Metal hyperaccumulators are defined as plants containing extremely high concentrations of metals in their shoots. Several subspecies of Arabidopsis halleri hyperaccumulate Zn/Cd and are closely related to the genetic model plant A. thaliana. In this review, the recent progress of the characterization of metal accumulation in A. halleri were summarized, especially in A. halleri ssp. gemmifera, growing in East Asia. We also focused on the intraspecific natural variation to elucidate the metal homeostasis in A. halleri ssp. gemmifera, and collected the accessions from a limestone mining site on Mt. Ibuki, and compared them with those collected from non-calcareous soil in Japan. The plants growing on non-calcareous soil also accumulated Zn in shoot tissues, but shoot Zn concentrations in plants growing on calcareous soils were below the level required for hyperaccumulators. Furthermore, comparing analyses of Arabidopsis spp. were discussed as a valuable tool for the elucidation of phenotypic differences, not only metal homeostasis but molecular evolution of self-fertilisation, chromosomal rearrangement.

View full abstract

Viroids, the smallest RNA pathogen, infect different kinds of horticultural and agricultural crop, and lead to marked quality deterioration in the case of symptomatic infection. It is apparent that their autonomous replication and systemic movement in plants fully depend on the host machinery, since the pathogens lack their own protein-coding genes, whereas how viroids cause disease remains elusive. A model of short interfering RNA (siRNA) derived from viroid RNA that disrupts host gene expression, followed by an abnormal morphological appearance, is more acceptable than those previously proposed. On the other hand, the application of siRNA to block viroid replication is a plausible strategy for the molecular breeding of viroid-resistant plants. Recent advancements in the knowledge of viroid biology, as well as our approach to molecular breeding for Chrysanthemum stunt viroid (CSVd)-resistant chrysanthemum, are briefly reported.

View full abstract

We investigated growth, yield and quality of paddy-rice'Hino Hikari'under whole basal fertilizer application using coated urea and organic fertilizer. The decrease of seed yield under the organic treatment was approximately 5% when compared to the control. The decrease can be mitigated by increasing the manure imput. The quality of rice grain and ingredient concerning taste were also constant among the treatments. We concluded that the organic fertilizer used in this study has almost the same performance with the chemical fertilizer.

View full abstract

[in Japanese]

View full abstract

Flowering time is one of most important traits to contribute the regional adaptability in rice. Recent molecular genetic studies reveal a lot of genes involved in controlling not only flowering time, but also yield related traits. In this study, We investigated the distribution patterns of the primary rachis-branches and the secondary rachis-branches, by using a Taiwanese rice variety 'Tachung 65' and its near isogenic lines for flowering time gene loci, Hd1, Ehd1 and Ghd7. To evaluate the pleiotropic effects on the grain distribution patterns, we applied two methods of two-dimension mapping and graphical evaluation based on the relative branching position of the primary branch. The experimental results showed that Ef1 reduced the numbers of the secondary branches, especially at the middle and bottom part of the primary branches in the panicle. Hd1 also reduced the numbers of the secondary branches at all parts of the primary branches in the panicle.

View full abstract

Phosphorus (P) is a macronutrient in plants. Plants usually suffer from P-deficiency stress because most of fertilized P in soil is rapidly fixed to unavailable forms to plants. Breeding tolerant varieties which are able to uptake and/or use P efficiently, is an effective solution to the stress and it also contributes to P resource saving in future. In this study, pyramiding of two kinds of P-deficiency induced QTL, qREP-6 and qACP-8 was conducted to improve an elite Japanese rice variety 'Koshihikari' by using crosses between substituted lines (SL) having an indica variety 'Kasalath' segments on chromosome 6 and 8. In P-deficient solution experiment, Kasalath allele of qREP-6 and qACP-8 showed significant increase of root length and acid phosphatase activity in lower leaves, respectively, and their interaction was detected for P content of youngest fully expanded leaf using SL-F₂. In low P field experiment, a SL-F₃ line having Kasalath alleles of both QTLs showed significant increase of panicle number and weight. These results indicated that QTL pyramiding improved P deficiency tolerance of Koshihikari.

View full abstract

Short-term rice cultivars, "Fujihikari" and "Hanahyogo", were cultivated in both direct-seeding and transplanting methods with two levels of planting density, low and high. Rice dry weight and nitrogen uptake were measured through rice growth stages and at the mature stage yield and yield components were measured. Yielding ability when cultivated in directseeding with high planting density was the highest in Fujihikari, while yielding ability when cultivated in transplanting with high planting density was the highest in Hanahyogo. In both cultivars, rice dry weight with high planting density were higher than that with low planting density through rice growth stages. In Fujihikari, at mature stage rice dry weight when cultivated in direct-seeding with high planting density was the highest among all the cultivation methods, while in Hanahyogo at mature stage rice dry weight when cultivated in transplanting with high planting density was the highest among all the cultivation methods. In both cultivars, nitrogen uptakes with high planting density were higher than that with low planting density through rice growth stages. In Fujihikari, at mature stage the values of nitrogen uptake were almost the same without the value when cultivated in transplanting with low plant density, while in Hanahyogo the values of nitrogen uptake with high planting density were higher than the values with low planting density. It was revealed that to obtain much dry weight in early growth stage with high planting density is important in order to obtain high yield in short-term rice cultivars. In addition, it may be necessary to select the adequate cultivation method, either direct-seeding or transplanting, for each rice cultivar.

View full abstract

We investigated the effects of soil incorporation of hairy vetch (Vicia villosa Roth) on the growth of weeds and lowland rice plants in Hyogo Prefecture, western Japan. The cover and biomass of the most dominant weed Monochoria vaginalis were reduced proportionally with the amount of incorporated vetch plants, but not to the level commonly achieved by herbicides. Hairy vetch incorporation also increased the number of tillers and panicles of rice plants, which eventually led to a significant increase of rice yield which was equivalent to the addition of 41-56 panicles per square meter.

View full abstract

For micropropagation of soybean, somatic embryo induction from immature cotyledons followed by proliferation, maturation, and conversion culture method is widely used in the world. This protocol is well established with the model cultivar, Jack, however it is also known that the optimal conditions are highly depending on the genotypes. The Japanese elite black soybean, Tanbaguro is one of those recalcitrant varieties. We have been modifying Jack's protocol and obtained regenerated plants even though the efficiency was still low. During these experiments, we found replacing sucrose to maltose is efficient for not only maturation culture but also proliferation culture. In general, Jack's embryogenic cells will gradually lose the regeneration potential over two years of proliferation culture. However replacing sucrose to maltose in proliferation culture showed a remarkable recovery of regeneration potential of Jack cells that had completely lost the potential once after long-term (over three years) suspension culture. And this response caused by sucrose-maltose exchange was found to be reversibly occurring.

View full abstract

A slender glume mutant line IM294, which was induced with gamma irradiation of seeds of Gimbozu, has a nonfunctional Rurm1 (Rice ubiquitin-related modifier-1) gene. Yeast Urm1p, which shares about 41% sequence identity with RURM1, involves in oxidative stress response via the posttranscriptional modification of antioxidant protein Ahp1p, indicating that Rurm1 may function in the oxidative stress response in rice. In this study, we evaluated sensitivity against methylviologen (MV) to elucidate the role of Rurm1 in oxidative stress response in rice. Although the chlorophyll content largely decreased with the increase of MV concentration, there was no significant difference about the degree of decreased chlorophyll content between Gimbozu and IM294. It was therefore indicated that Rurm1 did not involve in the stress defense mechanism against MV in rice.

View full abstract