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     

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.     

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.     

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.     

Physiological adaptations to phosphorus deficiency during proteoid root development in white lupin

Release of large amounts of citric acid from specialized root clusters (proteoid roots) of phosphorus (P)-deficient white lupin (Lupinus albus L.) is an efficient strategy for chemical mobilization of sparingly available P sources in the rhizosphere. The present study demonstrates that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly restricted to mature root clusters in the later stages of P deficiency. Inhibition of citrate exudation by exogenous application of anion-channel blockers such as ethacrynic- and anthracene-9-carboxylic acids may indicate involvement of an anion channel. Phosphorus-deficiency-induced accumulation and subsequent exudation of citric acid seem to be a consequence of both increased biosynthesis and reduced metabolization of citric acid in the proteoid root tissue, indicated by increased in-vitro activity and enzyme protein levels of phosphoenolpyruvate carboxylase (EC 4.1.1.31), and reduced activity of aconitase (EC 4.2.1.3) and root respiration. Similar to citric acid, acid phosphatase, which is secreted by roots and involved in the mobilization of the organic soil P fraction, was released predominantly from proteoid roots of P-deficient plants. Also ³³Pi uptake per unit root fresh-weight was increased by approximately 50% in juvenile and mature proteoid root clusters compared to apical segments of non-proteoid roots. Kinetic studies revealed a K _m of 30.7 μM for Pi uptake of non-proteoid root apices in P-sufficient plants, versus K _m values of 8.5–8.6 μM for non-proteoid and juvenile proteoid roots under P-deficient conditions, suggesting the induction of a high-affinity Pi-uptake system. Obviously, P-deficiency-induced adaptations of white lupin, involved in P acquisition and mobilization of sparingly available P sources, are predominantly confined to proteoid roots, and moreover to distinct stages during proteoid root development. Received: 10 September 1998 / Accepted: 22 December 1998     

Quantification of endogenous gibberellins in exudates from fruits of Malus domestica

In exudates from developing apple fruits GA₁, GA₃, GA₄, GA₇, GA₂₀ and GA₃₄ could be identified and subsequently quantified by LC-ESI-MS selected-ion-monitoring analyses on the basis of internal standards. This is the first evidence obtained by mass spectrometrical analysis which demonstrates export of endogenous GAs from the fruits during the period when flower induction occurs. The observed differences in GA₄ export are discussed in connection with biennial bearing.     

Polymer and sprinkler droplet energy effects on sugar beet emergence, soil penetration resistance, and aggregate stability

The rapid development of agricultural biotechnology and release of new transgenic plants for agriculture has provided many economic benefits, but has also raised concern over the potential impact of transgenic plants on the environment. Considerable research has now been conducted on the effects of transgenic plants on soil microorganisms. These effects include unintentional changes in the chemical compositions of root exudates, and the direct effects of transgenic proteins on nontarget species of soil microorganisms. Most studies to date suggest that transgenic plants that have been released cause minor changes in microbial community structures that are often transient in duration. However, due to our limited knowledge of the linkage between microbial community structure and function, more work needs to be done on a case-by-case basis to further evaluate the effects of transgenic plants on soil microorganisms and soil ecosystem functions. This review summarizes the results of a variety of experiments that have been conducted to specifically test the effects of transgenic plants on soil microorganisms, and particularly examines the types of methods that are being used to study microbial interactions with transgenic plants.