IAA, a major form of auxin, is biosynthesized from l-tryptophan via the indole-3-pyruvic acid (IPyA) pathway in Arabidopsis. Tryptophan aminotransferases (TAA1/TARs) catalyze the first step from l-tryptophan to IPyA. In rice, the importance of TAA/TARs or YUC homologs in auxin biosynthesis has been suggested, but the enzymatic activities and involvement of the intermediate IPyA in auxin biosynthesis remain elusive. In this study, we obtained biochemical evidence that the rice tryptophan aminotransferase OsTAR1 converts l-tryptophan to IPyA, and has a Km of 82.02 µM and a Vmax of 10.92 µM min-1 m-1, comparable with those in Arabidopsis. Next, we screened for an effective inhibitor of OsTAR1 from our previously reported inhibitor library for TAA1/TARs, designated pyruvamine (PVM). Differing from previous observations in Arabidopsis, hydroxy-type PVMs, e.g. PVM2031 (previous name KOK2031), had stronger inhibitory effects in rice than the methoxy-type. PVM2031 inhibited recombinant OsTAR1 in vitro. The Ki of PVM2031 was 276 nM. PVM2031 treatment of rice seedlings resulted in morphological changes in vivo, such as reduced lateral root density. Exogenous IAA rescued this growth inhibition, suggesting that the inhibitory effect is auxin specific. Furthermore, rice roots showed reduced IAA levels concomitant with reduced levels of IPyA in the presence of the inhibitors, suggesting that the IPyA pathway is an auxin biosynthesis pathway in rice. Since PVM2031 showed stronger inhibitory effects on rice auxin biosynthesis than known tryptophan aminotransferase inhibitors, we propose that the hydroxy-type PVM2031 is an effective tool for biochemical analysis of the function of auxin biosynthesis in rice roots.
The behavior of dynamic recrystallization of pure nickel is investigated by uniaxial compression tests at temperatures and strain rates ranging from 873 K to 1573 K and from 2.5×10-5 s -1 to 1.0×10 -3 s -1 , respectively. The textures formed during dynamic recrystallization are investigated by calculating orientation distribution function. Orientation measurements of individual grains also carried out by EBSP technique. It was found that the texture varies depending on the value of Zener-Hollomon parameter (hereafter abbreviated as Z). At high Z conditions, area of high pole density is distributed from (011) to 10 degrees away from (011) to (001). No sharp textures were observed at low Z conditions. It was concluded that new grains were formed by strain-induced grain boundary migration at low Z conditions. During the migration, many twins are formed, resulting in no texture formation. The fraction of twin boundary varied depending on the value of Z, suggesting that dynamic recrystallization is available for grain boundary character distribution control.
The extraction kinetics of copper from aqueous ammonium nitrate-ammonia mixture with nhexane solution of Versatic acid was studied by the single-drop method. The change of extraction rate with concentrations of reactant species, such as copper and hydrogen ions in the continuous phase and Versatic acid in the dispersed phase, respectively, was studied for drop-formation and drop-rise periods.It became clear that the extraction rates during both periods were controlled only by the heterogeneous complex-forming reaction at the drop surface. The heterogeneous reaction rate was found to be proportional to the concentration of copper ion in the aqueous phase, inversely proportional to that of hydrogen ion and independent of that of Versatic acid in the dispersed phase. Fromthe dependency of the reaction rate on the concentration of each reactant species and from the experimental results on the inter facial adsorption properties of Versatic acid, the rate-controlling step of this complex-forming reaction at the drop surface is considered to be as follows.Cu2+ +R7d.-CuR+d..
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