根系分泌物研究方法(综述)

根系分泌物是植物与土壤进行物质、能量与信息交流的重要载体物质.研究根系分泌物的种类、数量对了解植物与土壤及根际微生物相互作用机理具有重要指导意义,根系分泌物研究方法的选择对研究结果有重要的影响.本文着重讨论根系分泌物收集、分离纯化及鉴定的常用方法,并列举特定根系分泌物的研究方法,旨在为根系分泌物的研究提供借鉴和参考.     

Rhizobium tropiciteu genes involved in specific uptake of Phaseolus vulgaris bean-exudate compounds

Rhizobium tropici nodulates and fixes nitrogen in bean. In the R. tropici strain CFN299 we identified and characterized teu genes (tropiciexudate uptake) induced by bean root exudates, localized by insertion of a promoter-less Tn5-gusA1 transposon. teu genes are present on a plasmid of around 185 kb that is conserved in all R. tropici strains. Proteins encoded by teu genes show similarity to ABC transporters, specifically to ribose transport proteins. No induction of the teu genes was obtained by treatment with root exudates from any of several other plants tested, with the exception of Macroptilium atropurpureum, which is also a host plant for R. tropici. It appears that the inducing compound is characteristic of bean and closely related legumes. It is present in root exudates, but not in seeds. This compound is removed, presumably by metabolism, from the exudates by the majority of bean-nodulating rhizobia (such as R. etli, R. leguminosarum bv. phaseoli and R.␣giardinii). The principal inducing compound has not been identified, but some induction was obtained using trigonelline. The CFN299 strain seems to have an additional uptake system, as no phenotype is observed in two different mutants. R. tropici strain CIAT899, on the other hand, must have only one uptake system, since a mutant bearing an insertion in the teu genes could not remove the compound from the exudates as efficiently as the wild type, and it showed diminished nodulation competitiveness. Received: 21 November 1997 / Accepted: 18 March 1998     

模拟根系分泌物输入对高寒退化草地土壤微生物残体的影响

微生物残体是稳定土壤碳库的重要来源，对退化生境碳的固持和积累具有重要意义。植物根系分泌物作为植物-土壤-微生物"交流"的媒介，是调控土壤微生物残体迁移转化的关键。因此，以极度退化草地土壤为对象，以氨基糖为标志物，模拟研究了不同氮浓度（低氮-LN：0.1 gN/kg；高氮-HN：0.2 gN/kg）和多样性（3种化合物、9种化合物）根系分泌物输入对土壤微生物残体的影响。结果表明：（1）根系分泌物输入可显著增加高寒退化草地土壤微生物残体含量，且主要由真菌残体贡献。其中高氮和低多样性处理增加最明显，微生物残体和真菌残体分别增加了101.14%，125.16%，而低氮和高多样性处理微生物残体和真菌残体仅增加了35.79%，33.51%。（2）根系分泌物的输入可增加土壤β-葡萄糖苷酶、土壤磷酸酶和过氧化物酶活性，促进微生物的生长，而降低β-N-乙酰氨基葡萄糖苷酶活性，减少微生物残体的分解。（3）回归分析结果显示，土壤微生物残体与土壤环境的C/N呈显著负相关，与微生物生物量C/N呈显著正相关。上述结果表明，在未来退化草地恢复中，可充分利用模拟根系分泌物输入的土壤固碳策略，即通过提高土壤氮的有效性，促进微生物的生长，加快代谢周转，进一步提高微生物残体含量。     

Root exudates from sunflower (Helianthus annuus L.) show a strong adsorption ability toward Cd(II)

Abstract

Cd(II) adsorption of root exudates from sunflower (Helianthus annuus L.) seedling was investigated by Cd ion-selective electrode, Fourier Transform Infrared spectroscopy, and fluorescence spectroscopy. Root exudates from Helianthus annuus L. had strong adsorption ability toward Cd(II). The adsorption process was pH-dependent and the maximum adsorption capacity, 150.8 mg g^?1, was observed at pH 7.0. Root exudates had pK _a1 at 4.7 for carboxyl and pK _a2 at 9.2 for phenolic, and amino groups. The aliphatic and aromatic (C?H) groups, amide III group, and the C (=O)?O and sulfonate groups were responsible for Cd(II) adsorption. The excitation emission matrix fluorescence spectroscopy showed protein-like substances participated in Cd adsorption and formed strong complexes, with conditional stability constants of 4.70 and 4.32, which is a little lower than that determined by potentiometric methods, 5.13. The strong Cd complexing ability of root exudates implies that root exudates may significantly affect mobility, toxicity, and phytoavailability of Cd. Cd binding of root exudates may be attributed to its interaction with the proteins, polysaccharides, and phenolic compounds in root exudates.     

Hatch and Reproduction of Globodera tabacum tabacum in Response to Tobacco,Tomato, or Black Nightshade

The effects of broadleaf tobacco, tomato, and black nightshade on juvenile hatch and reproduction of Globodera tabacum tabacum were determined in laboratory and greenhouse experiments. Root exudates from nightshade stimulated greater egg hatch than those from either ''Rutgers'' tomato or ''86-4'' tobacco. Hatch was greater at higher proportions of root exudates for all three plant species. Root exudates from plants greater than 3 weeks old stimulated more hatch than younger plants. No regression relationships existed between plant age and nematode batch. In other experiments, hatch from eggs in cysts was higher for tomato and nightshade after 10 weeks in greenhouse pots compared to tobacco and bare soil. Numbers of second-stage juveniles in eggs in cysts produced from a previous generation on the same host were highest on nightshade and less on tomato and tobacco. Cysts of variable age recovered from field soil had increased hatch in both root exudates or water compared to recently produced cysts from plants in growth chambers. Globodera t. tabacum may be subject to both host and environmentally mediated diapause.     

Warming increases soil carbon input in a Sibiraea angustata-dominated alpine shrub ecosystem

Plant-derived carbon (C) inputs via foliar litter, root litter and root exudates are key drivers of soil organic C stocks. However, the responses of these three input pathways to climate warming have rarely been studied in alpine shrublands. By employing a 3-year warming experiment (increased by 1.3 °C), we investigated the effects of warming on the relative C contributions from foliar litter, root litter and root exudates from Sibiraea angustata, a dominant shrub species in an alpine shrubland on the eastern Qinghai-Tibetan Plateau. The soil organic C inputs from foliar litter, root litter and root exudates were 77.45, 90.58 and 26.94 g C m⁻², respectively. Warming only slightly increased the soil organic C inputs from foliar litter and root litter by 8.04 and 11.13 g C m⁻², but significantly increased the root exudate C input by 15.40 g C m⁻². Warming significantly increased the relative C contributions of root exudates to total C inputs by 4.6% but slightly decreased those of foliar litter and root litter by 2.5% and 2.1%, respectively. Our results highlight that climate warming may stimulate plant-derived C inputs into soils mainly through root exudates rather than litter in alpine shrublands on the Qinghai-Tibetan Plateau.     

The presence of heartwood decay,a precursor to hollow formation,within Eucalyptus camaldulensis in relation to stem size

River Red Gums (Eucalyptus camaldulensis Dehnh.) are large trees that dominated many of continental Australia's riparian areas, providing abundant hollows for nesting and denning fauna. Land clearing and forestry have reduced the availability of large trees, and much of the remaining forest is dominated by small regrowth trees that lack visible hollow entrances. Inspection of recently felled River Red Gums revealed that heartwood decay, a precursor of hollow formation, can be common in relatively small trees. Internal decay and voids remain inaccessible until stochastic damage exposes them, which may not occur until the tree is old, and hence probably large. This discrepancy indicates that there is likely to be a size range of trees into which artificial entrances can be added to quickly increase hollow availability in landscapes undergoing active restoration as fauna habitat.     

The gum exudates from Brachystegia and Julbernardia species

Analytical data are presented for the water-soluble gum exudates from Brachystegia glaucescens, B. spiciformis, and Julbernardia globiflora. They are acidic polysaccharides containing glucuronic acid, 4-O-methylglucuronic acid and galacturonic acid, together with galactose, minor amounts of arabinose, and relatively high proportions of rhamnose. The exudate from B. glaucescens is of particular interest in having high molecular weight, high intrinsic viscosity, and a high methoxyl content. The nitrogen content of all three gums is low, but amino acid analysis shows that proteinaceous components are involved, as in the gum exudates from other genera.     

Effects of aluminium treatment on Norway spruce roots: Aluminium binding forms,element distribution,and release of organic substances

In order to investigate if Al resistance in Norway spruce (Picea abies[L.] Karst.) can be attributed to similar exclusion mechanisms as they occur in several crop plants, three-year-old Norway spruce plants were treated for one week in hydroculture with either 500 μM AlCl₃ or CaCl₂ solutions at pH 4. Sequential root extraction with 1 M NH₄Cl and 0.01 M HCl and EDX microanalysis revealed that Al and Ca in cell walls and on the surface participated in exchange processes. About half of the Al extracted by the sequential extraction was not exchangeable by 1 M NH₄Cl. Phenolics and phosphate present in the root extracts are possible ligands for Al adsorbed to or precipitated at the root in a non-exchangeable form. In both treatments, C release during the first period of 2 d was much higher than during the remaining time of the experiment. Al treated plants released less total C, carbohydrates and phenolics than did Ca treated plants. Acetate was the only organic acid anion that could be detected in some samples of both treatments. Free amino acids were present at micromolar concentrations but as hydrolysis did not increase their yield, there was no evidence of peptide release. One to two thirds of the released C were large enough not to pass a 1 kDa ultrafilter. The results suggest that exudation of soluble organic complexors is not a major Al tolerance mechanism in Norway spruce, although complexation of Al by phenolic substances released by the root could be detected by fluorescence spectroscopy. Aluminium tolerance could rather be attributed to immobilization in the root apoplast, where strong binding sites are available or precipitation may occur. This revised version was published online in June 2006 with corrections to the Cover Date.