Auxin herbicides induce H(2)O(2) overproduction and tissue damage in cleavers (Galium aparine L.).
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The phytotoxic effects of auxin herbicides, including the quinoline carboxylic acids quinmerac and quinclorac, the benzoic acid dicamba and the pyridine carboxylic acid picloram, were studied in relation to changes in phytohormonal ethylene and abscisic acid (ABA) levels and the production of H(2)O(2) in cleavers (Galium aparine). When plants were root-treated with 10 microM quinmerac, ethylene synthesis was stimulated in the shoot tissue, accompanied by increases in immunoreactive levels of ABA and its precursor xanthoxal. It has been demonstrated that auxin herbicide-stimulated ethylene triggers ABA biosynthesis. The time-course and dose-response of ABA accumulation closely correlated with reductions in stomatal aperture and CO(2) assimilation and increased levels of hydrogen peroxide (H(2)O(2)), deoxyribonuclease (DNase) activity and chlorophyll loss. The latter parameters were used as sensitive indicators for the progression of tissue damage. On a shoot dry weight basis, DNase activity and H(2)O(2) levels increased up to 3-fold, relative to the control. Corresponding effects were obtained using auxin herbicides from the other chemical classes or when ABA was applied exogenously. It is hypothesized, that auxin herbicides stimulate H(2)O(2) generation which contributes to the induction of cell death in Galium leaves. This overproduction of H(2)O(2) could be triggered by the decline of photosynthetic activity, due to ABA-mediated stomatal closure. (+info)
Regulation of the gravitropic response and ethylene biosynthesis in gravistimulated snapdragon spikes by calcium chelators and ethylene inhibitors.
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The possible involvement of Ca2+ as a second messenger in snapdragon (Antirrhinum majus L.) shoot gravitropism, as well as the role of ethylene in this bending response, were analyzed in terms of stem curvature and gravity-induced asymmetric ethylene production rates, ethylene-related metabolites, and invertase activity across the stem. Application of Ca2+ chelators (ethylenediaminetetraacetic acid, trans-1,2-cyclohexane dinitro-N,N,N',N'-tetraacetic acid, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid) or a Ca2+ antagonist (LaCl3) to the spikes caused a significant loss of their gravitropic response following horizontal placement. Conversely, the Ca2+ ionophore A23187 or the agonist Bay K-8644 increased gravibending. Longitudinally halved stem sections had significantly higher amounts of ethylene, 1-aminocyclopropane-1-carboxylic acid, and 1-(malonylamino) cyclopropane-1-carboxylic acid compared with vertical controls, with the extra production arising exclusively from the lower half of the stem. trans-1,2-cyclohexane dinitro-N,N,N',N'-tetraacetic acid pretreatment completely abolished the gravity-induced ethylene gradient across the stem, thereby leading to a significant reduction of the curvature. Similarly, reduction of the ethylene produced in the gravistimulated with CoCl2 or inhibition of its action by silver thiosulfate or 2,5-norbornadiene significantly inhibited the subsequent gravibending. Silver thiosulfate and CoCl2 also abolished the gravity-induced gradient of invertase activity across the stem, which is associated with the asymmetric stem elongation. These results suggest that cytosolic Ca2+ may regulate auxin action in snapdragon spikes, manifested as increased ethylene production, which is, in turn, intimately correlated with stem bending. Therefore, both hormones seem to play significant roles in induction and progress of the gravibending of snapdragon spikes. (+info)
The role of gravity in apical dominance: effects of clinostating on shoot inversion-induced ethylene production, shoot elongation and lateral bud growth.
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Shoot inversion-induced release of apical dominance in Pharbitis nil is inhibited by rotating the plant at 0.42 revolutions per minute in a vertical plane perpendicular to the axis of rotation of a horizontal clinostat. Clinostating prevented lateral bud outgrowth, apparently by negating the restriction of the shoot elongation via reduction of ethylene production in the inverted shoot. Radial stem expansion was also decreased. Data from experiments with intact tissue and isolated segments indicated that shoot-inversion stimulates ethylene production by increasing the activity of 1-aminocyclopropane-1-carboxylic acid synthase. The results support the hypothesis that shoot inversion-induced release of apical dominance in Pharbitis nil is due to gravity stress and is mediated by ethylene-induced retardation of the elongation of the inverted shoot. (+info)
Evaluation of ethylene as a mediator of gravitropism by tomato hypocotyls.
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Assessments of the participation of ethylene in gravitropism by hypocotyls of tomato (Lycopersicon esculentum Mill.) indicate that gravitropism can occur without substantial change in ethylene production. Moreover, lowering or evaluating ethylene over a considerable range, as well as inhibiting ethylene action, fails to influence gravitropic bending. This vitiates the possibility that ethylene is a mediator of the primary, negative gravitropic response of tomato shoots. (+info)
Burst of ethylene upon horizontal placement of tomato seedlings.
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Seedlings of Lycopersicon esculentum Mill. cv Rutgers emit a pulse of ethylene during the first 2 to 4 minutes following horizontal placement. Because this burst appears too rapid and brief to be mediated by increase in net activity of 1-aminocyclopropane-1-carboxylic acid synthase, it might result form accelerated transformation of vacuolar 1-aminocyclopropane-1-carboxylic acid to ethylene. (+info)
Solid-state conformation of a hybrid tripeptide between beta-amino acid; 8-aminocyclooct-4-enecarboxylic acid and 2-aminoisobutyric acid.
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An eight-membered cyclic beta-amino acid, 8-aminocyclooct-4-enecarboxylic acid, was designed as a conformationally restricted non-proteinogenic amino acid. A hybrid tripeptide containing this eight-membered cyclic beta-amino acid and 2-aminoisobutyric acids was synthesized by conventional solution methods. The conformation of the tripeptide was studied using X-ray analysis and was shown to form an eleven-membered hydrogen-bonded turn (3(11)-helical structure) in the solid state. (+info)
Characterization of uptake and compartmentalization of 3,5,3'-tri-iodothyronine in cultured neonatal rat cardiomyocytes.
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The uptake of tri-iodothyronine (T(3)) in cultured neonatal rat cardiomyocytes was investigated and compared with the uptake of reverse T(3 )(rT(3)) and thyroxine (T(4)). Cellular compartmentalization of T(3) was studied by distinguishing T(3) activity associated with the plasma membrane from that in the cytosol or incorporated in the cell nucleus. T(3) and T(4) uptake displayed similar temperature dependencies which, in magnitude, differed from that of rT(3) uptake. T(3) uptake was Na(+ )independent, and sensitive to oligomycin and monodansylcadaverine (42-49% and 25% inhibition of 15-min cellular uptake respectively). Furthermore, T(3) uptake could be inhibited by tryptophan (20%) and tyrosine (12%), while 2-aminobicyclo[2,2,1]heptane-carboxylic acid had no effect. Co-incubation with tryptophan and oligomycin resulted in an additive inhibition of T(3) uptake (77%). We therefore conclude that (i) T(3) uptake is energy dependent, (ii) receptor-mediated endocytosis may be involved and (iii) the aromatic amino acid transport system T may play a role, while system L is not involved in T(3) transport in cardiomyocytes. Co-incubation with unlabeled iodothyronines showed that 3,3'-di-iodothyronine and T(3) itself were the most effective inhibitors of T(3) uptake (30% and 36% inhibition of 15-min cellular uptake respectively). At 15-min incubation time, 38% of the total cell-associated T(3) was present in the cytosol and nucleus, and 62% remained associated to the plasma membrane. Unidirectional uptake rates did not saturate over a free T(3) concentration range up to 3.9 microM. We have concluded that T(3) uptake in neonatal rat cardiomyocytes occurs by an energy- and temperature-dependent mechanism that may include endocytosis and amino acid transport system T, and is not sensitive to the Na(+) gradient. Elucidation of the molecular basis for the T(3) transporter is the subject of current investigation. (+info)
Susceptibility to the sugar beet cyst nematode is modulated by ethylene signal transduction in Arabidopsis thaliana.
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Previously, we identified Arabidopsis thaliana mutant rhd1-4 as hypersusceptible to the sugar beet cyst nematode Heterodera schachtii. We assessed rhd1-4 as well as two other rhd1 alleles and found that each exhibited, in addition to H. schachtii hypersusceptibility, decreased root length, increased root hair length and density, and deformation of the root epidermal cells compared with wild-type A. thaliana ecotype Columbia (Col-0). Treatment of rhd1-4 and Col-0 with the ethylene inhibitors 2-aminoethoxyvinylglycine and silver nitrate and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid suggests that the rhd1-4 hypersusceptibility and root morphology phenotypes are the result of an increased ethylene response. Assessment of known ethylene mutants further support the finding that ethylene plays a role in mediating A. thaliana susceptibility to H. schachtii because mutants that overproduce ethylene (eto1-1, eto2, and eto3) are hypersusceptible to H. schachtii and mutants that are ethylene-insensitive (etr1-1, ein2-1, ein3-1, eir1-1, and axr2) are less susceptible to H. schachtii. Because the ethylene mutants tested show altered susceptibility and altered root hair density and length, a discrimination between the effects of altered ethylene signal transduction and root hair density on susceptibility was accomplished by analyzing the ttg and gl2 mutants, which produce ectopic root hairs that result in greatly increased root hair densities while maintaining normal ethylene signal transduction. The observed normal susceptibilities to H. schachtii of ttg and g12 indicate that increased root hair density, per se, does not cause hypersusceptibility. Furthermore, the results of nematode attraction assays suggest that the hypersusceptibility of rhd1-4 and the ethylene-overproducing mutant eto3 may be the result of increased attraction of H. schachtii-infective juveniles to root exudates of these plants. Our findings indicate that rhd1 is altered in its ethylene response and that ethylene signal transduction positively influences plant susceptibility to cyst nematodes. (+info)