often coexist in acid soils that severely limit crop growth and production, including soybean (Glycine max). Understanding the physiological mechanisms relating to plant Al and P interactions should help facilitate the development of more Al-tolerant and/or P-efficient crops. In this study, both homogeneous and heterogeneous nutrient solution experiments were conducted to study the effects of Al and P interactions on soybean root growth and root organic acid exudation. In the homogenous solution experiments with a uniform Al and P distribution in the bulk solution, P addition significantly increased Al tolerance in four soybean genotypes differing in P efficiency. The two P-efficient genotypes appeared to be more Al tolerant than the two P-inefficient genotypes under these high-P conditions. Analysis of root exudates indicated Al toxicity induced citrate exudation, P deficiency triggered oxalate exudation, and malate release was induced by both treatments. To more closely mimic low-P acid soils where P deficiency and Al toxicity are often much greater in the lower soil horizons, a divided root chamber/nutrient solution approach was employed to impose elevated P conditions in the simulated upper soil horizon, and Al toxicity/P deficiency in the lower horizon. Under these conditions, we found that the two P-efficient genotypes were more Al tolerant during the early stages of the experiment than the P-inefficient lines. Although the same three organic acids were exuded by roots in the divided chamber experiments, their exudation patterns were different from those in the homogeneous solution system. The two P-efficient genotypes secreted more malate from the taproot tip, suggesting that improved P nutrition may enhance exudation of organic acids in the root regions dealing with the greatest Al toxicity, thus enhancing Al tolerance. These findings demonstrate that P efficiency may play a role in Al tolerance in soybean. Phosphorus-efficient genotypes may be able to enhance Al tolerance not only through direct Al-P interactions but also through indirect interactions associated with stimulated exudation of different Al-chelating organic acids in specific roots and root regions.     

Comparative mapping of a major aluminum tolerance gene in sorghum and other species in the poaceae

In several crop species within the Triticeae tribe of the grass family Poaceae, single major aluminum (Al) tolerance genes have been identified that effectively mitigate Al toxicity, a major abiotic constraint to crop production on acidic soils. However, the trait is quantitatively inherited in species within other tribes, and the possible ancestral relationships between major Al tolerance genes and QTL in the grasses remain unresolved. To help establish these relationships, we conducted a molecular genetic analysis of Al tolerance in sorghum and integrated our findings with those from previous studies performed in crop species belonging to different grass tribes. A single locus, AltSB, was found to control Al tolerance in two highly Al tolerant sorghum cultivars. Significant macrosynteny between sorghum and the Triticeae was observed for molecular markers closely linked to putatively orthologous Al tolerance loci present in the group 4 chromosomes of wheat, barley, and rye. However, AltSB was not located within the homeologous region of sorghum but rather mapped near the end of sorghum chromosome 3. Thus, AltSB not only is the first major Al tolerance gene mapped in a grass species that does not belong to the Triticeae, but also appears to be different from the major Al tolerance locus in the Triticeae. Intertribe map comparisons suggest that a major Al tolerance QTL on rice chromosome 1 is likely to be orthologous to AltSB, whereas another rice QTL on chromosome 3 is likely to correspond to the Triticeae group 4 Al tolerance locus. Therefore, this study demonstrates a clear evolutionary link between genes and QTL encoding the same trait in distantly related species within a single plant family.