Genetic manipulation in vesicular-arbuscular mycorrhizal fungi

The symbiosis between vesicular-arbuscular mycorrhizal (VAM) fungi and host plants develops after successful interactions between both partners. These interactions probably involve signal molecules produced by the host plant, by the fungi, or by both. So far the biotrophic status of VAM fungi has hampered the understanding of the processes regulating their physiology. However, among different methods for co-cultivating VAM fungi, root organ cultures (ROC) appear to be a useful technique for studying VAM development. This system has been useful in defining the nutritional requirements of VAM fungi in the precolonization stage and in obtaining axenic fungal material in various developmental stages. The work discussed here focuses on the application of Polymerase Chain Reaction (PCR) technology and the potential of promoting hyphal growth in the absence of the plant. These techniques are being used to study VAM fungi in two main areas. The first concerns the determination of the DNA sequences coding for the SSU ribosomal RNA of two VAM fungi. This approach has allowed the design of specific primers for the rapid identification and quantification of VAM fungi. The second area of research concerns the potential use of PCR technology to study selective expression of specific genes during fungal spore development in defined in vitro conditions. The achievement of this future prospect depends on the ability to prepare PCR-based cDNA libraries from small amounts of fungal material after stimulation of hyphal growth with CO₂ and plant flavonols.     

福建漳州常见药用植物根围的丛枝菌根真菌

为了解闽南地区药用植物根围丛枝菌根真菌多样性分布,作者调查了福建省漳州市20种常见药用植物根围的AM真菌。从福建省漳州市小溪镇、国强乡等地共分离出无梗囊霉属Acaulospora 12种、原囊霉属Archaeospora 1种、巨孢囊霉属Gigaspora 2种、球囊霉属Glomus 42种、盾巨孢囊霉属Scutellospora 9种,其中沙生球囊霉Glomus arenarium、金黄球囊霉Glomus aureum和厚皮球囊霉Glomus callosum等3种为我国新记录种。     

Intrasporal variability of ribosomal sequences in the endomycorrhizal fungus Gigaspora margarita

The sequence variability of the ribosomal internal transcribed spacer (ITS) region, which comprises the 5.8 gene and the flanking regions ITS1 and ITS2, was investigated in the arbuscular mycorrhizal fungus Gigaspora margarita. DNA analysis of a multispore preparation and three single spores led to the identification of 11 slightly different sequences (three variants within a single spore), indicating substantial intersporal and intrasporal genetic variability (up to 9% sequence divergence). The sequence variations inside a single spore may be higher than that observed between spores. Even so, primers designed on the ITS1 and ITS2 regions identified Gi. margarita isolates and detected the endophyte during colonization.     

Effects of mycorrhizal fungus isolates on mineral acquisition by Panicum virgatum in acidic soil

 Plant ability to withstand acidic soil mineral deficiencies and toxicities can be enhanced by root-arbuscular mycorrhizal fungus (AMF) symbioses. The AMF benefits to plants may be attributed to enhanced plant acquisition of mineral nutrients essential to plant growth and restricted acquisition of toxic elements. Switchgrass (Panicum virgatum L.) was grown in pH_Ca (soil:10 mM CaCl₂, 1 : 1) 4 and 5 soil (Typic Hapludult) inoculated with Glomus clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigaspora albida, Gi. margarita, Gi. rosea, and Acaulospora morrowiae to determine differences among AMF isolates for mineral acquisition. Shoots of mycorrhizal (AM) plants had 6.2-fold P concentration differences when grown in pH_Ca 4 soil and 2.9-fold in pH_Ca 5 soil. Acquisition trends for the other mineral nutrients essential for plant growth were similar for AM plants grown in pH_Ca 4 and 5 soil, and differences among AMF isolates were generally higher for plants grown in pH_Ca 4 than in pH_Ca 5 soil. Both declines and increases in shoot concentrations of N, S, K, Ca, Mg, Zn, Cu, and Mn relative to nonmycorrhizal (nonAM) plants were noted for many AM plants. Differences among AM plants for N and Mg concentrations were relatively small (<2-fold) and were large (2- to 9-fold) for the other minerals. Shoot concentrations of mineral nutrients did not relate well to dry matter produced or to percentage root colonization. Except for Mn and one AMF isolate, shoot concentrations of Mn, Fe, B, and Al in AM plants were lower than in nonAM plants, and differences among AM plants for these minerals ranged from a low of 1.8-fold for Fe to as high as 6.9-fold for Mn. Some AMF isolates were effective in overcoming acidic soil mineral deficiency and toxicity problems that commonly occur with plants grown in acidic soil. Accepted: 14 June 1999     

Ultrastructural localization of N-acetylglucosamine residues in the cell wall of Gigaspora margarita throughout its life-cycle

The cell ultrastructure of the VAM fungus Gigaspora margarita was examined, and its N-acetylglucosamine content and distribution were assessed by means of WGA/ovomucoid-gold labelling. The various ontogenic stages of the fungus were studied with particular reference to cell walls. The results provide new information on chitin incorporation during spore wall development. A decrease of chitin was observed which was correlated to the structural simplification of the fungus wall throughout its life-cycle. This suggests an involvement of chitin in specific biological functions such as mechanical resistance and plasticity.     

新疆北部地区常见植物根围的丛枝菌根真菌

从新疆北部地区24种常见植物根围土壤中分离并鉴定出5属27种丛枝菌根真菌,其中球囊霉属Glomus15种,无梗囊霉属Acaulospora9种,原囊霉属Archaeospora1种,内养囊霉属Entrophospora1种,巨孢囊霉属Gigaspora1种。道氏球囊霉Glomusdominikii是新记录种。