Hydroxyproline-rich glycoprotein mRNA accumulation in maize root cells colonized by an arbuscular mycorrhizal fungus as revealed by in situ hybridization

Summary To determine whether the expression of cell wall related genes changes during the establishment of an arbuscular mycorrhizal symbiosis (AM), we studied the expression of a maize hydroxyproline-rich glycoprotein (HRGP) gene. In situ hybridization showed that, in differentiated cells of maize roots, mRNA accumulation corresponding to the gene encoding for HRGP was only found when the cells were colonized by the endomycorrhizal fungusGlomus versiforme.     

Growth and sporulation of the arbuscular mycorrhizal fungus Glomus caledonium in dual culture with transformed carrot roots

Glomus caledonium was established in a dual culture with Ri T-DNA-transformed carrot roots. A modification of the minimal M medium buffered at pH 6.50 with 10 mM MES and solidified with 0.4% unpurified gellan gum allowed spore germination and formation of the symbiosis, together with the development of an extensive extramatrical mycelium and sporulation. Spore production increased with culture generation and most spores were viable. These spores colonized carrot roots and completed the fungal life cycle. In many cultures, sporulation was accompanied by the formation of arbuscule-like structures on short and thickened lateral branches of main hyphae. Root colonization was of the Paris-type with hyphae spreading intracellularly. Most colonized root cells contained coils of thickened hyphae, sometimes surrounded by fine hyphae, but no typical arbuscules were observed. Accepted: 26 January 2000     

Growth and nitrogen fixation ofAzolla pinnata andAzolla caroliniana as affected by urea fertilizer and their influence on rice yield

Soils from avocado (Persea americana Mill.) orchards in Israel (IS) and California (CA), both sites with a Mediterranean climate, were sampled and analyzed for the species and quantities of vesicular-arbuscular mycorrhizal fungus (VAMF) spores in them, and for soil physical and chemical characteristics.Numbers of spores were similar in soil from IS and CA but the dominant VAMF species were very different. In IS the most common fungi were Sclerocystis sinuosa and Glomus macrocarpum. In CA, Gl. constrictum was present in every orchard examined and Gl. fasciculatum was nearly as widespread. Acaulospora spp. and other Glomus spp. also were found, including A. elegans which has never before been reported from CA.The differences in VAMF populations and species constituents found on two continents but in areas with similar climates and soil types may be due to host or edaphic factors. Different avocado rootstocks are used in the two countries and lower pH and higher soil fertility levels were present in CA soils.The total VAMF spore populations in each orchard was about 275 per 100 mL soil. The population level was not correlated with any of the soil physical or chemical characteristics examined nor with avocado cultivar or age. In IS no fungus spores were found in three orchards; available P, Ca, Mg and Cu levels were high in these soils.     

Stimulation of Growth and Nutrient Uptake by VAM Fungi in Brassica Oleracea Var. Capitata

Cabbage (Brassica oleracea, var. capitata, cv. Hercules) seedlings were inoculated with vesicular-arbuscular mycorrhizal (VAM) fungi Glomus fasciculatum, G. aggregatum, and G. mosseae. Differential efficiency in mycorrhizal colonization and the specificity of fungal symbiont to stimulate the growth and nutrient uptake of the host were observed. In addition, there was an increase in phenol, protein, reducing sugar contents, and peroxidase activity in the VAM inoculated seedlings. Since these compounds are known to confer resistance against fungal pathogens, the use of VAM as a biological control agent to protect cabbage against several root diseases is suggested.     

Soil color and surface residue effects on seedling light environment

Three leafless pea cultivars (JI 1198, BS 142 and BS 4) with the same phenotype and similar patterns of development, were tested in a sterilized low-phosphate soil for their response to phosphate fertilizer and to vesicular-arbuscular mycorrhizal (VAM) infection by threeGlomus species. Cultivar JI 1198 was very responsive to phosphate but not to inoculation withGlomus mosseae, Glomus caledonium orGlomus epigaeum. Phosphate and VAM treatments increased growth of cultivar BS 142 but were ineffective with cultivar BS 4. Fungal infectivity could not be related with endophyte effectiveness at stimulating plant growth, although the percentage of root length infected by each one of the threeGlomus species did not vary between cultivars. Genetic differences among plant cultivars can thus markedly affect the symbiosis between the host root and VAM fungi; this suggests that potential host-endophyte combinations need to be evaluated before being tested in the field.     

Presence of specific polypeptides in onion roots colonized by Glomus mosseae

We studied changes in gene expression during the establishment of vesicular-arbuscular (VA) mycorrhizal symbiosis. Polypeptides were obtained by in vitro translation of total root RNA extracted from VA-colonized and noncolonized root-tissue of onion (Allium cepa L. cv. Babosa), and resolved by two-dimensional polyacrylamide gel electrophoresis. VA mycorrhization led to a specific appearance of eight new polypeptides, and the disappearance of seven polypeptides in VA-colonized root. Our findings indicate that gene expression is altered in response to morphological and physiological changes resulting from the establishment of VA mycorrhizas.     

Vesicular-arbuscular mycorrhizae in a wastewater-irrigated oldfield ecosystem in Michigan

The incidence of vesicular-arbuscular mycorrhizae (VAM) in wastewater irrigated and non-irrigated oldfield soils in Michigan was studied. Soil and root samples were taken monthly from field plots on the second and third years of consecutive irrigation with municipal wastewater at rates of 0, 5 and 10 cm wk^–1. The oldfield ecosystem contained a high VAM fungal spore population density, but low species diversity. The most common VAM fungal species were Glomus mosseae and G. fasciculatum. Both spore density and root colonization were higher in irrigated than in non-irrigated plots. Irrigation effects were largest early in the growing season. In addition to increasing VAM incidence, wastewater irrigation shifted VAM fungal species composition. Irrigation favored G. mosseae over G. fasciculatum. Bioassays using either Sorghum vulgare or Daucus carota, an oldfield native species, indicated that the VAM systems were still functioning after the third year of consecutive wastewater irrigation. The data from experiments using nutrient solutions at wastewater concentrations suggest that the effects of wastewater irrigation on VAM are due to the effects of both water and nutrients. Since VAM are a very important component of the plant's water and nutrient uptake system and equally important in structuring plant communities under limiting growth conditions, it is suggested that the stimulatory effect of wastewater irrigation on VAM in an oldfield ecosystem enhances the ecosystem's ability to function as a living filter for wastewater clean up.Michigan Agricultural Experimental Station Journal Article No 13137.On sabbatical leave from ESAL, Lavras-MG, Brazil