Shu Fujimaki

Destination-selective long-distance movement of phloem proteins

The phloem macromolecular transport system plays a pivotal role in plant growth and development. However, little information is available regarding whether the long-distance trafficking of macromolecules is a controlled process or passive movement. Here, we demonstrate the destination-selective long-distance trafficking of phloem proteins. Direct introduction, into rice (Oryza sativa), of phloem proteins from pumpkin (Cucurbita maxima) was used to screen for the capacity of specific proteins to move long distance in rice sieve tubes. In our system, shoot-ward translocation appeared to be passively carried by bulk flow. By contrast, root-ward movement of the phloem RNA binding proteins 16-kD C. maxima phloem protein 1 (CmPP16-1) and CmPP16-2 was selectively controlled. When CmPP16 proteins were purified, the root-ward movement of CmPP16-1 became inefficient, suggesting the presence of pumpkin phloem factors that are responsible for determining protein destination. Gel-filtration chromatography and immunoprecipitation showed that CmPP16-1 formed a complex with other phloem sap proteins. These interacting proteins positively regulated the root-ward movement of CmPP16-1. The same proteins interacted with CmPP16-2 as well and did not positively regulate its root-ward movement. Our data demonstrate that, in addition to passive bulk flow transport, a destination-selective process is involved in long-distance movement control, and the selective movement is regulated by protein–protein interaction in the phloem sap.

Quantitative estimation of the contribution of the phloem in cadmium transport to grains in rice plants (Oryza sativa L.)

Abstract The contribution of the phloem in translocation of cadmium (Cd) to grains of rice plants (Oryza sativa L. cv. Kantou) was estimated. We measured Cd concentrations in phloem sap collected from the uppermost internode of rice plants at the grain-filling stage. Cadmium concentration was 17.8 ± 4.5 µmol L−1 in plants treated with a nutrient solution containing 10 µmol L−1 Cd for 2 days. Subsequently, distribution ratios of 109Cd between the grains and the glumes were determined after feeding of 109Cd to the cut ends of the uppermost internodes or onto the surface of the flag leaves or to the roots. The results suggested that 91–100% of the Cd in the grains was deposited from the phloem. To our knowledge, this is the first determination of Cd concentrations in phloem sap transported to grains, and the first estimation of the contribution of the phloem in Cd transport to rice grains.

Effect of Nitrate on Nodulation and Nitrogen Fixation of Soybean

1.1 Biological nitrogen fixation and nitrogen nutrition in soybean plants Biological nitrogen fixation is one of the most important processes for ecosystem to access available N for all living organisms. Although N2 consists 78% of atmosphere, but the triple bond between two N atoms is very stable, and only a few group of prokaryotes can fix N2 to ammonia by the enzyme nitrogenase. Annual rate of natural nitrogen fixation is estimated about 232 x 106 t, and the 97% depends on biological nitrogen fixation (Bloom, 2011). This exceeds the rate of chemical nitrogen fertilizer uses about 100 x 106 tu0e00in 2009. Soybean can use N2, though symbiosis with nitrogen fixing soil bacteria, rhizobia, to make root nodules for harboring them. Soybean (Glycine max [L.] Merr.) is a major grain legume crop for feeding humans and livestock. It serves as an important oil and protein source for large population residing in Asia and the American continents. The current global soybean production was 231 x 106 t in 2008 (FAOSTAT). It is a crop predominantly cultivated in U.S.A., Brazil, Argentina and China, which together contribute nearly 87 percent of the total world produce in 2008. Soybean has become the raw materials for diversity of agricultural and industrial uses. Soybean seeds contain a high proportion of protein, about 40% based on dry weight, therefore, they require a large amount of nitrogen to get a high yield. About 8 kg N is required for 100 kg of soybean seed production. Soybean can use atmospheric dinitrogen (N2) by nitrogen fixation of root nodules associated with soil bacteria, rhizobia. Soybean plants can absorb combined nitrogen such as nitrate for their nutrition either from soil mineralized N or fertilizer N. It is well known that heavy supply of nitrogen fertilizer often causes the inhibition of nodulation and nitrogen fixation. Therefore, only a little or no nitrogen fertilizer is

Wounding inducibility of axil gene, which induces auxin independent cell division of tobacco protoplast

In order to elucidate the function of axil, which is directing auxin independent growth in tobacco (Nicotiana tabacum) protoplasts, the expression pattern of the gene was examined under various conditions. It has been shown previously that axi1 is expressed mainly in root and apical meristem in cells which are frequently dividing. We wish to know how plant cell division is controlled in relation with the expression of axi1 gene. Since wounding induces dedifferentiation and cell division, the effect of wounding on axi1 expression was investigated by the method of reverse transcription-polymerase chain reaction (RT-PCR). Data we presented which show accumulation of axi1 mRNA stimulated by mechanical wounding not only on the wounded leaves but also on the adjacent unwounded leaves.

Cloning of axil-like cDNA from soybean

In A cDNA showing high similarity to axi1 (auxin independent growth) of tobacco (Nicotiana tabacum) was cloned from soybean (Glycine max). The sequences from soybean and tobacco were identical except for their N-termini and C-termini.