Peroxidase Patterns Research Articles

Changes in activities of antioxidant enzymes during Chenopodium murale seed germination

The activities and isoenzyme pattern of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) have been studied during germination of Chenopodium murale seeds. CAT and SOD activities were similar in dry seeds and during first 2 d of imbibition. CAT activity increased during radicle protrusion and early seedling development. The maximum SOD activity was found at final stages of germination and early seedling development. POD activity was not detected until the 6th day of germination, indicating POD involvement not until early seedling development. Gibberellic acid (GA3, 160 µM) delayed and synchronized C. murale germination.

Induction of PR proteins and resistance by the biocontrol agent Clonostachys rosea in wheat plants infected with Fusarium culmorum

Clonostachys rosea (CR) is a common worldwide saprophyte with destructive effect against several plant pathogenic fungi showing antagonistic features against a wide variety of pathogens. We recently isolated a strain of C. rosea, named CR47, from wheat crown infected with Fusarium culmorum (FC); this strain proved to be effective against Fusarium seed borne diseases of cereals under field condition. In this paper the function of C. rosea applied as seed treatment on wheat seedling growth was investigated. In addition, we investigated the expression pattern of peroxidases and chitinases as well as PR4 proteins following both CR treatments of seeds and FC infection and also in the three-component system pathogen–antagonist–wheat. Several chitinase isoforms were induced by CR-treatment both in coleoptiles and roots, whereas some peroxidase isoforms were induced only in the presence of both antagonist and pathogen. In the latter case, it seems that CR-treatment by itself promotes plant growth and reduces the peroxidase expression, while enhances some chitinase isoforms probably involved in cell wall disruption. Moreover, both the antagonist and the pathogen studied induced PR4 protein expression, which probably exerts its role on the invading microorganisms by a translation-inhibitory process that could be ascribed to their ribonuclease activity.

Comparison of Protein Profile and Peroxidases in Bush and Vine-type Tropical Pumpkin

Comparisons of total peroxidase activity and peroxidase isozymes as well as protein profiles among segregating, near-isogenic bush and vine phenotypes of pumpkin (Cucurbita moschata Duchesne) were investigated. Peroxidase activities of internode and leaf tissues of the bush plants were higher than those of respective vine tissues. Roots of bush plants, however, had a lower peroxidase activity than vine plants. In both bush and vine plants, peroxidase activities were lower in leaf tissues than in root and internode tissues. Electrophoretic comparisons revealed qualitative differences in peroxidase patterns in internodes between bush and vine plants. Moreover, qualitative differences between internode and root profiles were found between bush and vine plants in C. moschata. In conclusion, the results of this report revealed that a single gene conferring the bush phenotype in C. moschata might affect the relative expression of peroxidase activity, peroxidase isozymes, and protein profiles in leaf, internode, and root tissues.

Saline-Dependent Regulation of Manganese Peroxidase Genes in the Hypersaline-Tolerant White Rot Fungus Phlebia sp. Strain MG-60

The expression pattern of manganese peroxidases (MnPs) in nitrogen-limited cultures of the saline-tolerant fungus Phlebia sp. strain MG-60 is differentially regulated under hypersaline conditions at the mRNA level. When MG-60 was cultured in nitrogen-limited medium (LNM) containing 3% (wt/vol) sea salts (LN-SSM), higher activity of MnPs was observed than that observed in normal medium (LNM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated that two MnP isoenzymes were de novo synthesized in the culture of LN-SSM. Three MnP-encoding genes (MGmnp1, MGmnp2, and MGmnp3) were isolated by reverse transcription (RT)-PCR and rapid amplification of cDNA ends PCR techniques. The corresponding isozymes were identified by peptide mass fingerprinting analysis. MnP isozymes encoded by MGmnp2 and MGmnp3 were observed mainly in LN-SSM. Real-time RT-PCR analysis revealed high levels of MGmnp2 and MGmnp3 transcripts in LN-SSM 48 h after the addition of 2% NaCl. The induction of MnP production and the accumulation of gene transcripts by saline were well correlated in the presence of Mn(2+). However, in the absence of Mn(2+), there was no clear correlation between mnp transcripts levels and MnP activity, suggesting posttranscriptional regulation by Mn(2+).

Effect of age on sexually dimorphic selenoprotein expression in mice

Clinical data suggest that selenium (Se) supplementation decreases disease predisposition and severity and accelerates recovery in a variety of pathologies. Pre-supplementation Se levels and sex represent important determinants of these Se-dependent health effects. Accordingly, we previously reported on sexually dimorphic expression patterns of Se-dependent glutathione peroxidase 1, type I deiodinase, and selenoprotein P in young mice. In the present study we investigated whether these differences vary with age. The strong sexual dimorphic expression of hepatic type I deiodinase that was observed in young mice vanished both at the mRNA and enzyme activity level by 1 year of age. In contrast, the strong sex-specific differences in renal type I deiodinase mRNA expression were sustained with age. Accordingly, deiodinase enzymatic activities differed in male and female kidneys, largely independent of age [average of 6.8 vs. 15.7 pmol/(min mg) in males vs. females]. In parallel, hepatic Se concentrations and glutathione peroxidase activities increased in female mice compared to male littermates, establishing a new sexual dimorphism in liver. Thus, age represents another important modifier of the dynamic sex- and tissue-specific selenoprotein expression patterns. These data highlight again the unique physiological regulatory mechanisms that have evolved to control Se metabolism according to the actual needs of the organism.

Polar vineyard pruning extracts increase the activity of the main ligninolytic enzymes in Lentinula edodes cultures

Lentinula edodes is considered an alternative recycling agent for agricultural wastes, and there have been several studies to understand the relationship between its growth and ligninolytic activity. We tested the effect of wood from viticulture pruning, extracted with solvents of differing polarity, on the biomass production and activity pattern of ligninolytic enzymes. The analysis was done by measuring the mycelial dry mass and enzyme activity of liquid growth medium during the culture of L. edodes, adding either single extracts or a combination of extracts. Polar extracts enhanced mycelial production, and the activity patterns of lignin peroxidase, manganese peroxidase, aryl alcohol oxidase, and laccase were comparable to their activities predicted by ligninolysis models proposed for other fungi. We conclude that the polar extracts could be useful for enhancing fungal biomass production and for modifying lignin degradation because the regulation of ligninolytic enzyme activity is differentially influenced by the polarity of the extract.

Change in phenylalanine ammonia lyase activity and isozyme patterns of polyphenol oxidase and peroxidase by salicylic acid leading to enhance resistance in cowpea against Rhizoctonia solani

In this paper, we describe a study concerning the determination of phenylalanine ammonia lyase (PAL) activities leading to decline in disease progress caused by Rhizoctonia solani after application of salicylic acid (SA). Two applications of 1.4 mM SA (pH 6.5) followed by inoculation with Rhizoctonia solani resulted in a quantitative change in polyphenol oxidase (PPO), peroxidase (PRX) isoforms and increase in PAL activities from 4.38 to 19.48 unit g−1 (FM) h−1 in Bundel-1, UPC-4200 and IFC-902 cowpea genotypes. Increase in PAL activities was further observed specifically in UPC-4200 when plants were exposed with Rhizoctonia solani spores. Total soluble proteins did not change after SA treatment, however they were significantly increased in SA sprayed-inoculated UPC-4200 genotype. Of the ten detected isoforms of polyphenol oxidase, isoforms 7 and 10, and isoform 4 of peroxidase showed increased activities by SA application. The disease symptoms measured as areas under progress curve (AUDPC) indicated less A value in SA sprayed Bundel-1 and UPC-4200 genotypes over their controls.

DNA-fingerprinting (AFLP and RFLP) for genotypic identification in species of the Pleurotus eryngii complex

Wild populations of edible species are important source of genetic variability for cultivated lines that can undergo a drastic loss of diversity resulting from man's selection. The development of tools aimed at the clear-cut and safe identification and assessment of genetic variability of the wild and cultivated strains is thus a fundamental goal of molecular genetic research. In this study, we used two polymerase chain reaction (PCR)-based fingerprinting methods-amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) of laccase and manganese peroxidase genes-to assess genetic differences among strains and independently evolving lineages belonging to the Pleurotus eryngii complex. Both laccase RFLP and AFLP have been proved to distinguish unambiguously the three taxa studied: Pleurotus ferulae, P. eryngii, and P. eryngii var. nebrodensis. AFLP also showed enough sensitivity to detect polymorphisms among the strains, proving to be an efficient DNA fingerprinting tool in studies of strain assignment. The divergent RFLP laccase and manganese peroxidase patterns are also discussed in relation to the role played by these genes in the interaction between these fungi and their host plants.

Variability of antioxidant enzyme activity and isoenzyme profile in needles of Serbian spruce ( Picea omorika (Panč.) Purkinye)

Variations were studied of the activity and isoenzyme patterns of soluble peroxidase, catalase, catechol oxidase and superoxide dismutase, in needles of the Balkan endemic conifer Serbian spruce, Picea omorika (Panč.) Purkinye. The samples were collected from the natural habitat of the species, Mt. Tara. Seasonal changes were found to affect enzymatic activities and isoenzyme profiles. Total protein content was significantly lower in the summer than in other seasons. Several isoforms of peroxidase, catechol oxidase and superoxide dismutase (SOD), as well as two catalase isoenzymes were detected. The number of peroxidase isoenzymes was greatest during the vegetative season. Catalase and catechol oxidase peaked in summer and spring, respectively. Total SOD and Mn-SOD activities were significantly higher in the winter samples than the summer ones.

Antioxidative enzymes during germination of two lines of Serbian spruce [Picea omorika (Panc.) Purkyně

Two lines of Picea omorika (Panc.) Purkyn? were compared with respect to germination percentage as well as specific activity and isoenzyme pattern of catalase, superoxide dismutase, and peroxidase (POD) during germination. Line A had a higher germination percentage and higher enzyme activities in dry seeds and seedlings compared to line C. Peroxidase activity was not detected in dry seeds, but measured up to 10 U/g and 28 U/g on the 7th day of germination in lines C and A, respectively. The most abundant POD basic isoform in seedlings of both lines (pI 8.2) was not found previously in needles of adult Serbian spruce trees of the same lines. .

Cadmium induced changes in cell wall peroxidase isozyme pattern in barley root tips

Changes in peroxidase activity as well as isozyme peroxidase pattern were analyzed in five cell wall (CW) fractions of barley roots exposed to 1mM CdCl<sub>2</sub>for 48 and 72 h. Whereas strong inhibition of peroxidase activity was detected in fraction CW I and weak inhibition in fractions CW II, III and IV, strong activation of peroxidase was observed in fraction V after Cd application. Despite the inhibition of enzyme activity in most CW fractions, induction of several isoperoxidases was discovered after separation on PAGE. In fraction CW I inhibition of one cathodic isoperoxidase and activation of two anodic and two cathodic isoperoxidases was detected. Additional two anodic and one cathodic Cd-induced isozyme appeared in CW II and CW III. Strongly activated anodic isoperoxidase was detected in fraction CW V. Our results demonstrate that monitoring the stress modified peroxidase activity in enzyme extracts using guaiacol as a non-specific peroxidase substrate is not sufficient enough. Since some isozymes can be activated and some inhibited, isozyme pattern analysis is recommended.

Studies on the superoxide anion production and peroxidase activity in potato leaf cell suspension exposed to salicylic acid

It is now widely accepted that salicylic acid (SA) signaling is mediated by reactive oxygen species (ROS) production. We have studied the effect of SA on peroxidase activity and superoxide anion production in potato leaf cell suspension. The results show that potato cells are insensitive to low concentrations of exogenous SA (< 1 mM) and the effect is observed at 1–5 mM SA. The cells exposed to SA exhibit higher peroxidase activity and show different peroxidase pattern when analyzed on native gels compared to the control. Superoxide anion production is enhanced after two hours of treatment and 2.5 mM SA gives the highest value. The results suggest peroxidase-mediated detoxification of ROS elicited by SA.

Assessment of genetic purity of micropropagated plants of sugarcane by isozyme and RAPD analysis

Shoot tip expiants of nine sugarcane varieties(Saccharum species hybrid.), CoLk 8102, CoLk 8001, CoS 767, CoLk 9606, CoLk 9617, CoS 95255, BO 91, CoJ 64 and Co 1148, were established on a solid MS medium containing 0.8% agar, 3% sucrose and 0.05mg/l of IAA, BAP and kinetin. Shoot regeneration has been achieved in liquid MS medium containing 0.5mg/l each of IAA, BAP and kinetin. Multiple shoots were obtained on liquid MS medium containing 0.01mg/l IAA, 0.5mg/l each of 6- benzyl aminopurine (BAP), kinetin and rooting occurred in 1/2 strength liquid MS medium with 5.0 mg/l NAA and 0.01 mg/l each of BAP and kinetin. To detect the genetic purity of in vitro raised plantlets, expression of iso-peroxidases in donor plants andin vitro raised plantlets was compared through native PAGE. Different genotypes showed marked variation regarding number, position and intensity of bands. Micropropagated plantlets showed identical pattern of peroxidases to their parental clones. The genetic stability of micro propagated plantlets was also tested by RAPD analysis. The banding pattern of PCR amplified products from micro propagated plantlets was monomorphic based on RAPD profile in all the varieties. RAPD analysis and peroxidase isozyme pattern confirmed the genetic purity of sugarcane plantlets derivedin vitro.

Expression pattern of cytosolic glutathione peroxidase (cGPx) mRNA during mouse embryogenesis

The selenoprotein cytosolic glutathione peroxidase (cGPx) is ubiquitously distributed in a variety of organs, and its primary function is to protect oxidative damage. To investigate the spatial and temporal expression pattern of cGPx mRNA in embryogenesis, as this has not been studied before, reverse transcription-polymerase chain reaction (RT-PCR) was carried out in a thermal cycler using mouse-specific cGPx primers, and in situ hybridization was performed in whole embryos or embryonic tissues using digoxigenin-labeled mouse cGPx riboprobes. Expression of cGPx mRNA was detected in all the embryos retrieved from embryonic days (EDs) 7.5 to 18.5. On EDs 10.5-12.5, cGPx mRNA was highly expressed in the margin of forelimb and hindlimb buds and dorsally in the cranial neural tube, including the telencephalon, diencephalon, and hindbrain neural tube. On ED 13.5, cGPx mRNA was accumulated especially in vibrissae, forelimb and hindlimb plates, tail, and spinal cord. On EDs 14.5-16.5, cGPx mRNA was found in the developing brain, Rathke's pouch, thymus, lung, and liver. On ED 17.5, the expression of cGPx mRNA was apparent in various tissues such as brain, submandibular gland, vibrissae, heart, lung, liver, stomach, intestine, pancreas, skin, and kidney. In particular, cGPx mRNA was greatly expressed in epithelial linings and metabolically active sites such as whisker follicles, alveolar epithelium of lung, surface epithelium and glandular region of stomach, skin epithelium, and cortex and tubules of kidney. Overall results indicate that cGPx mRNA is expressed in developing embryos, cell-specifically and tissue-specifically, suggesting that cGPx may function to protect the embryo against reactive oxygen species and/or hydroperoxides massively produced by the intracellular or extracellular environment.

Biochemical changes in barley plants after excessive supply of copper and manganese

The present study was undertaken to identify changes in some important proteins involved in CO 2 fixation (Rubisco, Rubisco activase (RA), Rubisco binding protein (RBP)), NH 4 + assimilation (glutamine synthetase (GS) and glutamate synthase (GOGAT)), using immunoblotting, and in the antioxidative defense as a result of Cu or Mn excess in barley leaves ( Hordeum vulgare L. cv. Obzor). Activities and isoenzyme patterns of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT), as well as the levels of ascorbate (ASC), non-protein sulfhydryl groups, hydrogen peroxide and oxidative damage to proteins were determined. Data were correlated to the accumulation of Cu or Mn in the leaves after 5 days supply of heavy metal (HM) excess in the nutrient solution. In the highest Cu excess (1500 μM), Rubisco LS and SS were reduced considerably whereas under the highest Mn concentrations (18,300 μM) only minor changes in Rubisco subunits were detected. The RBP was diminished under the highest concentrations of both Cu or Mn. The bands of RA changed differently comparing Cu and Mn toxicity. GS decreased and GOGAT was absent under the highest concentration of Cu. At Mn excess Fd-GOGAT diminished whereas GS was not apparently changed. The development of toxicity symptoms corresponded to an accumulation of Cu or Mn in the leaves and to a gradual increase in protein carbonylation, a lower SOD activity and elevated CAT and GPX activities. APX activity was diminished under Mn toxicity and was not changed under Cu excess. Generally, changes in the isoenzyme profiles were similar under both toxicities. An accumulation of H 2O 2 was observed only at Mn excess. Contrasting changes in the low-molecular antioxidants were detected when comparing both toxicities. Cu excess affected mainly the non-protein SH groups, while Mn influenced the ASC content. Oxidative stress under Cu or Mn toxicity was most probably the consequence of depletion in low-molecular antioxidants as a result of their involvement in detoxification processes and disbalance in antioxidative enzymes. The link between heavy metal accumulation in leaves, leading to different display of oxidative stress, and changes in individual chloroplast proteins is discussed in the article.

Seasonal pattern of antioxidant enzyme system in the roots of perennial forage grasses grown in alpine habitat, related to freezing tolerance

The relationship between active oxygen species (AOS) and membrane damage, and between antioxidant enzyme activity and chilling tolerance has been documented, but the mechanisms responsible for perennial forage grass to survive winter with temperatures at −30°C in temperate alpine regions is not well understood. In this study, the seasonal pattern of enzymatic antioxidant systems superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11) and lipid peroxidation in roots and leaves of alpine perennial grasses grown in their natural environment were investigated to understand the role of the enzymatic antioxidant system in freezing tolerance of perennial grasses. Four grasses, Poa sphyondylodes Trine., Bromus inermis Leyss., Bromus sinensis Keng. and Elymus nutans Griseb., were established in alpine conditions in 1993. The grasses were sampled at approximately semi‐monthly intervals in the autumn of 1995 and spring of 1996. The results showed that leaves were dead in the autumn and membrane damage seems to play a key role in the decline of this organ. Antioxidant enzyme activities of the roots strongly changed with declining temperature in the autumn and winter or increasing temperature in the spring. With the decrease in temperature in the autumn the antioxidant enzyme activities increased rapidly, reaching maximum values in early November and then slowly declining during the following winter period, although they were still higher than in September In the spring, antioxidant enzymes activities increased again in the roots with the rise of temperature from mid April to early May when the shoots began re‐growth. In contrast, thiobarbituric acid‐reactive substances content in the roots increased markedly in the autumn, reaching maximum values in early October and remaining constant with little fluctuation during the following winter. In the autumn when the roots experienced winter acclimation, the formation of freezing tolerance in the roots was correlated with the activities of the antioxidant enzyme, indicating that antioxidant activity systems in the roots played an important role in limiting the production of free radicals to protect membrane integrity. Freezing tolerance in alpine grasses correlated with an increased capacity to scavenge or detoxify activated AOS by the antioxidant enzymatic system. AOS accumulated with decreasing temperature in early cold acclimation may be an inducer in activating the antioxidant enzyme defence system for the formation of freezing tolerance in roots.

Nutrient status and enzyme activity alteration in cucumber seedlings as a response to boron deficiency

Cucumber (Cucumus sativus L. var. Beit alpha) seedlings were grown in two groups on boron-deficient (traces of boron) and boron-sufficient (10.0 µM boron) hydroponic media for 30 days under controlled conditions. At harvest, the concentrations of magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were determined in addition to boron (B) in the dry tissues of roots and leaves. The concentration of phenolic compounds in the roots was also determined. Peroxidase (POD) and catalase (CAT) enzyme activity was assayed in the fresh plant material. In addition, changes in the peroxidase and catalase isozyme patterns were also identified. The results showed that the vegetative growth of cucumber plants was negatively affected by boron deficiency. Biomass accumulation decreased by as much as 24.3% in the shoots and 49.1% in the roots. The nutrient concentrations in both the leaves and roots of B-stressed plants were substantially lower. Phenolic compounds were accumulated in significant amounts in the roots of deficient plants. The peroxidase and catalase enzyme activities were significantly increased in the tissues of deficient plants and new isozymes were induced or activated. The irregular biochemical changes occurring in B-deficient plants were explained as a plant physiological response to B-deficient conditions.

Antioxidant Enzyme Isoforms on Gels in Two Poplar Clones Differing in Sensitivity After Exposure to Ozone

The effect of acute ozone (O3) fumigation on isozyme patterns of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) in mature (ML) and young leaves (YL) of two poplar clones, contrasting in O3-sensitivity was analysed. Untreated leaves of both the O3-sensitive (O3-S) clone Eridano of Populus deltoides×P. maximowiczii and the O3-resistant (O3-R) clone I-214 of P.×euramericana showed four distinct SOD isoforms with a relative mobility (Rf) of 0.54 (MnSOD), 0.60 (Cu/ZnSOD), 0.65 (unidentified), and 0.71 (Cu/ZnSOD). After O3-fumigation the activity of the SOD isoforms showed only quantitative variations with respect to control plants. In ML of untreated O3-R plants seven POD isoforms (Rf= 0.13, 0.19, 0.34, 0.59, 0.64, 0.70 and 0.75) were found, while in YL one isoform (Rf= 0.34) was undetected. Only three POD isoforms in both ML and YL of untreated O3-S plants were resolved. The electrophoretic pattern of POD in O3-S leaves was greatly modified by acute O3-fumigation with the appearance of new isoforms in both YL and ML and the disappearance of an isoform (Rf= 0.13) in YL. Additionally, O3-exposure induced the appearance of two APX isoforms in YL (Rf= 0.66 and 0.70), and one isoform in ML (Rf= 0.70) of the O3-S clone. By contrast, the activity of the three APX isoformes (Rf= 0.64, 0.70 and 0.76) detected in O3-R leaves showed only quantitative variation with respect to untreated plants. From these data it is concluded that: 1) in these poplar hybrids antioxidant enzyme activity is developmentally regulated and greatly affected by acute O3 stress treatments and 2) the different enzymes activity displayed by the two poplar clones, especially for POD and APX isoformes, could partly explain their distinct O3-sensitivity.

Activity and isoforms of peroxidases, lignin and anatomy, during adventitious rooting in cuttings of Ebenus cretica L.

Adventitious rooting of Ebenus cretica cuttings was studied in order to examine a) the rooting ability of different genotypes in relation to electrophoretic patterns of peroxidases. b) the activity and electrophoretic patterns of soluble and wall ionically bound peroxidases, the lignin content and anatomical changes in the control and IBA treated cuttings of <rooting> and <non-rooting> genotypes in the course of adventitious root formation. In addition, a fraction of soluble cationic peroxidases was separated by gel filtration chromatography from the total soluble peroxidases of a <rooting> genotype. No rooting occurred in cuttings without IBA-treatment. In both genotypes, electrophoretic patterns of soluble anionic peroxidases revealed two common peroxidase isoforms, while a fast-migrating anionic peroxidase isoform (A3) appeared only in <rooting> genotypes. Both genotypes showed similar patterns of soluble, as well as wall ionically bound cationic peroxidase isoforms. The number of isoforms was unchanged during the rooting process (induction, initiation and expression phase) but an increase in peroxidase activity (initiation phase) followed by decrease has been found in IBA-treated cuttings. During initiation phase the lignin content was almost similar to that on day 0 in <rooting> genotype while it was reduced at by about 50% in <non-rooting> genotype at the respective time. Microscopic observations revealed anatomical differences between genotypes. According to this study, the <rooting> and <non-rooting> genotypes display differences in anatomy, lignin content, activity of soluble peroxidases and the electrophoretic patterns of soluble anionic peroxidase isoforms. The A3-anionic peroxidase isoform could be used as biochemical marker to distinguish <rooting> and <non-rooting> genotypes of E. cretica and seems to be correlated to lignin synthesis in rooting process.

A Quantitative and Qualitative Analysis of Antioxidant Enzymes in Relation to Susceptibility of Apples to Superficial Scald

The activities and isoenzyme patterns of guaiacol-dependent peroxidase (POX), ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT) were studied in yellow- and red-fruited crab apple [Malus (L.) Mill.] selections from a `White Angel' × `Rome Beauty' cross that show differential susceptibility to the physiological storage disorder, superficial scald. There were no consistent relationships between total enzyme activities and scald incidence, high activities of the enzymes being detected in selections with both high and low susceptibilities to scald. However, additional individual isoforms of some antioxidant enzymes were detected in the scald-resistant selections when compared with scald-susceptible selections. In a native gel system, four guaiacol-dependent POX isoenzymes were detected in both yellow and red scald-resistant selections compared with only two in scald-susceptible selections. Similarly, for anodic acidic POX assayed using benzidine, six isoenzymes were detected in both yellow and red scald-resistant selections compared with five in yellow and four in red susceptible selections. Ten SOD isozymes were detected in scald-resistant yellow-fruited selections compared with only five faint bands in scald-susceptible selections, but similar patterns were not detectable for red-fruited selections. Differences in the presence of various isoenzymes for CAT and APX were also detected among the selections, but associations with scald susceptibility were also affected by fruit color or were inconsistent. The presence or absence of individual isoenzymes may be a better indication of scald resistance or susceptibility than the total enzyme activities. Isoenzyme analyses, especially of POX, could be useful to breeders for the early detection of scald resistance/susceptibility in apples.