Spatial distribution of chitinases and β-1,3-glucanase transcripts in bean arbuscular mycorrhizal roots under low and high soil phosphate conditions

Arbuscular mycorrhizal (AM) fungi extensively colonize the root cortex under low-soil-phosphate (P) conditions, whereas infection is limited under high-P conditions. Fungal growth under both P conditions might be influenced by plant defence-related gene expression. In this study, we used in situ hybridization methods to compare the cellular localization of three defence-related mRNAs in non-infected bean roots and in relation to fungal infection units. In non-infected and infected roots, mRNAs encoding acidic and basic endochitinases were generally most abundant in the vascular cylinder. High-P-grown mycorrhizal roots showed localized accumulation of the acidic endochitinase mRNA in cortical cells containing arbuscules and in their immediate vicinity (one to five cell layers). The pattern of accumulation of the basic endochitinase mRNA was not affected by P or AM fungal infection. At the low P concentration, the β-1,3-glucanase mRNA accumulated predominantly in the vascular cylinder of non-infected roots. Suppression of β-1,3-glucanase mRNA accumulation in these tissues was observed in non-infected roots at the high-P and in mycorrhizal roots at both P concentrations. The observed suppression extends at least several mm from fungal infection units, characterizing a systemic effect. Beta-1,3-glucanase mRNA accumulated also around a number of cortical cells containing arbuscules only at the low P concentration. The localized accumulations of the endochitinase and β-1,3-glucanase mRNAs suggest that the encoded proteins might be involved in the control of intraradical fungal growth.     

The arbuscular mycorrhizal fungus, Glomus intraradices, induces the accumulation of cyclohexenone derivatives in tobacco roots

Tobacco (Nicotiana tabacum L.) plants were grown with and without the arbuscular mycorrhizal fungus, Glomus intraradices Schenk & Smith. High-performance liquid chromatographic analyses of methanolic extracts from mycorrhizal and non-mycorrhizal tobacco roots revealed marked fungus-induced changes in the patterns of UV-detectable products. The UV spectra of these products, obtained from an HPLC photodiode array detector, indicated the presence of several blumenol derivatives. The most predominant compound among these derivatives was spectroscopically identified as 13-hydroxyblumenol C 9-O-gentiobioside (“nicoblumin”), i.e. the 9-O-(6′-O-β-glucopyranosyl)-β-glucopyranoside of 13-hydroxy-6-(3-hydroxybutyl)-1,1,5-trimethyl-4-cyclohexen-3-one, a new natural product. This is the first report on the identification of blumenol derivatives in mycorrhizal roots of a non-gramineous plant. Received: 28 August 1998 / Accepted: 26 October 1998     

Root respiratory quotient and nitrate uptake in hydroponically grown non-mycorrhizal and mycorrhizal wheat

 Oxygen and CO₂ fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO₃ ^– uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at 4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O₂ consumption and NO₃ ^– uptake rates were similar and the CO₂ release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient (RQ, mol CO₂ mol^–1 O₂) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition per se. Accepted: 26 March 1999     

Mycorrhizal influence on protein and lipid of durum wheat grown at different soil phosphorus levels

 Root colonization by arbuscular mycorrhizal fungi (AMF) may affect protein and lipid composition of plants by altering P nutrition or by eliciting other metabolic responses in the host plant. This study was conducted to determine the effects of an AMF and soil P on seed protein and lipid contents and yield of two genotypes of durum wheat (Triticum durum L.). Plants were grown in a greenhouse using soil: sand mixes with different levels of P, and with or without the AMF Glomus mosseae [(Nicol. and Gerd.) Gerd. and Trappe]. Percentage AMF root colonization decreased as P added to soil increased. The wheat genotype CR057 had higher AMF root colonization but lower seed P and protein concentrations than CR006. Without added soil P, protein concentration was significantly lower and lipid concentration and seed dry weight higher in arbuscular mycorrhizal (AM) than in nonAM plants. Seed lipid and protein contents were highly correlated with P content of plants. In nonAM plants, seed lipid and protein contents were low with no added soil P and did not differ with added soil P. Seed protein/lipid (Pro/L) concentration ratios of AM plants were higher than those of nonAM plants only when no P was added to the soil. The data indicate different patterns of seed P accumulation and different relationships between seed P and protein and lipid in AM and nonAM plants. Thus, both the presence and degree of AMF root colonization affected seed lipid metabolism in these durum wheat genotypes. Accepted: 18 May 1999     

Chitin synthase genes in the arbuscular mycorrhizal fungus Glomus versiforme: full sequence of a gene encoding a class IV chitin synthase

Chitin synthase genes of the arbuscular mycorrhizal fungus Glomus versiforme were sought in an investigation of the molecular basis of fungal growth. Three DNA fragments (Gvchs1, Gvchs2 and Gvchs3) corresponding to the conserved regions of distinct chitin synthase (chs) genes were amplified by means of the polymerase chain reaction (PCR) with two sets of degenerate primers. Gvchs1 and Gvchs2 encode two class I chitin synthases, whereas Gvchs3 encodes a class IV chitin synthase. A genomic library was used to obtain the Gvchs3 complete gene (1194 amino acids), which shows a very close similarity to the class IV chitin synthase from Neurospora crassa.     

Litter N retention over winter for a low and a high phenolic species in the alpine tundra

Mycorrhizal fungus colonization of roots may modify plant metal acquisition and tolerance. In the present study, the contribution of the extraradical mycelium of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae (BEG 107), to the uptake of metal cations (Cu, Zn, Cd and Ni) by cucumber (Cucumis sativus) plants was determined. The influence of the amount of P supplied to the hyphae on the acquisition and partitioning of metal cations in the mycorrhizal plants was also investigated. Pots with three compartments were used to separate root and root-free hyphal growing zones. The shoot concentration of Cd and Ni was decreased in mycorrhizal plants compared to non-mycorrhizal plants. In contrast, shoot Zn and Cu concentrations were increased in mycorrhizal plants. High P supply to hyphae resulted in decreased root Cu concentrations and shoot Cd and Ni concentrations in mycorrhizal plants. These results confirm that some elements required for plant growth (P, Zn, Cu) are taken up by mycorrhizal hyphae and are then transported to the plants. Conversely, Cd and Ni were transported in much smaller amounts by hyphae to the plant, so that arbuscular mycorrhizal fungus colonization could partly protect plants from toxic effects of these elements. Selective uptake and transport of plant essential elements over non-essential elements by AM hyphae, increased growth of mycorrhizal plants, and metal accumulation in the root may all contribute to the successful growth of mycorrhizal plants on metal-rich substrates. These effects are stimulated when hyphae can access sufficient P in soil.     

Arbuscular mycorrhizal fungi can transfer substantial amounts of nitrogen to their host plant from organic material

Nitrogen (N) capture by arbuscular mycorrhizal (AM) fungi from organic material is a recently discovered phenomenon. This study investigated the ability of two Glomus species to transfer N from organic material to host plants and examined whether the ability to capture N is related to fungal hyphal growth. Experimental microcosms had two compartments; these contained either a single plant of Plantago lanceolata inoculated with Glomus hoi or Glomus intraradices, or a patch of dried shoot material labelled with (15)N and (13)carbon (C). In one treatment, hyphae, but not roots, were allowed access to the patch; in the other treatment, access by both hyphae and roots was prevented. When allowed, fungi proliferated in the patch and captured N but not C, although G. intraradices transferred more N than G. hoi to the plant. Plants colonized with G. intraradices had a higher concentration of N than controls. Up to one-third of the patch N was captured by the AM fungi and transferred to the plant, while c. 20% of plant N may have been patch derived. These findings indicate that uptake from organic N could be important in AM symbiosis for both plant and fungal partners and that some AM fungi may acquire inorganic N from organic sources.     

盐渍条件下AM真菌对大豆生长和离子含量的影响

盐渍条件下研究了丛枝菌根(AM)真菌对大豆Glycine max植株生长和叶片离子含量的影响。结果表明,接种摩西球囊霉Glomus mosseae处理的叶片K+含量和K/Na比显著高于对照,而Na+含量无显著差异。G.mosseae显著增加了大豆植株生长量,这一效应随盐处理浓度的提高而增大。表明盐渍条件下AM真菌提高大豆抗盐性与其增加K+吸收和运输有关。     

Interactions of Paecilomyces lilacinus strain 251 with the mycorrhizal fungus Glomus intraradices: Implications for Meloidogyne incognita control on tomato

The interactions of Paecilomyces lilacinus strain 251 with the arbuscular mycorrhizal fungus Glomus intraradices and their significance for the control of Meloidogyne incognita on tomato were investigated in greenhouse experiments. Application of P. lilacinus had no effect on the frequency and intensity of tomato root colonization by G. intraradices. Likewise, the decline of the nematophagous fungus densities after single application in soil was not affected by the presence of the mycorrhizal fungus. Single application of P. lilacinus, as pre-planting soil treatment, resulted in significant reduction of nematode damage. In contrast, mycorrhizal inoculation did not provide sufficient biocontrol. Combined application of the two agents did not enhance root protection compared to single treatments. Double treatment of mycorrhized seedlings with P. lilacinus, as seedling drench and pre-planting soil treatment, 4 and 1 week before transplanting, respectively, resulted in the highest reduction of the nematode damage. These results indicate the potential of the commercial P. lilacinus strain 251 and mycorrhiza for integration in nematode control strategies.