Metallothioneins (MTs) are a superfamily of low molecular weight, metal-binding proteins found in diverse organisms including animals, plants, and fungi as well as some prokaryotes. The ability of MTs to bind metal ions is their most notable function. MTs play an important role in metal ion homeostasis in plants and metal ion detoxification.
In this study, the plant MT1 genes from rice and Chloris virgata were used to analyse those functions in plant. The expressions of ChlMT1a, OsMT1a, and OsMT1b genes were analysed under stresses from metals. To investigate the function of MT1s, we transformed yeast with an expression vector containing MT1 cDNAs, respectively, and checked those growths under various stresses. Arabidopsis was transformed with the three MT1s. The phenotypes transgenic Arabidopsis, for example environmental stress tolerances were analysed to investigate the functions of MT1s in plant.

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We have isolated Cd-tolerant clones from natural habitat plants growing in a former mining site. Of those, we further characterize a cDNA, termed DcCDT1, from Digitaria ciliaris. It confers Cd tolerance to the yeast cells which accumulate almost 2-fold lower Cd levels than control cells. DcCDT1 cDNA encodes a cysteine-rich-peptide composed of 55 amino acid residues. Five DcCDT1-homologues are found in rice and termed OsCDT1-5. All of them are up-regulated to varying degrees in above-ground tissues upon CdCl2 treatment. Localization of GFP fusions suggests that DcCDT1 and OsCDT1 are targeted to the cellular boundary in plant cells. Transgenic A. thaliana plants overexpressing DcCDT1 or OsCDT1 display a CdCl2-tolerant phenotype and, consistent with our yeast data, contain lower amounts of Cd when grown on CdCl2. Collectively, our data suggest that DcCDT1 and the related peptide function to prevent Cd entry into yeast and plant cells.

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The feasibility of bacterial heavy metal transporter, MerC, for environmental phytoremediation of mercury and cadmium pollution was investigated. The bacterial merC was fused with Arabidopsis AtVAM3, a gene determining foreign molecule targeting to vacuolar membrane, and transformed into Arabidopsis. In the present study, we found that the transgenic plants expressing MerC-AtVAM3 protein accumulated more metals in the vacuolar than its wild-type progenitors. These results suggest that the transgenic plants might provide a means for phytoremediation of metal pollutions.

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Oilseed rape (Brassica napus L.) is one of the most important oil crops for food oil as well as the materials for biofuel. In order to know growth condition of the plant in relation to the quality of the oil, the nutrient movement in the plant sample is very important. However there are not so many studies focusing on the elemental analysis. Therefore, we performed elemental analysis of B. napus (Kizakinonatane, Kirariboshi, Westar) seeds and plants using SEM-EDS, ICP-AES and X-ray fluorescence instrument. As a result, the concentration of sulfur showed characteristic features among the cultivars. Therefore, we used ³⁵S labeled sulfate to analyze the distribution and movement of sulfur within the plants using an imaging plate. Then we studied the real-time uptake manner of sulfur in the plant. This research was performed under collaboration of Genesis Research Institute, Inc..

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Terrestrial plants utilize gravity (1g) as stress and signal factors for growth and morphogenesis. Their gravity-responses have been studied in relation to gravitropism or simulated microgravity conditions. Here we examined possible deteriorative or resistant responses of callus cells to hypergravity originated by centrifugation at 100g. Callus cells obtained from either suspension-cells or root tissues of tomato and broad bean were then grown on MS-agar media in centrifuge tubes. We found that the cell growth was strongly inhibited under 100g conditions for 2-4days. However, the growth was partially recovered after 4days, suggesting that the cells accommodated to the hypergravity conditions with tolerance characteristics developed. Under 100g conditions, cell wall synthesis was strongly inhibited and intracellular levels of soluble sugars, thiols and some enzymatic activities for primary sugar-metabolisms increased temporarily in the earlier hypergravity responses. Following these, growth recovery responses involved the total increase of cell wall contents in the cells.

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Buckwheat is known to accumulate methanol-insoluble proanthocyanidin (PAS-Cya) in leaves, seeds and flowers. However, physiological roles of PAS-Cya are not clarified. To investigate them, we compared PAS-Cya accumulation in natural type and mutant buckwheat, which accumulates little amount of PAS-Cya. We used Tartary buckwheat leaves as materials. PAS-Cya was stained using dimethylaminocinnamaldehyde(DMACA). In mutant leaves, it had some disease-like spots, which contained anthocyanins. Mutants accumulated PAS-Cya only in the spots. On the other hand, natural type leaves had no spots, and it accumulated PAS-Cya in the whole parts of leaves. We also investigate PAS-Cya accumulation in longitudinal section of leaves. In mutant, PAS-Cya was accumulated only in the palisade and spongy layer of spots. On the other hand, natural type contained PAS-Cya in whole parts of epidermis, palisade and spongy layer. These results indicate that PAS-Cya accumulation has important relation to spots generation and inhibition of its magnification.

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In this study, we investigated the role of JA in phytoalexin production in rice using the JA-deficient cpm2 mutant. Firstly, it was confirmed that wound-induced production of JA was severely suppressed in cpm2 plants. Then we performed quantification of phytoalexins in CuCl2-treated rice leaves. The mutant leaves showed no significant difference from wild-type leaves in CuCl2-induced production of diterpenoid phytoalexins such as momilactones and phytocassanes. On the other hand, CuCl2-induced production of the flavonoid phytoalexin sakuranetin was severely suppressed in cpm2 leaves. This suppression was cancelled by the addition of JA. These data suggest that JA or metabolically related compounds are essential for the production of sakuranetin, but not for the production of diterpenoid phytoalexins.

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