1,721,101 research outputs found
Flavonoid facilitated/passive transport: Characterization of quercetin microsomal uptake by a DPBA-dependent assay
No full textFree fatty acids dissipate proton electrochemical gradients in pea stem microsomes and submitochondrial particles
No full textThe effect of free fatty acids (FFA) and lysophosphatidylcholine-oleoyl (lyso-PC) on proton gradients of pea stem microsomes and submitochondrial particles was studied. Linolenic (18:3), linoleic (18:2), oleic (18:1), palmitic (16:0) and stearic (18:0) acids collapsed the proton gradient generated by addition of ATP or PP to microsomes. When an artificial ΔpH was generated by NaOH, FFA did not induce any effect, but the subsequent addition of valinomycin dissipated the proton gradient. FFA were also able to discharge the ΔpH built up by the oligomycin-sensitive H+-ATPase of submitochondrial particles and the electrical potential generated by NADH oxidation in intact mitochondria. Free fatty acids stimulated NADH-dependent oxygen consumption by mitochondria and this effect was not abolished by ADP or carboxyatractyloside (CAtr). The effect of FFA increased with an increasing unsaturation of the acyl chain, while the length of the chain did not influence the activity. Lysophosphatidylcholine dissipated the proton gradient generated by H+-PPase of microsomes and H+-ATPase of submitochondrial particles, while the H+-ATPase of microsomes was slightly affected. In addition, lyso-PC stimulated NADH-dependent oxygen uptake by mitochondria. Also in this case, neither ADP nor CAtr inhibited this stimulated O2 consumption. These results show that FFA uncoupled oxidative phosphorylation of pea mitochondria and collapsed only proton electrochemical gradients in pea microsomes and submitochondrial particles. Therefore, in this regard FFA are similar to artificial protonophores, acting as proton carriers. The mechanism of action of lyso-PC appears to be more complex and different possible explanations are proposed
Structural and functional properties of plant mitochondrial F-ATP synthase
Full text linkThe mitochondrial F-ATP synthase is responsible for coupling the transmembrane proton gradient, generated through the inner membrane by the electron transport chain, to the synthesis of ATP. This enzyme shares a basic architecture with the prokaryotic and chloroplast ones, since it is composed of a catalytic head (F1), located in the mitochondrial matrix, a membrane-bound part (FO), together with a central and a peripheral stalk. In this review we compare the structural and functional properties of F-ATP synthase in plant mitochondria with those of yeast and mammals. We also present the physiological impact of the alteration of F-ATP synthase in plants, with a special regard to its involvement in cytoplasmic male sterility. Furthermore, we show the involvement of this enzyme in plant stress responses. Finally, we discuss the role of F-ATP synthase in shaping the curvature of the mitochondrial inner membrane and in permeability transition pore formation
Ecophysiological response of maize (Zea mays L.) to water stress: remote sensing and upscaling techniques for a more efficient management of water resources in agriculture
Full text linkATP synthesis driven by α-keto acid-stimulated alternative oxidase in pea leaf mitochondria
No full textThe electrical potential difference (A¥) generation and
ATP synthesis due to a-ketoacid stimulated alternative oxidase activity in pea leaf mitochondria, energized by malateplus glutamate, was studied. In the absence of a-ketoacids, DF was ca. 60% collapsed by KCN or antimycin A (AA), while the remaining part (ca.30%was dissipated by salicylhydroxamicacid (SHAM). The presence of a-ketoacids
(pyruvate or iodoacetate),known to stimulate the alternative oxidase,caused a decrease in the KCN- or AA-sensitive component of A'F(ca.30%), which was accompanied by an increase in the SHAM-sensitive one. When mitochondria were energized by exogenous NADH, succinate or duroquinol, AY was completely collapsed by KCN or AA, either in the presence or absence of a-ketoacids. ADP partially collapsed the-sensitive component of AT, and oligomycin restored this dissipation. In the presence of pyruvate or iodoacetate, ATP content in KCN-treated mitochondria was ca.40 of control,while that in SHAM plus KCN-inhibited mitochondria was negligible. AOP stimulated oxygen uptake only in the presence of KCN(respiratory control ratio = 1.7), but not in the presence of KCN plus SHAM. It is concluded that a-ketoacids, stimulating the oxidation of NAD-linked substrates through the alternative oxidase, lead to an increase in the SHAM-sensitive component of zliP via complex I, thus increasing the contribution of this pathway to ATP synthesis when the cytochrome oxidase is restricted
Caspase-3-like activity and proteasome degradation in grapevine suspension cell cultures undergoing silver-induced programmed cell death
Full text linkToxic metal contamination is one of the major environmental concerns of the recent decade, due to the large application of metals in industrial, healthcare and commercial products, even in the form of nanostructures and nanomaterials. Nevertheless, the effects of silver (Ag+) on plants have not yet thoroughly elucidated. Therefore, suspension cell cultures of grapevine were used as a model for investigating silver toxicity. To do this, oxidative
stress and programmed cell death (PCD), evaluated as reactive oxygen species production, caspase-3-like activity and ubiquitin-proteasome system, were investigated.
As a result, the highest concentration (10 μM) of Ag+ caused a rapid (within 24 h) induction of PCD (approx. 80%), accompanied by generation of reactive oxygen species and activation of caspase-3-like activity. In the presence of specific inhibitor of this enzyme, a partial recovery of cell viability and a strong inhibition of caspase-
3-like activity was observed. In addition, silver-induced PCD was accompanied either by increase of poly-ubiquitin conjugated proteins and degradation of subunit PBA1 of the proteasome 20S core, similarly to what found for metal-induced neurotoxicity in animals.
The present study shows that silver could induce PCD in grapevine suspension cell cultures, mediated by caspase-3-like activity and oxidative stress. These effects were associated to accumulation of poly-ubiquitin conjugated proteins, suggesting the impairment of ubiquitin-proteasome complex, confirmed by the decrease of the PBA1 subunit. These findings indicate that animal and plant cells could share a common pathway in response
to toxic metal, which involves PCD and disassembling of proteasome complex
Plant mitochondrial electrical potential monitored by fluorescence quenching of rhodamine 123
No full textThe suitability of the fluorescent dye rhodamine 123 for qualitative and quantitative determinations of the electrical potential difference (ΔΨ) in isolated pea (Pisum sativum L.) stem mitochondria was evaluated. A fluorescence quenching of rhodamine 123, as a consequence of dye uptake, occurred following mitochondria energization by both external and internal substrates. This quenching was associated to the generation of ΔΨ, because it was completely released by uncouplers and respiratory inhibitors. The conversion of the proton gradient (ΔpH) into ΔΨ, induced by nigericin or a permeant weak acid (phosphate), increased the quenching. The uptake of the probe was accompanied by 40% of unspecific binding in coupled, but not in uncoupled, mitochondria. Rhodamine. 123 quenching varied linearly with a K+-diffusion potential. ADP induced a transient and cyclic change of fluorescence which was associated to ATP synthesis. Consequently, rhodamine 123 did not influence oxygen consumption by mitochondria in both state 4 and 3, thus indicating that, at the concentrations assayed, the probe was not toxic. It is concluded that rhodamine 123, followed by fluorescence quenching, is a suitable probe to study the energetics of isolated plant mitochondria
Effect of 6-ketocholestanol on FCCP- and DNP-induced uncoupling in plant mitochondria
No full textEffect of 6-ketocholestanol on FCCP-induced and DNP-induced uncoupling in beef liver and pea stem mitochondria was studied, under experimental conditions at which this steroid abolished the effect of low concentrations of FCCP and other most potent uncouplers in rat mitochondria [Starkov et al. (1994) FEBS Lett., 355, 305–308]. It is shown that, in both types of mitochondria, 6-ketocholestanol prevents or reverses the uncoupling induced by low concentrations of FCCP, but not that caused by high concentrations of FCCP or by any concentration of DNP. Progesterone and male sex hormones, showing recoupling capability in animal mitochondria, appear to be ineffective in the plant system. Cholesterol does not recouple in both animal and plant mitochondria. Plant steroids, such as β-sitosterol and stigmasterol, are also without effect
Lipoxygenase activity associated to isolated soybean plasma membranes
No full textHighly purified soybean (Glycine max L. Merr.) plasma membranes exhibit a lipoxygenase activity with a pH optimum in the acidic (5.5-6.0) range and with a K(m) value of 200 μM for both linolenic and linoleic acids. This activity is inhibited by nordihydroguaiaretic acid (NDGA), salicylhydroxamic acid (SHAM) and propyl gallate, stimulated by CaCl2, up to 0.25 mM, H2O2 (5 to 10 nM range) and by some nucleotide triphosphates (125 to 1000 nM range) in the following order ATP > GTP = UTP > CTP. The enzyme is not released by treatment of the membranes with 0.05% Brij 58 and its activity is approx. 65% inhibited by the impermeant p-chloromercuryphenyl-sulfonate only in 0.01% Triton X-100-treated membrane vesicles. These results indicate that soybean cells have an acid lipoxygenase, associated to the plasmalemma, with the catalytic site on the cytoplasmic surface. It may be distinguished from the soluble counterpart, because the latter is not stimulated by nucleotide triphosphates. The plasma membrane vesicles also show a lipoxygenase, active in the alkaline (9.0-9.5) range, inhibited by NDGA, SHAM and propyl gallate, stimulated by H2O2, but with a lower K(m) value (60 μM) and less sensitive to calcium stimulation than the acidic one. The possible involvement of acid lipoxygenase in senescence and in the response of plant cells to wounding and pathogen infection is discussed
Seed storage in polyethylene bags of a recalcitrant species (Quercus ilex L.): analysis of some bio-energetic and oxidative parameters.
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