Summary• Interactions between a mycorrhiza-defective tomato ( Lycopersicon esculentum ) mutant, rmc , and different species of arbuscular mycorrhizal (AM) fungi were investigated and compared with those with the wild-type cv. 76R.• Both cv. 76R and rmc were challenged with Glomus intraradices , G. mosseae , G. coronatum, G. versiforme , G. etunicatum , G. fasciculatum , Gigaspora margarita and Scutellospora calospora using a nurse pot inoculation system.• Cv. 76R demonstrated normal colonization patterns for all fungal species. By contrast, the development of different fungal species with rmc was impaired at different steps. Development of G. intraradices , G. etunicatum and G. fasciculatum was arrested on the root surface. However, G. mosseae , G. coronatum , G. margarita and S. calospora frequently penetrated the root epidermis, but colonization of the cortex was rare. G. versiforme achieved relatively normal colonization in rmc compared with the other species.• This is the first report on the variation of colonization patterns in a mycorrhizadefective mutant by different species of AM fungi, and highlights the need for previously described mutants in legumes to be challenged by more than one fungus.

In this study the presence and orientation of fungal microtubules were recorded in arbuscular mycorrhizal symbiosis for the first time. Visualization of the fungal microtubules was achieved by using a protocol specifically labelling only fungal tubulins. Microtubules of external mycelium, intraradical hyphae, arbuscules, and vesicles of the arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith were examined when in symbiosis with tomato (Lycopersicon esculentum Mill.). Microtubules were organized as bundles in both external and intraradical hyphae. The bundles of microtubules extended directly from intraradical hyphae into the arbuscules, where the microtubules remained as bundles in the larger hyphae. In the fine fungal branches of the arbuscules, microtubules were seen as thinner filaments. Fungal microtubules were seen to connect the intraradical hyphae and arbuscules. In addition, microtubules of adjacent arbuscules could continue directly from one arbuscule to another. Microtubules reached to the basal cone of each vesicle, but the live vesicles, containing many nuclei, seemed devoid of any microtubular labelling.Key words: cytoskeleton, endomycorrhiza, filamentous fungi, tomato, tubulin, Zygomycota.

This investigation was initiated to assess whether inoculation of cashew (Anacardium occidentale) seedlings under commercial nursery conditions would result in mycorrhizal development in the root systems and increased growth of the plants. Three experiments were carried out to investigate the effects of different nursery factors on infection and plant growth. These were: use of triple superphosphate, pH of the potting mix (varied by lime additions) and removal of the cotyledons. Inoculation with the commercially available mycorrhizal inoculum Nutrilink� (containing spores of Glomus intraradices) resulted in mycorrhiza formation, but the levels of infection were low even in the absence of triple superphosphate addition. The highest infection (55%) was observed in seedlings from which the cotyledons had been removed. Inoculated plants in general grew less well than non-inoculated plants under all conditions. This depression may be the result of changes in pH following inoculation or the result of development of mycorrhizal infection. There were no positive effects of inoculation on nutrient concentrations in the tissues, except that inoculated plants had higher concentrations of K in both leaves and roots. Addition of lime to the potting mix did not significantly affect the extent of infection or the responses of the plants. Cotyledon removal was associated with higher infection and a reduction in the negative effect of inoculation on growth, although plant growth was reduced in inoculated and non-inoculated treatments. It does not appear that inoculation with NutriLink is appropriate in the potting mixes used, particularly as the formulation causes changes in pH of the potting mixes. Other strategies will need to be adopted to optimize potential benefits of mycorrhizas in cashew production.

The xanthene dyes sulforhordamine G, phloxine B, rose Bengal, and 4,5,6,7-tetrachloroflorescein were used as fluorochromes for laser scanning confocal microscopy of LR-White resin-embedded mycorrhizae. Sulforhodamine G was the most effective dye, giving an even staining of cell components throughout the material, with minimal background fluorescence of LR-White resin. Confocal microscopy of stained blocks of tissue on a slide, viewed without the use of a coverslip, revealed the three-dimensional nature of various mycorrhizal structures; these structures included arbuscules, vesicles, and coiled hyphae in arbuscular mycorrhizae; coiled hyphae in orchid mycorrhizae; mantle and Hartig net hyphae in ectomycorrhizae; and intracellular hyphae in arbutoid mycorrhizae. Sections mounted on slides viewed with confocal microscopy provided exceptional clarity of fungal form and cytoplasmic contents and showed the relationship to the plant cells, also with negligible background fluorescence. Mounting and staining blocks of resin-embedded material provided a fast and effective technique for the visualization of a variety of plant and fungal tissues. Stain penetration in whole-mounted samples was sufficient to reconstruct clear three-dimensional images using confocal microscopy.Key words: mycorrhizae, xanthene dyes, confocal microscopy, resin embedding.

The expression patterns of the cytoskeletal proteins α-, β-, and γ-tubulin, actin, and myosin were investigated in young tomato roots and older roots at different intensities of mycorrhizal colonization. The relative level of cytoskeletal proteins was estimated by protein blotting and immunostaining. The contribution of plant α-, β-, and γ-tubulin to the total protein pool was higher in uncolonized 2-week-old roots than in 10-week-old roots, whereas the contribution of actin remained constant. The level of plant tubulin expression was clearly higher in mycorrhizal root systems than in uncolonized older root systems. These results indicate that tubulins are more involved in plant cell differentiation than actin. Myosin of approximately 230 kDa was expressed in the roots of 10-week-old wild-type tomato but not in young or mycorrhizal tomatoes. In contrast, a smaller ca. 170 kDa myosin was consistently present in all root samples. Indirect immunofluorescence microscopy showed that plant myosin was located particularly along the periarbuscular membranes surrounding the arbuscule branches. In uncolonized roots, myosin was associated mainly with membranes adjacent to plant cell walls. These data provide novel evidence that myosin expression and localization in root cells responds to mycorrhizal colonization.Key words: actin, myosin, arbuscular mycorrhizal fungi, protein expression, tubulin.