Isoflavones play important roles in plant-microbe interactions in rhizospheres. Soybean roots secrete daidzein and genistein to attract rhizobia. Despite the importance of isoflavones in plant-microbe interactions, little is known about the developmental and nutritional regulation of isoflavone secretion from soybean roots. In this study, soybeans were grown in hydroponic culture, and isoflavone contents in tissues, isoflavone secretion from the roots, and the expression of isoflavone conjugates hydrolyzing beta-glucosidase (ICHG) were investigated. Isoflavone contents did not show strong growth-dependent changes, while secretion of daidzein from the roots dramatically changed, with higher secretion during vegetative stages. Coordinately, the expression of ICHG also peaked at vegetative stages. Nitrogen deficiency resulted in 8- and 15-fold increases in secretion of daidzein and genistein, respectively, with no induction of ICHG. Taken together, these results suggest that large amounts of isoflavones were secreted during vegetative stages via the hydrolysis of (malonyl)glucosides with ICHG.

Isoflavones play important roles in rhizosphere plant-microbe interactions. Daidzein and genistein secreted by soybean roots induce the symbiotic interaction with rhizobia and may modulate rhizosphere interactions with microbes. Yet despite their important roles, little is known about the biosynthesis, secretion and fate of isoflavones in field-grown soybeans. Here, we analyzed isoflavone contents and the expression of isoflavone biosynthesis genes in field-grown soybeans. In roots, isoflavone contents and composition did not change with crop growth, but the expression of UGT4, an isoflavone-specific 7-O-glucosyltransferase, and of ICHG (isoflavone conjugates hydrolyzing beta-glucosidase) was decreased during the reproductive stages. Isoflavone contents were higher in rhizosphere soil than in bulk soil during both vegetative and reproductive stages, and were comparable in the rhizosphere soil between these two stages. We analyzed the degradation dynamics of daidzein and its glucosides to develop a model for predicting rhizosphere isoflavone contents from the amount of isoflavones secreted in hydroponic culture. Conjugates of daidzein were degraded much faster than daidzein, with degradation rate constants of 8.51 d-1 for malonyldaidzin and 11.6 d-1 for daidzin, vs. 9.15 × 10-2 d-1 for daidzein. The model suggested that secretion of isoflavones into the rhizosphere is higher during vegetative stages than during reproductive stages in field-grown soybean.

Investigations into the flow pattern and the void fraction for countercurrent air-water flow in vertical tubes of diameter D=40 and 80 mm were reported. The flow maps were presented and showed slug flow regime occupied larger portion on them. The void fraction was measured by the quick-closing valve technique, in bubbly and slug flow regime.The void fraction data available in the literatures as well as present work for countercurrent flow in vertical tubes were correlated in terms of dimensionless groups. The experimental results of the present work were also compared with the drift flux model.

Cerebral ischemic disorders are one of the main causes of death. In brain ischemia, blood flow disruptions limit the supply of oxygen and glucose to neurons, initiating excitotoxic events. These include activation of glutamate receptors and release of excess glutamate inducing neuron depolarization and significant increase of intracellular calcium, which activates multiple intracellular death pathways. 1 Accumulation of extracellular glutamate also inhibits cystine-glutamate exchanger, resulting in depletion of the intracellular antioxidant glutathione. 2,3 Under such conditions, reactive oxygen species are generated and implicated in neuronal cell death. 4 In this study, microbial metabolites were screened to find neuroprotective agents against glutamate toxicity.C6 rat glioma cells undergo cell death when exposed to 100 mM glutamate for 24 h. Thus, they provide a good model for evaluating neuroprotective activity against glutamate toxicity. Our screening using C6 cells resulted in the isolation of a new active compound designated as flaviogeranin (Figure 1) from Streptomyces sp. RAC226.The producing organism was cultivated in 500 ml Erlenmeyer flasks containing 100 ml of a medium consisting of glucose (2.5%), soybean meal (1.5%), dry yeast (0.2%) and calcium carbonate (0.4%) (pH 6.2, before autoclave) on a rotary shaker at 27 1C for 5 days. The culture broth (2 l) was centrifuged and the mycelium was extracted with acetone. After evaporation, the aqueous concentrate was adjusted to pH 3 and extracted with ethyl acetate. The extract was applied to preparative silica gel TLC plates, which was developed with hexaneethyl acetate-triethylamine (150:50:5). The crude material was subjected to HPLC (PEGASIL ODS, Senshu Scientific, Tokyo, Japan) with 87% methanol and 0.2% trifluoroacetic acid. The active fraction was further purified by XBridge C 18 HPLC (Waters, Milford, MA, USA) with 87% methanol and 0.2% triethylamine. The peak fraction was concentrated to dryness to give an orange powder of flaviogeranin (2.2 mg).The physicochemical properties of flaviogeranin are summarized as follows m.p. 160-165 1C; high-resolution FAB-MS m/z 371.1858 (MH + , calcd for C 22 H 27 O 5 , 371.1859); UV l max (e) 221 nm (252 000), 265 (125 000), 307 (64 200) and 429 (29 300) in methanol, 220 nm (250 000), 265 (125 000), 307 (64 000) and 429 (29 300) in 0.01 M HCl-methanol, 220 nm (sh, 246 000), 265 (109 000), 307 (59 500) and 429 (25 000) in 0.01 M NaOH-methanol; and IR (ATR) n max 3090, 3060, 1680 and 1630 per cm.The molecular formula of flaviogeranin was established as C 22 H 26 O 5 by high-resolution FAB-MS. The 13 C-and 1 H-NMR data for flaviogeranin are summarized in Table 1. All one-bond 1 H-13 C connectivities were confirmed by an HMQC 5 experiment. The HMBC 6 spectrum identified a naphthoquinone chromophore as shown in Figure 2. Long-range correlations from a phenolic hydroxyl (5-OH) to C-4a, C-5 and C-6 and from a singlet methyl (9-H 3 ) to C-5, C-6 and C-7 revealed the sequence of four aromatic carbons (C-4a, C-5, C-6 and C...

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