Effect of exo-16,17-dihydro-gibberellin A5 on gibberellin A20 metabolism in seedlings of dwarf rice (Oryza sativa L. cv. Tan-ginbozu)

Several of the 16,17-dihydro gibberellins (GAs) inhibit elongation in a variety of species. In a study of their mechanism of action we have investigated the effect of exo-16,17-dihydro-Ga₅ (diHGA₅) on the metabolism of GA₂₀ in dwarf rice (Oryza sativa cv. Tan-ginbozu). A mixture of [³H]- and [³H]-GA₂₀ (100 ng per plant) was applied in microdrops to 4 d old seedlings which were harvested 72 h later. Concurrent treatment with diHGA₅ at 100 ng or 333 ng per plant reduced GA₂₀-induced elongation of the second leaf sheath by 41–66%. There was a concomitant reduction in the amount of [²H₂]GA₁ present at harvest, measured by gas chromatography-mass spectrometry-selected ion monitoring. The [²H₂]GA₂₉ content was also reduced. There was no clear effect of diHGA₅ on the total radioactivity recovered, or on conversion of the [³H]GA₂₀ to putative [³H]GA conjugates, or on the amount of [²H₂]GA₂₀ found. No free [²H₂]GA₈ was detected. In other experiments there was little effect of diHGA₅ on elongation induced by treatment with GA₁. We conclude that diHGA₅ inhibited GA₂₀-induced elongation in dwarf rice shoots at least partly by reducing the 3-hydroxylation of GA₂₀ to GA₁.Abbreviations diHGA₅ = exo- 16, 17-dihydro-gibberellin A₅ - GA = gibberellin - GC-MS-SIM = gas chromatography-mass spectrometry-selected ion monitoring     

Promotion of mesocotyl growth in etiolated rice seedlings by 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione

4-Ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione (TA) promoted mesocotyl growth in dark-grown rice (Oryza sativa L.) seedlings. In cultivars of the japonica type TA alone showed a small promotive effect and TA+gibberellic acid(GA₃) had a marked synergistic effect, while in other cultivars, mostly of the indica type, TA alone showed a great promotive effect and TA+GA₃ had only an additive effect. In cv. Nato, a typical representative of cultivars showing the second type of response, the concentration of TA giving the greatest growth promotion was around 0.1–0.2 mM. In Nato seedlings treated with TA at 0.1 mM, the mesocotyls continued to elongate for 6 days and reached about 75 mm in length, while the mesocotyls of control seedlings grew to a maximum of about 10 mm and growth was limited to the first 3 days after planting. The TA-induced mesocotyl elongation was mainly the consequence of increased cell multiplication in the meristematic area immediately below the coleoptilar node. GA₃, abscisic acid (ABA) and ethylene also stimulated mesocotyl growth in dark-grown Nato seedlings but their effects were much smaller than those of TA. ABA, like GA₃, had an additive effect with TA, but ethylene suppressed the effect of TA and resulted in increased lateral expansion in the upper region of the mesocotyls of TA-treated seedlings.Abbreviations ABA abscisic acid - GA(s) gibberellin(s) - GA₃ gibberellic acid - TA 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione Part 5 in the series Plant Growth-regulating Activities of Isourea Derivatives and Related Compounds; Part 4=Ogawa et al. (1978)     

Metal accumulation and damage in rice (cv. Vialone nano) seedlings exposed to cadmium

The effect of exposure to increasing cadmium concentrations was analyzed in rice seedlings (cv. Vialone nano). The highest Cd accumulation was found in roots, mostly in the apoplastic environment. Cd taken up in cells led to an increase in sulfhydryl groups, the appearance of phytochelatins, and formation of electron-dense vacuolar inclusions. The metal-exposure inhibited root growth and also interfered with correct root morphogenesis, causing disordered division and abnormal and forward enlargement of epidermal and cortical cell layers in the apical region. Cd accumulation in shoots was lower than in roots. In leaf cells, there was neither a substantial increase in sulfhydryl groups nor the appearance of phytochelatins. Shoot growth was reduced and, differently from in roots, leaf cell enlargement was inhibited. Chloroplasts had lowered contents of chlorophyll and a reduced number of thylakoids, but underwent structural alterations only at the highest Cd concentration tested (250 μM). Photosynthetic activity was limited due to the curtailment of CO₂ availability caused by the greater resistance of Cd-exposed leaves. The damage suffered by seedlings worsened with the increase in Cd concentration, but was already evident at the lowest concentration examined (50 μM), showing that the cv. Vialone nano has a Cd-sensitivity higher than other rice cultivars.     

Beta-Endorphin: lack of correlation between opiate activity and immunoreactivity by radioimmunoassay.

A sensitive radioimmunoassay for human β-endorphin has been developed. When natural human β-lipotropin and various synthetic analogs of β-endorphin were assayed for their immunoreactivity, lack of correlation was found between opiate activity and immunoreactivity. These data suggest that residues 6–15 of β-endorphin are the antigenic determinant.     

A synergistic effect of 2-ethyl-l-isopropoxycarbonyl-3-(4-tolylcarbamoyl) isourea with gibberellic acid on growth of rice seedlings

2-Ethyl-1-isopropoxycarbonyl-3-(4-tolylcarbamoyl)isourea [EITIU]stimulated both shoot and root growth of rice seedlings. Gibberellicacid [GA]-induced shoot elongation was further stimulated byEITIU, and the combined application of both compounds was shownto be distinctly synergistic. A similar synergistic action wasobserved in the growth of rice mesocotyls in the dark. The inhibitionof root growth caused by GA was overcome by combination withEITIU. The growth-stimulating activity of EITIU was not observedin lettuce hypocotyls. ¹ This paper is Part I in the series "Plant growth-regulatingactivities of isourea derivatives and related compounds." (Received February 7, 1976; )     

Synthesis of ent-17-(prop-1-ynyl-17 beta-hydroxy-11 beta-(4-(N,N-dimethylamino)-phenyl)-4,9-estradien-3-one, the antipode of RU-38 486

The title compound was synthesized and tested for its biological activities. It showed neither antiprogesterone nor antiglucocorticoid properties.     

Optimization of ammonium acquisition and metabolism by potassium in rice (Oryza sativa L. cv. IR-72)

We present the first characterization of K⁺ optimization of N uptake and metabolism in an NH₄⁺‐tolerant species, tropical lowland rice (cv. IR‐72). ¹³N radiotracing showed that increased K⁺ supply reduces futile NH₄⁺ cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux. Pharmacological testing showed that low‐affinity NH₄⁺ influx may be mediated by both K⁺ and non‐selective cation channels. Suppression of NH₄⁺ influx by K⁺ occurred within minutes of increasing K⁺ supply. Increased K⁺ reduced free [NH₄⁺] in roots and shoots by 50–75%. Plant biomass was maximized on 10 mm NH₄⁺ and 5 mm K⁺, with growth 160% higher than 10 mm NO₃^‐‐grown plants, and 220% higher than plants grown at 10 mm NH₄⁺ and 0.1 mm K⁺. Unlike in NH₄⁺‐sensitive barley, growth optimization was not attributed to a reduced energy cost of futile NH₄⁺ cycling at the plasma membrane. Activities of the key enzymes glutamine synthetase and phosphoenolpyruvate carboxylase (PEPC) were strongly stimulated by elevated K⁺, mirroring plant growth and protein content. Improved plant performance through optimization of K⁺ and NH₄⁺ is likely to be of substantial agronomic significance in the world's foremost crop species.     

The in vivo metabolism of 7 beta, 17-dimethyltestosterone-6,7-3H.

7 beta, 17-Dimethyltestosterone (17 beta-hydroxy-7 beta, 17-dimethyl-4-androsten-3-one) (I) was given to three subjects in oral doses of 400 mg per day for ten days. The initial dose contained the steroid tritiated in the 6 and 7 positions. Plasma levels and urinary excretion patterns were followed in all three subjects. Isolations were done on the urine, plasma, and stools of one patient. From the urine 7 beta, 17-dimethyl- 5 alpha-androstane-3 beta,17 beta-diol (VI) was isolated from the nonhydrolyzed fractions. Unchanged (I), 7 beta,17-dimethyl-5 beta-androstane-3 alpha,17 beta-diol (III) and 7 beta, 17-dimethyl-5 beta-androstane-3 beta,17 beta-diol (IV) were isolated from the nonhydrolyzed and enzyme-hydrolyzed fractions. 7 beta,17-dimethyl-5 alpha-androstane-3 alpha,17 beta-diol (V) was isolated from the enzymatic fractions. From the stools were isolated unchanged (I), (III), (IV), (V), and (VI). Unchanged (I) and its 5 alpha-dihydro derivative (17 beta-hydroxy-7 beta,17-dimethyl-5 alpha-androstan-3-one) (II) were identified in the plasma. The total recovery of radioactivity in the one patient on whom the isolations were done was 57%; 40% from the urine and 17% from the stools.     

A correlation between changes in gamma-aminobutyric acid metabolism and seizures induced by antivitamin B6.

The effects of DL-penicillamine (DL-PeA), hydrazine and toxopyrimidine (TXP, 2-methyl-6-amino-5-hydroxymethylpyrimidine) on gamma-aminobutyric acid (GABA) metabolism in mouse brain were studied. All these compounds inhibited the activity of glutamate decarboxylase [EC 4.1.1.15] (GAD) and slightly inhibited that of 4-aminobutyrate: 2-oxoglutarate aminotransferase [EC 2.6.1.19] (GABA-T). In contrast, very different effects were observed on GABA levels; hydrazine caused a marked increase, DL-PeA had no effect, and TXP caused a slight decrease in the content of the amino acid. These results could be described by an equation which related the excitable state to changes in the flux of the GABA bypass. Since the values obtained from the equation clearly reflect the seizure activity, it is suggested that the decreased GABA flux might be a cause of convulsions induced by these drugs.     

Studies of the inhibitory activity of MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-indol- 2-yl]-2,2-dimethyl propanoic acid) on arachidonic acid metabolism in human phagocytes.

We have investigated the inhibitory activity of compound MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-i ndol-2- yl]-2,2-dimethyl propanoic acid) on 5-lipoxygenase (5-LO) product synthesis in various human phagocytes stimulated with either the ionophore A23187, opsonized zymosan (OPZ), platelet-activating factor (PAF), or formyl-methionyl-leucyl-phenylalanine (fMLP). The lipoxygenase products were analyzed by reversed-phase HPLC. MK-0591 inhibited the formation of 5-hydroxyeicosatetraenoic acid, leukotriene (LT) B4, its omega-oxidation products, and 6-trans-isomers with IC50 values of 2.8-4.8 nM in A23187-stimulated neutrophils. In these conditions, arachidonic acid at a concentration of 10 microM had no effect on MK-0591 inhibitory activity. In neutrophils stimulated with OPZ, the synthesis of LTB4, its omega-oxidation products, and 6-trans-isomers was inhibited with IC50 values of 9.5-11.0 nM. MK-0591 inhibited 5-LO product synthesis in A23187-stimulated blood monocytes, eosinophils, and alveolar macrophages with IC50 values of 0.3-0.9, 3.7-5.3, and 8.5-17.3 nM, respectively. In neutrophils primed with granulocyte--macrophage colony-stimulating factor and stimulated with PAF, lipoxygenase product synthesis was inhibited with IC50 values of 7.7-8.7 nM. At the concentration of 1 microM, MK-0591 had no inhibitory effect on 15-lipoxygenase activity in human polymorphonuclear leukocytes, nor on human platelet 12-lipoxygenase and cyclooxygenase. In conclusion, MK-0591 is a very potent and specific inhibitor of 5-LO product synthesis in various types of human phagocytes.     

Hepatic metabolism of short-chain bile acids. Inversion of the 3-hydroxyl group of isoetianic acid (3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acid) by the adult rat

The stereospecificity of mechanisms for hepatic transport of short-chain bile acids has been examined by following the hepatic metabolism and biliary secretion of 3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acid (isoetianic acid) administered in two different labeled forms to rats prepared with an external biliary fistula. While 93% of the administered [2,2,4,4-3H]isoetianic acid was recovered in bile after 20 h, only 18% of a similar dose of [3 alpha-3H]isoetianic acid was secreted in bile over the same time period. The recovered radioactivity of the latter compound was mainly associated with bile water. With the [2,2,4,4-3H]isoetianic acid, the bulk of the biliary isotope was determined to be in the form of two glucuronide conjugates. Spectral analysis identified these metabolites as the hydroxyl-linked (major) and carboxyl-linked (minor) beta-glucuronides, not of the 3 beta-hydroxy compound administered, but of 3 alpha-hydroxy-5 beta-androstane-17 beta-carboxylic acid (etianic acid), i.e., the products of hydroxyl group inversion. It is concluded that isoetianic acid is efficiently cleared from plasma and conjugated with glucuronic acid after its epimerization to etianic acid. The prevalent, but not complete, loss of the 3-tritium atom and the retention of the 2- and 4-tritium atoms probably indicates a 3-oxo-5 beta-androstane-17 beta-carboxylic acid intermediate with partial return of the label via a limited labeled pool of reduced nicotinamide cofactor.