Real-time imaging of nitrogen fixation in an intact soybean plant with nodules using 13N-labeled nitrogen gas

Real-time images of nitrogen fixation in an intact nodule of hydroponically cultured soybean ( Glycine max [L] Merr.) were obtained. In the present study, we developed a rapid method to produce and purify ¹³N-labeled radioactive nitrogen gas (half life: 9.97 min). ¹³N was produced from a ¹⁶O (p, α) ¹³N nuclear reaction. The target chamber was filled with CO₂ and irradiated for 10 min with protons at an energy of 18.3 MeV and an electric current of 5 μA, which was delivered from a cyclotron. All CO₂ in the collected gas was absorbed and removed with powdered soda-lime in a syringe and replaced with helium gas. The resulting gas was injected into gas chromatography and separated and a 35 mL fraction, including the peak of [¹³N]-nitrogen gas, was collected by monitoring the chromatogram. The obtained gas was mixed with 10 mL of O₂ and 5 mL of N₂ and used in the tracer experiment. The tracer gas was fed into the underground part of intact nodulated soybean plants and serial images of the distribution of ¹³N were obtained non-invasively using a positron-emitting tracer imaging system (PETIS). The rates of nitrogen fixation of the six test plants were estimated to be 0.17 ± 0.10 μmol N₂ h⁻¹ from the PETIS image data. The decreasing rates of assimilated nitrogen were also estimated to be 0.012 ± 0.011 μmol N₂ h⁻¹. In conclusion, we successfully observed nitrogen fixation in soybean plants with nodules non-invasively and quantitatively using [¹³N]N₂ and PETIS.     

Ultralong-range polaron-induced quenching of excitons in isolated conjugated polymers

In conjugated polymers, radiative recombination of excitons (electron-hole pairs) competes with nonradiative thermal relaxation pathways. We visualized exciton quenching induced by hole polarons in single-polymer chains in a device geometry. The distance-scale for quenching was measured by means of a new subdiffraction, single-molecule technique--bias-modulated intensity centroid spectroscopy--which allowed the extraction of a mean centroid shift of 14 nanometers for highly ordered, single-polymer nanodomains. This shift requires energy transfer over distances an order of magnitude greater than previously reported for bulk conjugated polymers and far greater than predicted by the standard mechanism for exciton quenching, the unbiased diffusion of free excitons to quenching sites. Instead, multistep "energy funneling" to trapped, localized polarons is the probable mechanism for polaron-induced exciton quenching.     

Isolation and identification of flavonoids accumulated in proanthocyanidin-free barley

Flavonoids accumulated in proanthocyanidin-free near-isogenic lines iso ant 13, iso ant 17, and iso ant 22 of Nishinohoshi, developed by backcross breeding using a leading cultivar, Nishinohoshi, as a recurrent parent and a proanthocyanidin-free mutant as a nonrecurrent parent in Japan, were examined. A new flavanone, (2RS)-dihydrotricin 7-O-β-D-glucopyranoside (1), known flavanones (2RS)-dihydrotricin (2) and (2RS)-homoeriodictyol (3), and known flavones chrysoeriol 7-O-[α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside] (4), chrysoeriol 7-O-β-D-glucopyranoside (5), tricin (6), and chrysoeriol (7) were isolated from iso ant 17 of Nishinohoshi. The structures and stereochemistries of the isolated flavonoids (1-7) were elucidated on the basis of spectroscopic analyses. The concentrations of the isolated flavonoids (1-7) in iso ant 13, iso ant 17, and iso ant 22 of Nishinohoshi were similar to each other, whereas the flavonoids 1-5 and 7 were not detected in Nishinohoshi, an old Japanese cultivar, Amaginijo, and North American cultivar Harrington. The concentration of tricin (6) in Nishinohoshi was a half those in iso ant 13, iso ant 17, and iso ant 22 of Nishinohoshi. Except for iso ant 13, iso ant 17, and iso ant 22 of Nishinohoshi, the concentration of tricin (6) was highest in Nishinohoshi, followed by Amaginijo and Harrington. Thus, tricin (6), its precursor dihydrotricin (2), and its glucopyranoside, dihydrotricin 7-O-β-D-glucopyranoside (1), as well as chrysoeriol (7) and homoeriodictyol (3) were accumulated in iso ant 13, iso ant 17, and iso ant 22 of Nishinohoshi probably by blocking at the step of flavanone 3-hydroxylase in the procyanidin biogenetic pathway, resulting in enhancement of the alternative biogenetic pathway.     

Isolation and Caenorhabditis elegans lifespan assay of flavonoids from onion

The main flavonoids were isolated from three selected onion cultivars. Three phenolic compounds were obtained by reverse-phase HPLC, and their structures were elucidated by multiple NMR measurements. There were two known compounds, quercetin and quercetin 3'-O-β-D-glucopyranoside (Q3'G), and one novel compound, quercetin 3-O-β-D-glucopyranoside-(4→1)-β-d-glucopyranoside (Q3M), which was identified in onion for the first time. These flavonoids were found to be more abundant in the onion peel than in the flesh or core. Their antioxidative activities were tested using the DPPH method, and their antiaging activities were evaluated using a Caenorhabditis elegans lifespan assay. No direct correlation was found between antioxidative activity and antiaging activity. Quercetin showed the highest antioxidative activity, whereas Q3M showed the strongest antiaging activity among these flavonoids, which might be related to its high hydrophilicity.     

Nutrients,Free Amino Acids,and Sugar Contents in Narcissus Roots Affected by N,P, K Deficiency during Winter

Non-rooted bulbs of Narcissus L. cv. “Garden Giant” were planted on October 25, 1993 and cultivated under N, P, or K deficiency or in complete medium (control). The roots emerged on November 5 and were sampled on March 7, 1994. The X-ray microanalyzer images showed the distribution of N, P, K, Ca, Mg, S, and Cl in a control root. The distribution of Cl was similar to that of K and also a similar distribution was found between Ca and S. There were significant differences in the concentration of N, P, K, Ca, Mg among treatments. Interaction among nutrient levels was observed. Control roots accumulated a large amount of nitrogen (84 mg g DW^-1) which was partitioned almost equally between the 80% ethanol soluble and insoluble fractions. N-deficient roots in the -N treatment, on the other hand, accumulated only about 12 mg g DW^-1 nitrogen, mostly in the insoluble fraction (83% of total N). Total amino acid contents responded to N, P, or K deficiency. Glutamine was a major free amino acid in control roots (17 mg N g DW^-1) and K-deficient roots (29 mg N g DW^-1), while arginine seemed to be the predominant amide in P-deficient roots. Content of total soluble sugars in the control, -P and -K treatments that was 49, 46, and 49 mg g DW^-1, respectively, was lower than in the -N treatment (137 mg g DW^-1). Mono- and disaccharides; fructose, glucose, and sucrose, were found in narcissus roots.