Effects of calcium on cadmium uptake and transport in the tree species Gamblea innovans

The effect of calcium (Ca) on cadmium (Cd) accumulation in plants was investigated using Gamblea innovans Sieb. & Zucc., a deciduous tree species that is an accumulator plant for Cd and zinc (Zn). Saplings of G. innovans were grown for 3 months and fed with solutions containing only Ca (+Ca), both Ca and Cd (Ca+Cd), or only Cd (+Cd). The Ca concentration in roots was higher in both treatments containing Cd alone (+Cd) and Ca+Cd compared to roots treated with Ca alone (+Ca). In addition, the Cd concentration in roots was higher in the Ca+Cd treatment than the Cd treatment. This showed that the presence of Ca²⁺ in the rhizosphere relates with Cd uptake into roots. The result that the transport of Cd from roots through stem to leaves was suppressed by Ca treatment indicates that the presence of Ca regulates Cd transport from the roots. A clear correlation between Cd and Zn concentrations in leaves suggests a possibility that the Cd treatment accelerates the transport of Zn into leaves via the same protein transporter in this species.     

Characterizing nicotianamine aminotransferase: Improving its assay system and details of the regulation of its activity by Fe nutrition status

Under iron deficient conditions, graminaceous plants secrete mugineic acid family phytosiderophores (MAs) from their roots to dissolve sparingly soluble iron compounds in the rhizosphere, and take up iron in the form of an Fe³⁺-MAs complex (Takagi 1976). A good correlation has been reported between the tolerance of Fe-deficiency and the amount of secreted MAs (Takagi 1993). Therefore, by using the genes involved in MAs biosynthesis, molecular breeding might produce transgenic plants tolerant to Fe-deficiency with a high level of MAs secretion. The biosynthetic pathway of MAs from L-methionine has been clarified (Fig. 1) and the enzymes participating in this process are now being investigated to isolate the genes responsible. Nicotianamine aminotransferase (NAAT) catalyzes the amino group transfer between nicotianamine (NA) and 2-oxoglutaric acid (Fig. 1). In order to purify NAAT, enzyme assay methods for NAAT have been developed and modified (Shojima et al. 1990; Ohata et al. 1993; Kanazawa et al. 1994). Some characteristics of NAAT have been reported using these enzyme assay methods (Kanazawa et al. 1994, 1995). Here, we further investigate some characteristics of this enzyme to improve the enzyme assay method, namely 1) the effect of K⁺ and Mg²⁺ on NAAT activity in vitro, and 2) the direct influence of MAs, Fe³⁺, and Fe²⁺ on NAAT activity. In addition, based on these results, the induction of enzyme activity by Fe-deficiency and suppression of the activity by Fe-resupply was investigated, by applying the new enzyme assay method.     

A rapid and easy method of detecting levels of gene expression in intact tobacco plants using an Agrobacterium-mediated transient assay: Toward development of nutritional diagnosis based on gene expression

For the use of gene expression for nutritional diagnosis, a rapid and easy method of detecting levels of gene expression was proposed. Agrobacterium tumefaciens carrying the GUS reporter gene was injected into intact tobacco leaves with a plastic syringe, and transient GUS expression was determined. GUS activities were reproducible in young leaves.     

Time course study of aluminum-induced callose formation in barley roots as observed by digital microscopy and low-vacuum scanning electron microscopy

To clarify the mechanism(s) involved in the short-term inhibition of root elongation by AI, we monitored the morphological changes of barley roots by digital microscopy. Within 30 min after exposure to 37 µM AI, the surface of the root epidermis in the region of a distance of 1.5 mm from the root tip became rough and began to show signs of damage. After 38 min, callose was rapidly excreted from the junction between the root cap and the root epidermis, and formed a spherical lump approximately 60 µm in diameter. The fine structure of the callose deposits on the root surface was analyzed by low-vacuum scanning electron microscopy. After 50 min, there was a significant increase in the callose contents in the distal 0.6 mm part. At the same time, root elongation stopped completely. Fluorescence staining indicated that callose was localized on the surface of the cell elongation area (the elongation zone of primary roots and root hairs), but not on the surface of the meristem. The root growth reduction associated with AI treatment may be due to the use of sugar substrates for callose formation instead of cellulose formation.     

Effect of free-air CO2 enrichment on the storage of carbohydrate fixed at different stages in rice (Oryza sativa L.)

Increasing global atmospheric CO₂ concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO₂ (AMB) or free-air CO₂-enrichment (FACE) at CO₂ concentrations ranged from 275 to 365 μmol mol⁻¹ above AMB. We supplied ¹³CO₂ to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with ¹³C at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem ¹³C content. Furthermore, there were no differences between treatments in whole-plant ¹³C contents at heading and grain maturity. In contrast, plants supplied with ¹³C at the grain-filling stage had more ¹³C in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO₂ enrichment might be effectively stored in the grains. Furthermore, regardless of when the ¹³C was supplied, plants had more ¹³C in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO₂ enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains.     

Increase in Iron and Zinc Concentrations in Rice Grains Via the Introduction of Barley Genes Involved in Phytosiderophore Synthesis

Increasing the iron (Fe) and zinc (Zn) concentrations of staple foods, such as rice, could solve Fe and Zn deficiencies, which are two of the most serious nutritional problems affecting humans. Mugineic acid family phytosiderophores (MAs) play a very important role in the uptake of Fe from the soil and Fe transport within the plant in graminaceous plants. To explore the possibility of MAs increasing the Fe concentration in grains, we cultivated three transgenic rice lines possessing barley genome fragments containing genes for MAs synthesis (i.e., HvNAS1, HvNAS1, and HvNAAT-A and HvNAAT-B or IDS3) in a paddy field with Andosol soils. Polished rice seeds with IDS3 inserts had up to 1.40 and 1.35 times higher Fe and Zn concentrations, respectively, compared to non-transgenic rice seeds. Enhanced MAs production due to the introduced barley genes is suggested to be effective for increasing Fe and Zn concentrations in rice grains.     

Influence of ventral fixation techniques on atlantoaxial joint fusion in canine models with dens partial resection

We evaluated the completeness of bony fusion of the atlantoaxial joint (AAJ) through polymethylmethacrylate fixation (PMF) and atlantoaxial plate fixation (APF) using six canine models with dens partial resection. In both groups, the hydroxyapatite content at the AAJ was measured up to 7 months postoperatively using quantitative computed tomography. Histological assessment revealed fibrous fusion in the PMF group. Meanwhile, in the APF group, only one dog achieved fibrous fusion, whereas the remaining three showed bony fusion. To our knowledge, this study was the first to evaluate AAJ fusion histologically after PMF and APF. The present study demonstrates that PMF and APF may stabilize the AAJ without clinical complications. Therefore, PMF and APF are clinically useful fixation methods for atlantoaxial instability.     

Effect of sodium acetate on the adhesion to porcine gastric mucin in a Lactococcus lactis strain grown on fructose

The association of lactic acid bacteria with mucosal surfaces plays important roles in the beneficial effects of these bacteria on human health, such as colonization of the gastrointestinal tract for pathogen antagonism. Previously, we found that the adhesion of Lactococcus lactis 7‐1 to porcine gastric mucin was higher with fructose than with lactose, galactose or xylose as the carbon source. In this study, we examined the effect of growth conditions on the adhesion of strain 7‐1 grown on fructose. Medium components affect the adhesion: the adhesion of strain 7‐1 grown with sodium acetate was higher than that without it. The enhancement of adhesion by sodium acetate was not observed under aerobic conditions. Cellular properties grown with or without sodium acetate were characterized: strain 7‐1 grown with sodium acetate had similar sugar contents, and different fatty acid composition to those grown without it. Strain 7‐1 grown with sodium acetate showed significantly lower cell yield and significantly higher hydrophobicity than those grown without it, which is associated with higher adhesion. Fructose and sodium acetate are frequently used in the food industry; this study may reveal a simple way to enhance the adhesion of lactic acid bacteria by growing them with these substances.