Yokonolide B (YkB; also known as A82548A), a spiroketal-macrolide, was isolated from Streptomyces diastatochromogenes B59 in a screen for inhibitors of ␤-glucoronidase expression under the control of an auxin-responsive promoter in Arabidopsis. YkB inhibits the expression of auxin-inducible genes as shown using native and synthetic auxin promoters as well as using expression profiling of 8,300 Arabidopsis gene probes but does not affect expression of an abscisic acid-and a gibberellin A 3 -inducible gene. The mechanism of action of YkB is to block AUX/IAA protein degradation; however, YkB is not a general proteasome inhibitor. YkB blocks auxin-dependent cell division and auxin-regulated epinastic growth mediated by auxin-binding protein 1. Gain of function mutants such as shy2-2, slr1, and axr2-1 encoding AUX/IAA transcriptional repressors and loss of function mutants encoding components of the ubiquitin-proteolytic pathway such as axr1-3 and tir1-1, which display increased AUX/IAAs protein stability, are less sensitive to YkB, although axr1 and tir1 mutants were sensitive to MG132, a general proteasome inhibitor, consistent with a site of action downstream of AXR1 and TIR. YkB-treated seedlings displayed similar phenotypes as dominant AUX/IAA mutants. Taken together, these results indicate that YkB acts to block AUX/IAA protein degradation upstream of AXR and TIR, links a shared element upstream of AUX/IAA protein stability to auxin-induced cell division/elongation and to auxin-binding protein 1, and provides a new tool to dissect auxin signal transduction.Auxin controls cell division, elongation, and differentiation and therefore, through its action at the level of the cell, exerts profound effects on growth and development throughout the life of the plant (1). Consistent with the diverse effects of auxin on growth and development is that the expression patterns of a number of genes are dramatically and rapidly altered by auxin application (2), suggesting that auxin ultimately regulates cell growth by controlling the profile of expressed genes. AUX/IAA genes comprise a 34-member gene family in Arabidopsis that is one of three known gene families that are regulated by auxin and implicated to play essential roles in auxin signaling (3, 4).The molecular and genetic studies on auxin signaling have revealed that auxin specifically enhances the transcription of many AUX/IAA genes within minutes without requiring de novo protein synthesis, suggesting that AUX/IAA genes are primary auxin-response genes (5, 6). AUX/IAA genes encode short lived nuclear proteins capable of heterodimerization with auxin-responsive factors (7) and are thought to act by negatively regulating the expression of early auxin-responsive genes including other members of the AUX/IAA family (3).Studies on Arabidopsis mutants with altered responses to auxin such as iaa3/shy2-2, iaa7/axr2-1, iaa17/axr3, iaa14/slr1, tir1, and axr1 revealed that the turnover rate of AUX/IAA proteins is in some way important in various developmental processes including ...

The conversion of quinolinic acid (QA) into a fluorescent compound by the catalytic activity of horseradish peroxidase (HRP) was investigated in the presence of hydrogen peroxide without exposure to light. Nonfluorescent quinolinic acid was converted into a fluorescent compound with maximum excitation and emission wavelengths at 328 and 377 nm, respectively. This fluorescent derivatization reaction with HRP in the presence of hydrogen peroxide was adopted for the determination of trace amounts of QA. The calibration curve obtained was linear from 0.1 to 5.0 nmol of QA in a 1.0 ml sample solution. The detection limit was 0.04 nmol/ml. The relative standard deviation at 3.0 nmol of QA was 3.58% (n = 8). This method was applied to the determination of QA spiked in control serum I and II. The recovery rates of QA were greater than 98%, and satisfactory results were obtained for both control serum I and II.

Hairy roots of goldenrod (Solidago altissima L.) were induced by infecting axenic plants with Agrobacterium rhizogenes strain A4. Growth and allelopathic polyacetylene (cis-dehydromatricaria ester, cis-DME) production of two independent hairy root clones were examined in several culture media and light regimes. cis-DME contents in hairy roots were at the same level as those in normal roots. cis-DME production in root cultures was several-fold lower than that of native plants and greatly repressed by light.

An iron(III) complex of thiacalix [4]arenetetrasulfonate attached to an anion-exchanger (Fe 3+ -TCASA-500) showed high peroxidase-like catalytic activity at pH 5 -8 for the formation of quinoid dye, following the color reaction between 3-methyl-2-benzothiazolinone hydrazone aniline (ALPS) in the presence of H2O2. This catalytic activity of Fe 3+ -TCASA-500 for the MBTH-ALPS system was applied for the spectrophotometric determination of H2O2, glucose, uric acid, and cholesterol. The calibration curves were linear in the concentration range from 1.0 to 15 μg of H2O2 in a 1.0-mL sample solution, and from 5.0 to 60 μg of glucose, 2.0 to 30 μg of uric acid, and 11.6 to 116 μg of cholesterol in a 0.5-mL sample solution. The apparent molar absorptivity of H2O2 was determined as 2.31 × 10 4 L mol -1 cm -1, which was about 70% of that by peroxidase under the same conditions. The determination method using Fe 3+ -TCASA-500 was applied for the determination of glucose and uric acid in both control sera I and II.

The fluorescent derivatization of tryptophan metabolites (xanthurenic acid, nicotinic acid, picolinic acid, and 3-hydroxyanthranilic acid) by the catalytic activity of horseradish peroxidase (HRP) was investigated in the presence of excess H2O2. Non-fluorescent xanthurenic acid (XA) and nicotinic acid (NA) were converted into a fluorescent compound with maximum excitation and emission wavelengths at 325 and 425 nm, and 318 and 380 nm, respectively. This fluorescent derivatization was developed for the fluorometric determination of trace amounts of XA and NA. The calibration curves were linear from 1.0 to 10.0 nmol XA and from 5.0 to 20.0 nmol NA in a 1.0-mL sample solution. The UV spectra of the reaction solutions suggested that compound III as an intermediate of HRP played an essential role in this fluorescent derivatization with HRP.