AO Activity Research Articles

The Effectiveness of the AOSpine Project of Education in Research: Changing Paradigms, Provoking Ideas, and Innovating the Mindful Practice

Introduction The way to increase innovation in mindful practice in a region without a culture in scientific investigation is through implementation of the Research Curriculum that is based on the competencies and learning outcome. No institutions have a Research Curriculum based on competence and learning outcome as guide to improve knowledge in research. The objective of this study is to describe the effectiveness of the project of education in research and the way to deliver this information effectively to those who aim to further improve their knowledge and participation in research. Materials and Methods the AO Research Curriculum uses the competency-based approach that aligns the following four components: (1) knowledge in research, (2) performing research, (3) specialized technical professional support, and (4) assessment to identify needs and track progress. The content of the curriculum was delivered using the most appropriate learning methods and techniques from the following four perspectives: (1) e-learning methods, (2) specific research symposiums, (3) precourses before AO activities, or as (4) specific lectures and structural presentations within the course, symposiums, or seminars. Research mentoring projects and joint publications are an objective way to measure the effectiveness of the project, as it represents the capacity to perform research. This protocol was applied in spine surgeons and university students. Results The survey of AOSpine Latin America members showed a low level of knowledge regarding research combined with a high motivation to learn. The organized competences, learning outcomes, and syllabus of the knowledge in Research promoted active learning and engagement of the members during AOSpine activities. These activities resulted in an increased membership, the participants were grateful when they understood the usefulness of research, and it was the best way to expand the AO product at the University, not only in the undergraduate courses, but also at the postgraduate levels as learning about tools in research and needs are the same for several areas (medicine, nursing, engineering, biology, and law). Conclusion The education in research project showed to be effective. The learning outcomes gained by the participants following completion of this project were recognized concerning where and how they can best obtain reliable information, perform a critical literature review, choose validated instruments to measure the patient's disease, obtain reliable feedback regarding the effectiveness of our surgical activity, and achieve a better understanding of the positive influence of the research on the medical routine. The “publication of results” is only a consequence of an attitude toward scientific investigation.

Abscisic acid and aldehyde oxidase activity in maize ear leaf and grain relative to post-flowering photosynthetic capacity and grain-filling rate under different water/nitrogen treatments

This study investigated changes in leaf abscisic acid (ABA) concentrations and grain ABA concentrations in two maize cultivars and analyzed the following relationships under different water/nitrogen treatments: leaf ABA concentrations and photosynthetic parameters; leaf ABA concentrations and grain ABA concentrations; leaf/grain ABA concentrations and grain-filling parameters; and aldehyde oxidase (AO,EC 1.2.3.1) activities and ABA concentrations. The ear leaf average AO activities and ABA concentrations were lower in the controlled release urea treatments compared with the conventional urea treatments. The average AO activities in the grains were higher in the controlled release urea treatments, and the ABA concentrations were significantly increased at 11-30 DAF. The Pn and ABA concentrations in ear leaves were negatively correlated. And the Gmean were positively correlated with the grain ABA concentrations at 11-30 DAF and negatively correlated with the leaf ABA concentrations at 20 and 40-50 DAF. The grain ABA concentrations and leaf ABA concentrations were positively correlated. Thus, the Gmean were closely related to the AO activities and to the ear leaf and grain ABA concentrations. As compared to other treatments, the subsoiling and controlled release urea treatment promoted the uptake of water and nitrogen by maize, increased the photosynthetic capacity of the ear leaves, increased the grain-filling rate, and improved the movement of photosynthetic assimilates toward the developing grains. In the cultivar Z958, higher ABA concentrations in grains at 11-30 DAF and lower ABA concentrations in ear leaves during the late grain-filling stage, resulted in higher grain-filling rate and increased accumulation of photosynthetic products (relative to the cultivar D3).

Antioxidant activity of propolis extracts from Serbia: A polarographic approach

Antioxidant activity (AO) of commercial propolis extracts (PEs), available on Serbian market, was determined by direct current (DC) polarography. Polarographic anodic current of 5.0mmolL−1 alkaline solution of H2O2 was recorded at potentials of mercury dissolution. Decrease of the current was plotted against the volume of gradually added PEs. The volume of PE causing 20% current decrease was determined from the linear part of the plot. Antioxidant activity was expressed in H2O2 equivalent (HPEq), representing the volume of PE that corresponds to 1.0mmolL−1 H2O2 decrease. Resulting HPEq ranged between 1.71±0.11 and 8.00±0.18μL. Range of 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity was from 0.093±0.004% to 0.346±0.006%. Total phenolic content (TCP) of PE with superior AO activity was 5.31±0.05%g GAE, while the extract with the lowest activity contained 1.45±0.02%g GAE. Antioxidant activity, determined by polarographic method, was correlated with DPPH scavenging activity (R2=0.991) and TCP (R2=0.985). Validity of obtained results was further confirmed using ANOVA and post hoc Tukey HSD test.

Cold‐Pressed Pumpkin Seed Oil Antioxidant Activity as Determined by a DC Polarographic Assay Based on Hydrogen Peroxide Scavenge

AbstractAntioxidant (AO) activity of cold pressed pumpkin (Cucurbita pepo L.) seed oil, produced from three naked and one hulled variety, was assessed using a DC polarographic assay based on a hydrogen peroxide scavenge (HPS). Results are expressed as the decrease of the anodic oxidation current of hydrogen peroxide obtained upon addition of methanolic extract of the investigated oils. Strict correlations of HPS and (1) radical scavenging capacity against the stable free radical 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) (0.99), (2) the induction period estimated by a Rancimat test (0.99) and (3) total phenolic content estimated by Folin‐Ciocalteu (FC) assay (0.99) were obtained. In addition, a significant correlation of HPS and the content of δ‐tocopherol (0.87), squalene (0.67) and color CIE a* (−0.89) was found. Based on the results reported, the polarographic assay was found to be suitable for determination of AO activity as an indicator of the quality and oxidative stability of oil.

Antioxidant and semicarbazide-sensitive amine oxidase inhibitory activities of glucuronic acid hydroxamate

The antioxidant and inhibitory activities of glucuronic acid (GluA) and its synthesized 1-methoxyl-6-glucuronic acid hydroxamate (GluA-NHOH) against semicarbazide-sensitive amine oxidase (SSAO) were investigated. The scavenging activities of GluA-NHOH against 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radicals (half-inhibition concentration [IC50], 152μM) and hydroxyl radicals (IC50, 70nM) were determined. The protective activities of GluA-NHOH against hydroxyl radical-mediated calf thymus DNA damage and peroxynitrite-mediated dihydrorhodamine oxidation were also investigated. GluA-NHOH, but not GluA, exhibited dose-dependent protective activities. GluA-NHOH, but not GluA, effectively inhibited bovine SSAO activities in a dose-dependent manner, and was further confirmed by AO activity stains on an acrylamide gel. GluA-NHOH showed mixed noncompetitive inhibition of bovine SSAO with respect to benzylamine (substrate) and benzylamine-SSAO (substrate–enzyme complex). The Vmax′ and Km′ values were reduced in the presence of GluA-NHOH (0.04mM).

The activity pattern and gene expression profile of aldehyde oxidase during the development of Pisum sativum seeds

Aldehyde oxidase (AO, EC 1.2.3.1) is a molybdenohydroxylase that is considered to catalyze the final step in the synthesis of abscisic acid (ABA) and possibly of indole-3-acetic acid (IAA). Five AO activity bands were detected after native PAGE with indole-3-aldehyde (PsAO-α, -β, -γ, -δ, -κ) and three with abscisic aldehyde (PsAO-γ, -δ, -κ) in developing seeds of Pisum sativum. At early and mid-development, PsAO-α, -β, -γ and only PsAO-γ were observed, respectively, and their localization as well as the expression of PsAOs genes was almost exclusively restricted to the maternal fruit tissues, the seed coat and pericarp. Towards the end of rapid reserve synthesis, two additional isoforms (PsAO-δ, -κ) appeared in cotyledons, coinciding with a high transcript level of PsAO2. At this developmental stage, the activity level of PsAO-γ, was still considerable in the testa, and was higher than at earlier stages in the embryonic axis, which correlated with the PsAO3 transcript level. In mature dry seeds, AO activity and the expression of PsAOs became restricted to the embryonic tissues. The possible involvement of AO isoforms in ABA or IAA synthesis during pea seed development as well as the contribution of particular PsAO genes to the formation of the dimeric pea AO isoforms is discussed.

Oxidative enzymes in tissues of the catfish (Clarias gariepinus) exposed to varying levels of cadmium

The activities of some oxidative enzymes (aldehyde oxidase, AO, EC 1.2.3.1; xanthine oxidase, XO, EC 1.17.3.2; sulphite oxidase, SO, EC 1.8.3.1; and monoamine oxidase, MO, EC 1.4.3.4) were investigated in the liver, gill, kidney, brain and muscle of a variety of African catfish (Clarias gariepinus) after 7 and 21 days of exposure to 0.1, 0.2 and 0.4 ppm cadmium (Cd) in ambient water. MO, SO and AO activities were significantly (p < 0.05) decreased in a dose-dependent manner in the liver, kidney and gill in the 7-day Cd-exposed fish when compared to control. Conversely, brain MO, AO and SO activities were significantly (p < 0.05) elevated in a dose-dependent manner in the same fishes relative to control. As in the 7-day Cd-exposed fish, the activities of MO, AO and SO were significantly (p < 0.05) decreased in a dose-dependent manner in the gill, kidney and liver of catfish exposed for 21 days. Same is true for XO in these organs after both duration of exposure, except in the liver where no significant change was observed relative to control. The inhibition of these oxidative enzymes in the liver, gill and kidney of catfish may interfere with their biotransformation function, and ultimately the survival of the fish may be compromised.

Troglitazone Thiol Adduct Formation in Human Liver Microsomes: Enzyme Knietics and Reaction Phenotyping

Troglitazone (TGZ) induced hepatotoxicity has been linked to cytochrome P450 (CYP)-catalyzed reactive metabolite formation. Therefore, the kinetics and CYP specificity of reactive metabolite formation were studied using dansyl glutathione (dGSH) as a trapping agent after incubation of TGZ with human liver microsomes (HLM) and recombinant human CYP proteins. CYP2C8 exhibited the highest rate of TGZ adduct (TGZ-dGS) formation, followed by CYP3A4, CYP3A5, and CYP2C19. The involvement of CYP2C8 and CYP3A4 was confirmed with CYP form-selective chemical inhibitors. The impact of TGZ concentration on the rate of TGZ-dGS formation was also evaluated. In this instance, two distinctly different profiles were observed with recombinant CYP3A4 and CYP2C8. It is concluded that both CYP3A4/5 and CYP2C8 play a major role in the formation of TGZ adduct in HLM. However, the contribution of these CYPs varies depending on their relative expression and the concentration of TGZ.

Aspergillus oryzae 또는 Bacillus natto 발효콩의 Isoflavone 함량과 생리활성

본 연구에서는 Asp. oryzae 및 B. natto로 각각 발효시킨 콩의 이소플라본의 함량변화, 생리활성에 대하여 비교, 조사하였다. 총 이소플라본 함량은 비발효콩이 81.80 ㎎/100 g, Asp. oryzae 발효콩이 130.70 ㎎/100 g, B. natto 발효콩이 139.50 ㎎/100 g이었다. 비발효콩, Asp. oryzae 발효콩 및 B. natto 발효콩의 총 페놀 함량은 각각 2.1, 4.3 및 7.6%이었고, 아질산염소거능은 각각 34.2, 55.2 및 92.5%로 측정되었다. 항균효과의 경우, B. natto 발효콩은 Staphylococcus aureus, Bacillus cereus와 Escherichia coli에서 가장 강한 항균효과가 나타났다. Asp. oryzae 발효콩은 Staphylococcus aureus와 Salmonella Enteritidis에서 항균효과를 보였다. 전체적으로 B. natto 발효콩의 항균성이 강하였다. SOD 유사활성은 Asp. oryzae 발효콩에서 가장 강했던 반면, 전자공여능에서는 B. natto 발효콩에서 가장 강한 radical 소거능이 측정되었다. 리놀레산 기질에 대한 Asp. oryzae 발효콩의 항산화 효과는 비발효콩이나 B. natto보다 큰 것으로 나타났으나, 유의적인 차이는 없었다.

Quantitative antioxidant activity of the ethylacetate extract of Larix sibirica bark and its individual components

The antioxidant [AO] properties of the ethylacetate extract of Larix sibirica bark and the flavonoids quercetin and dihydroquercetin found in it were studied using a model radical-chain oxidation of propan-2-ol in the kinetic regime. The quantitative characteristics of their AO activity were determined as effective rate constants fkln. It was found that dihydroquercetin had the highest AO activity among the studied natural compounds.

The plant Mo‐hydroxylases aldehyde oxidase and xanthine dehydrogenase have distinct reactive oxygen species signatures and are induced by drought and abscisic acid

The plant molybdenum-cofactor (Moco) and flavin-containing enzymes, xanthine dehydrogenase (XDH; EC 1.2.1.37) and aldehyde oxidase (AO; EC 1.2.3.1) are thought to play important metabolic roles in purine metabolism and hormone biosynthesis, respectively. Their animal counterparts contribute to reactive oxygen species (ROS) production in numerous pathologies and here we examined these enzymes as potential sources of ROS in plants. Novel in-gel assay techniques and Moco sulfurase mutants, lacking a sulfur ligand in their Moco active center, were employed to demonstrate that the native tomato and Arabidopsis XDHs are capable of producing O, but not H2O2, while the animal counterpart was shown to produce both, O and H2O2. Superoxide production was dependent on Moco sulfuration when using hypoxanthine/xanthine but not NADH as substrates. The activity was inhibited by diphenylene iodonium (DPI), a suicide inhibitor of FAD containing enzymes. Analysis of XDH in an Arabidopsis Atxdh1 T-DNA insertion mutant and RNA interference lines revealed loss of O activity, providing direct molecular evidence that plant XDH generates superoxides. Contrary to XDH, AO activity produced only H2O2 dissimilar to native animal AO, that can produce O as well. Surprisingly, H2O2 accumulation was not sensitive to DPI. Plant ROS production and transcript levels of AO and XDH were rapidly upregulated by application of abscisic acid and in water-stressed leaves and roots. These results, supported by in vivo measurement of ROS accumulation, indicate that plant AO and XDH are possible novel sources for ROS increase during water stress.

Aldehyde Oxidase (AO) in the Root Nodules of Lupinus albus and Medicago truncatula: Identification of AO in Meristematic and Infection Zones

Phytohormones are involved in the organogenesis of legume root nodules. The source of the auxin indole-3-acetic acid (IAA) in nodules has not been clearly determined. We studied the enzyme aldehyde oxidase (AO; EC 1.2.3.1), that catalyzes the last step of IAA biosynthesis in plants, in the nodules of Lupinus albus and Medicago truncatula. Primordia and young lupin nodules and mature M. truncatula nodules showed AO activity bands after native polyacrylamide gel electrophoresis. Gel activity analyses using indole-3-aldehyde as substrate indicated that the nodules of white lupin and M. truncatula have the capability to synthesize IAA via the indole-3-pyruvic acid pathway. Immunolocalization and in situ hybridization experiments revealed that AO is preferentially expressed in the meristematic and the invasion zones in Medicago nodules and in the lateral meristematic zone of Lupinus nodules. High IAA immunolabeling was also detected in the meristematic and invasion zones. Low expression levels and no AO activity were detected in lupin Fix- nodules that displayed restricted growth and early senescence. We propose that local synthesis of IAA in the root nodule meristem and modulation of AO expression and activity are involved in regulation of nodule development.

A coupled spectrophotometric enzyme assay for the determination of pectin methylesterase activity and its inhibition by proteinaceous inhibitors

Pectin methylesterase (PME; EC 3.1.1.11) activities are widespread in bacteria, fungi, and plants. PME-mediated changes in cell wall pectin structure play important roles in plant development. Genome sequencing projects have revealed the existence of large PME multigene families in higher plants. Additional complexity for PME regulation arises from the presence of specific PME inhibitor proteins (PMEI) in plant cells. Several assay procedures for the determination of PME activity have been reported. However, previous protocols suffered from various limitations. Here we report a protocol for a coupled enzyme assay based on methanol oxidation via alcohol oxidase (AO; EC 1.1.3.13) and subsequent oxidation of formaldehyde by formaldehyde dehydrogenase (FDH; EC 1.2.1.3). This simple and robust assay allows the continuous monitoring of PME activity in the neutral pH range. Furthermore, as plant PMEIs do not interfer with AO and FDH activities, this assay is suitable for the characterization of the inhibition kinetics of PMEI.

Amine Oxidases and Tumors

The physiological function in living organisms of amine oxidases, is not completely established but is certainly related to the biogenic amines metabolism and therefore involved in essential processes such as the cell growth and differentiation. A correlation between degree of tumor malignancy and level of AO activity has been reported. The catalytic products of oxidative deamination of amines (hydrogen peroxide and aminoaldehyde) exert a cytotoxic effect and are considered cell growth inhibitors. The biogenic amines in same way could be considered in the cells as both poisons and protectors. A balance of oxidant and antioxidant enzymes appears to be very important in carcinogenesis and cell growth regulation.

Over-expression of ascorbate oxidase in the apoplast of transgenic tobacco results in altered ascorbate and glutathione redox states and increased sensitivity to ozone.

Transgenic tobacco ( Nicotiana tabacum L. cv. Xanthi) plants expressing cucumber ascorbate oxidase (EC.1.10.3.3) were used to examine the role of extracellular ascorbic acid in mediating tolerance to the ubiquitous air pollutant, ozone (O(3)). Three homozygous transgenic lines, chosen on the basis of a preliminary screen of AO activity in the leaves of 29 lines, revealed up to a 380-fold increase in AO activity, with expression predominantly associated with leaf cell walls. Over-expression of AO resulted in no change in the total ascorbate content recovered in apoplast washing fluid, but the redox state of ascorbate was reduced from 30% in wild-type leaves to below the threshold for detection in transgenic plants. Levels of ascorbic acid and glutathione in the symplast were not affected by AO over-expression, but the redox state of ascorbate was reduced, while that of glutathione was increased. AO over-expressing plants exposed to 100 nmol mol(-1) ozone for 7 h day(-1) exhibited a substantial increase in foliar injury, and a greater pollutant-induced reduction in both the light-saturated rate of CO(2) assimilation and the maximum in vivo rate of ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation, compared with wild-type plants. Transgenic plants also exhibited a greater decline in CO(2) assimilation rate when exposed to a brief ozone episode (300 nmol mol(-1) for 8 h). Stomatal conductance, hence O(3) uptake, was unaffected by AO over-expression. Our findings illustrate the important role played by ascorbate redox state and sub-cellular compartmentation in mediating the tolerance of plants to ozone-induced oxidative stress.

The absence of molybdenum cofactor sulfuration is the primary cause of the flacca phenotype in tomato plants.

The molybdenum cofactor (MoCo)-containing enzymes aldehyde oxidase (AO; EC 1.2.3.1) and xanthine dehydrogenase (XDH; EC 1.2.1.37) require for activity a sulfuration step that inserts a terminal sulfur ligand into the MoCo. The tomato flacca mutation was originally isolated as a wilty phenotype due to a lack of abscisic acid (ABA) that is related to simultaneous loss of AO and XDH activities. An expressed sequence tag candidate from tomato was selected on the basis of homology to sulfurases from animals, fungi and the recently isolated Arabidopsis genes LOS5/ABA3. The tomato homologue maps as a single gene to the bottom of chromosome 7, consistent with the genetic location of the flacca mutation. The structure of FLACCA shows a multidomain protein with an N-terminal NifS-like sulfurase domain; a mammal-specific intermediate section; and a C-terminus containing conserved motifs. Prominent among these are molybdopterin oxidoreductases and thioredoxin redox-active centre/iron-sulfur-binding region signatures which may be relevant to the specific sulfuration of MoCo. Indeed, the molecular analysis of flacca identifies the mutation in a highly conserved motif located in the C-terminus. Activity gel assays show that FLACCA is expressed throughout the plant. Transient and stable complementation of flacca and the Arabidopsis aba3 mutants with Aspergillus nidulans hxB and FLACCA yielded full, partial and tissue-specific types of Mo-hydroxylase activities. Restoration of activity in the root alone is sufficient to augment plant ABA content and rectify the wild-type phenotype. Thus the pleiotropic flacca phenotype is due to the loss of activity of enzymes requiring a sulfurated MoCo.

Activity staining of plasma amine oxidase after polyacrylamide gel electrophoresis and its application to natural inhibitor screening.

Plasma amine oxidase (plasma AO, EC 1.4.3.6) is a copper-containing AO which converts benzylamine (BZ) to benzaldehyde, generating hydrogen peroxide and ammonia. The peroxidase was used as an ancillary enzyme to couple hydrogen peroxide to 3-amino-9-ethylcarbazole (AEC) to achieve plasma AO activity after electrophoresis on native polyacrylamide gels. It was confirmed that plasma AO is inhibited by semicarbazide but neither by clorgyline nor by deprenyl. We also used plasma AO activity staining for the screening of natural inhibitors. This fast and sensitive method can be used in the process of plasma AO purification, characterization, and inhibitor screening.

Outcome quality in trauma surgery

Trauma surgery and orthopedic trauma surgery have been accompanied not only by internal quality assessment, but also by external quality assessment procedures right from the beginning. The reasons for these mechanisms were based on legal regulations of treatment of work-related accidents. In 1958, the Arbeitsgemeinschaft für Osteosynthese (Working Group on Osteosynthesis, AO group) was founded. The results of the AO's scientific activities built the basis of osteosyntheses. In 1988, legal regulations changed again in Germany. Since this reform of some important facets of public health care, each hospital or institution is committed to perform external and internal quality assessment. In addition, the introduction of a payment system based on diagnosis-related groups makes it necessary to install basic quality management systems within the next few years. This paper presents some well-established procedures, especially the diagnosis-related study in the whole district of Westphalia-Lippe. The aim of the study was a quality assessment of the treatment of intracapsular fractures of the collum of the femur. Problems in data analysis and interpretation are shown. Because of some grave problems, certain changes in the study design seem to be warranted. Despite these facts, however, we are convinced that we not only need this kind of quality assessment, but that we should try to expand these studies based on the experiences we gained.

Transport and accumulation rates of abscisic acid and aldehyde oxidase activity in Pisum sativum L. in response to suboptimal growth conditions

Pea plants (Pisum sativum L.) grown initially in nutrient solutions with adequate nitrogen supply (4 mM NO3-) were transferred to solutions containing salt (50 or 100 mM NaCl), ammonium (4 mM) or a low nitrogen supply (0.4 mM NO3-). No changes of abscisic acid (ABA) content were found in roots of stressed pea plants 9 d after the beginning of the treatments; however, accumulation of ABA in the leaves was observed. Old leaves accumulated ABA to a higher extent than young leaves. Accumulation of ABA in leaves of ammonium-fed plants and plants grown under low nitrogen supply occurred in the absence of both increased ABA xylem loading rate and enhanced aldehyde oxidase (AO, EC 1.2.3.1) activity in roots. Enhanced leaf AO activity was observed in all treatments, with the highest increase in old leaves. Among the three AO isoforms (AO-1, AO-2 and AO-3) detected in extracts of pea leaves, the lowest one AO-3 (highest mobility in the gel) correlated with ABA production and showed the highest increment in response to the treatments. The increase of AO activity detected in leaves after 2 weeks of stress application was less prominent than after 9 d, suggesting a transient enhancement of ABA production following the onset of stress. An increase of ABA xylem loading rate as well as AO root activity 4 d and 9 d after application of the treatments was observed only in salt-treated plants followed by a decrease after 14 d in 100 mM NaCl. Decreased cytokinin (trans-zeatin riboside) delivery rate into the xylem sap was observed in all treatments. The role of abscisic acid and cytokinins as positive and negative growth signals, as well as the involvement of root-generated ABA on ABA accumulation in leaves is discussed.

Transport and accumulation rates of abscisic acid and aldehyde oxidase activity in Pisum sativum L. in response to suboptimal growth conditions

Pea plants ( Pisum sativum L.) grown initially in nutrient solutions with adequate nitrogen supply (4 mM NO 3− ) were transferred to solutions containing salt (50 or 100 mM NaCl), ammonium (4 mM) or a low nitrogen supply (0.4 mM NO 3− ). No changes of abscisic acid (ABA) content were found in roots of stressed pea plants 9 d after the beginning of the treatments; however, accumulation of ABA in the leaves was observed. Old leaves accumulated ABA to a higher extent than young leaves. Accumulation of ABA in leaves of ammonium‐fed plants and plants grown under low nitrogen supply occurred in the absence of both increased ABA xylem loading rate and enhanced aldehyde oxidase (AO, EC 1.2.3.1) activity in roots. Enhanced leaf AO activity was observed in all treatments, with the highest increase in old leaves. Among the three AO isoforms (AO‐1, AO‐2 and AO‐3) detected in extracts of pea leaves, the lowest one AO‐3 (highest mobility in the gel) correlated with ABA production and showed the highest increment in response to the treatments. The increase of AO activity detected in leaves after 2 weeks of stress application was less prominent than after 9 d, suggesting a transient enhancement of ABA production following the onset of stress. An increase of ABA xylem loading rate as well as AO root activity 4 d and 9 d after application of the treatments was observed only in salt‐treated plants followed by a decrease after 14 d in 100 mM NaCl. Decreased cytokinin ( trans‐ zeatin riboside) delivery rate into the xylem sap was observed in all treatments. The role of abscisic acid and cytokinins as positive and negative growth signals, as well as the involvement of root‐generated ABA on ABA accumulation in leaves is discussed.