We previously reported that Tricholoma matsutake and Tricholoma fulvocastaneum, ectomycorrhizal basidiomycetes that associate with Pinaceae and Fagaceae, respectively, in the Northern Hemisphere, could interact in vitro as a root endophyte of somatic plants of Cedrela odorata (Meliaceae), which naturally harbors arbuscular mycorrhizal fungi in South America, to form a characteristic rhizospheric colony or "shiro". We questioned whether this phenomenon could have occurred because of plant-microbe interactions between geographically separated species that never encounter one another in nature. In the present study, we document that these fungi formed root endophyte interactions and shiro within 140 days of inoculation with somatic plants of Prunus speciosa (=Cerasus speciosa, Rosaceae), a wild cherry tree that naturally harbors arbuscular mycorrhizal fungi in Japan. Compared with C. odorata, infected P. speciosa plants had less mycelial sheath surrounding the exodermis, and the older the roots, especially main roots, the more hyphae penetrated. In addition, a large number of juvenile roots were not associated with hyphae. We concluded that such root endophyte interactions were not events isolated to the interactions between exotic plants and microbes but could occur generally in vitro. Our pure culture system with a somatic plant allowed these fungi to express symbiosis-related phenotypes that varied with the plant host; these traits are innately programmed but suppressed in nature and could be useful in genetic analyses of plant-fungal symbiosis.
The effects of salinity on the seedlings of five acacia species, Acacia ampliceps, A. salicina, A. ligulata, A. holosericea, and A. mangium were studied with respect to mortality, growth, and proline accumulation. There was marked variation among the species in their response to salinity. A. ampliceps showed the highest level of salt tolerance among the five acacia species. In contrast, A. holosericea and A. mangium were classified as the least tolerant. The concentration which caused 100% mortality in 2-week-old seedlings during 1 week of treatment was 2.5% (w/v) and 1.5% NaCl for A. ampliceps and A. holosericea, respectively. The dry weights of whole plant of two acacia species decreased markedly under the above salt stress conditions. Proline accumulation was found in leaves and roots after NaCl treatment. The maximum level of proline accumulation in A. holosericea was about twice as great as that in A. ampliceps throughout the stress period. Thus, the level of proline accumulation was not related to the degree of salt tolerance in these acacia species, although a positive correlation between the extent of salt stress and the accumulation of proline was found.
BoletalesEndophyte Symbiosis a b s t r a c t Suillus luteus (Boletales, Agaricomycetes) associates solely with Pinaceae species as an ectomycorrhizal symbiont in the Northern Hemisphere. Prunus speciosa (Rosaceae) andCedrela odorata (Meliaceae) naturally harbor arbuscular mycorrhizal fungi. The present study documents that S. luteus establishes root endophyte symbioses in vitro with somatic Prunus speciosa; however, it does not penetrate root tissues of somatic Cedrela odorata. With P. speciosa, the hyphae of S. luteus were heavily entangled in the intercellular space, unlike the rather straight hyphae of Tricholoma matsutake (Agaricales, Agaricomycetes). With C. odorata, S. luteus colonized only the surface of the exodermis and exhibited dark-brown mycorrhizalike morphology. Prunus speciosa associated with S. luteus grew significantly better than that without the fungus, but C. odorata did not show significant beneficial effects when growing with the fungus. The data indicate that apparent Pinaceae-specific ectomycorrhizal fungi associate with arbuscular mycorrhizal broad-leaved plants in vitro, although the physical characteristics of the interactions vary depending upon the plant and fungal species.
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