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Ribosomal intergenic transcribed spacer analysis (RISA) and automated RISA (ARISA) are used for analyzing microorganisms associated with stems and roots of nonnodulated ([Nod.sup.-]), wild-type nodulated ([Nod.sup.+]) and hypernodulated ([Nod.sup.++]) soybeans. The results have shown that the microbial community in [Nod.sup.-] soybeams is similar to that in [Nod.sup.++] soybeans than to that in [Nod.sup.+] soybeans.

Large quantities of Fe and Cd accumulate in the leaves of the metal-accumulating leguminous plant, Crotalaria juncea. A member of the metal transporter NRAMP family was cloned from C. juncea. The amino acid sequence of this clone, designated CjNRAMP1, was similar to the sequence of Arabidopsis AtNRAMP1, which is involved in Fe and Cd transport. Organ-specific analysis showed that CjNRAMP1 mRNA was expressed mainly in the leaves of C. juncea plants, as well as in stems and roots. Use of green fluorescent protein fused to CjNRAMP1 suggested its localization to the plasma membranes of plant cells. Complementation experiments using yeast strains with impaired metal transport systems showed that CjNRAMP1 transported both Fe and Cd in an inward direction within the cells. Transgenic Arabidopsis plants overexpressing CjNRAMP1 showed high tolerance to Cd, with Cd translocation from roots to leaves being substantially greater in transgenic than in wild-type plants. Overexpression of CjNRAMP1 resulted in a greater accumulation of Fe in shoots and roots, suggesting that CjNRAMP1 recognizes Fe and Cd as substrates and that the high Cd tolerance of CjNRAMP1 is due to its strong Fe uptake activity, even in the presence of high Cd concentrations in the rhizosphere. [ABSTRACT FROM AUTHOR]

The diversity of stem-associated bacteria of non-nodulated (Nod−), wild-type nodulated (Nod+) and hypernodulated (Nod++) soybeans were evaluated by clone library analyses of the 16S ribosomal RNA gene. Soybeans were dressed with standard nitrogen (SN) fertilization (15 kg N ha–1) and heavy nitrogen (HN) fertilization (615 kg N ha–1). The relative abundance of Alphaproteobacteria in Nod+ soybeans (66%) was smaller than that in Nod− and Nod++ soybeans (75–76%) under SN fertilization, whereas that of Gammaproteobacteria showed the opposite pattern (23% in Nod+ and 12–16% in Nod− and Nod++ soybeans). Principal coordinate analysis showed that the bacterial communities of Nod− and Nod++ soybeans were more similar to each other than to that of Nod+ soybeans under SN fertilization. HN fertilization increased the relative abundance of Gammaproteobacteria in all nodulation phenotypes (33–57%) and caused drastic shifts of the bacterial community. The clustering analyses identified a subset of operational taxonomic units (OTUs) at the species level in Alpha- and Gammaproteobacteria responding to both the nodulation phenotypes and nitrogen fertilization levels. Meanwhile, the abundance of Betaproteobacteria was relatively constant in all libraries constructed under these environmental conditions. The relative abundances of two OTUs in Alphaproteobacteria (Aurantimonas sp. and Methylobacterium sp.) were especially sensitive to nodulation phenotype and were drastically decreased under HN fertilization. These results suggested that a subpopulation of proteobacteria in soybeans is controlled in a similar manner through both the regulation systems of plant–rhizobia symbiosis and the nitrogen signaling pathway in plants. [ABSTRACT FROM AUTHOR]

To clarify the nutrient status in momi fir (Abies firmaSieb. et Zucc.) seedlings under complex stress conditions of acid fog with soil acidification or nitrogen loading, we exposed seedling shoots to simulated acid fog (pH 3) and simultaneously loaded the soil with acid or excess nitrogen for 17 months. Proton and nitrogen loading reduced K concentration in soil, but these treatments had little effect on the nutrient status of fine roots in momi fir seedlings. Acid fog exposure resulted in reduced concentrations of Mg, Al, and Fe in current-year needles and Mg, Al, Cu, Fe, and Zn in 1-year-old needles. The complex effects of acid fog exposure with proton or nitrogen loading on nutrient status were relatively slight. However, elements such as Al and Cu notably reflect the effects of proton loading. These results show that the nutrient status of trace elements, rather than major elements, in needles of momi fir seedlings is sensitive to exposure to acid fog or proton loading. [ABSTRACT FROM AUTHOR]