Effect of hydroxytyrosol‐rich preparations on phenolic‐linked antioxidant activity of seeds

Hydroxytyrosol‐rich extract (HRE) and hydroxytyrosol‐rich olive mill wastewater (HROMW) were used as exogenous growth enhancers to stimulate tomato seedling vigor. The tomato seeds soaking in 10% w/v HROMW or HRE solutions were optimum in maximally enhancing seedling performance according to biochemical seed vigor parameters. Biochemical parameters as the average glucose‐6‐phosphate dehydrogenase (G6PDH) activity in HRE‐treated seeds (915.11 nmoles min^?1 mg^?1 protein) was higher than control (629.58 nmoles min^?1 mg^?1 protein) and correlated with the increased phenolic content (3530 μg g^?1 fw) and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH)‐based antioxidant activity (70.60%), respectively. Some key enzymes, guaiacol peroxidase (GPX) (6100.65 nmoles min^?1 mg^?1 protein) and catalase (2.04 μmoles min^?1 mg^?1 protein), were also higher in response to treatments and correlated with enhanced phenolic content and antioxidant activity. This study supports the hypothesis that the exogenous phenolic application stimulates the pentose phosphate pathway through an over‐expression of endogenous phenolic synthesis and an increase in free‐radical scavenging antioxidant activity. Therefore, the current study indicates the enhancement of seed vigor by HRE especially and HROMW as reflected by the stimulation of biochemical responses.     

Stimulation of total phenolics, L-DOPA and antioxidant activity through proline-linked pentose phosphate pathway in response to proline and its analogue in germinating fava beans (Vicia faba)

The rationale behind the study was to enhance azetedine-2-carboxylate (A2C)-linked stress in the germinating seeds to which it responds by increased proline synthesis to overcome inhibition of proline dehydrogenase (PDH). A2C is a competitive inhibitor of proline that inhibits its transport from cytosol to the mitochondria for further metabolic recycling by binding on to the active sites of PDH. The enhanced synthesis of proline would increase the ratio of the cofactors NADP/NADPH₂. The increase in the cofactors would result in the over-expression of the phenypropanoid pathway required for the phenolic acids and L-DOPA synthesis via pentose phosphate pathway through the activity of glucose-6-phosphate dehydrogenase (G6PDH). Fava bean were chosen since it has high phenolic and L-DOPA levels and could be an important part of the diet especially for patients suffering from Parkinson's Disease. The objectives were investigated by assaying for total phenolic content, the corresponding antioxidant activity by β-carotene oxidation method, proline levels and enzymes such as G6PDH and guaiacol peroxidase (GPX) using spectrophotometric methods. L-DOPA was quantified using HPLC. The fava bean seeds were primed with water, 200 μM A2C, 0.25 mM proline and a combination of A2C and proline treatments. After the priming stage, seeds were dark germinated and grown for a period of 8 days, for biochemical analysis. L-DOPA levels did not change in comparison to the control treatments while total phenolic content, proline and G6PDH were all enhanced by the treatments. During the early stages of germination the phenolic acids were antioxidant in nature, which later was reduced as they become polymerized to lignins and lignans via the GPX activity. Total phenolic synthesis was both coupled and uncoupled to PLPPP depending on the treatments. The three treatments over-expressed PLPPP since large difference between control and the treatments were observed for all parameters, except L-DOPA content.     

Clonal response to cold tolerance in creeping bentgrass and role of proline-associated pentose phosphate pathway

Single seed origin creeping bentgrass (‘Penncross’) clonal lines were screened to find genetic heterogeneity, which reflected diversity of phenolic production linked to cold stress within a cross-pollinated cultivar. In this study, total soluble phenolic and antioxidant activity varied among 20 creeping bentgrass clonal lines, confirming wide heterogeneity in this cross-pollinated species. Correlations between phenolic content and proline-associated pentose phosphate pathway were also found among the clonal lines. The active metabolic role of proline in cellular metabolic adjustment to cold stress and its support for likely energy synthesis via mitochondrial oxidative phosphorylation was inferred in creeping bentgrass clonal lines based on the activity of proline dehydrogenase. Results of photochemical efficiency of these clonal lines after cold temperature treatment (4 °C) also indicated a close association between stress tolerance and proline-associated pentose phosphate pathway regulation for phenolic biosynthesis and antioxidant response. This study provides a sound metabolic based rationale to screen bentgrass clonal lines for enhanced cold stress tolerance.     

Enhancement of seed vigour following insecticide and phenolic elicitor treatment

Thiamethoxam (CGA 293'343) is a novel broad-spectrum neonicotinoid insecticide. It is commercially used as a seed treatment under the trademark Cruiser (CRZ). Although many reports detail its insecticidal, plant-protecting properties, there are minimal reports concerning the effect on seed germination activities which can be key control points of seedling vigour. In this report, we investigated the effect of CRZ, fish protein hydrolysates (FPH; a known elicitor of pentose-phosphate pathway) and the combination of CRZ and FPH (CF) on seed vigour of pea, soybean and corn. Seed vigour was investigated by estimating germination percentage, shoot height, shoot weight, total soluble phenolic content, antioxidant content, G6PDH (glucose-6-phosphate dehydrogenase) activity, and GPX (guaiacol peroxidase) activity. Addition of FPH to CRZ (CF) seemed to have a slightly positive effect on seed vigour, especially, CF and FPH treatment for corn and FPH treatment for pea, suggesting that pre-sowing treatments may cause positive/negative effects on seed vigour, depending on the concentration of treatments. Further research will be needed to determine their effects and the optimal concentration for seed priming.     

Stimulation of the pentose phosphate pathway and glutathione levels by dehydroascorbate, the oxidized form of vitamin C.

Ascorbic acid, or vitamin C, generally functions as an antioxidant by directly reacting with reactive oxygen intermediates and has a vital role in defenses against oxidative stress. However, ascorbic acid also has pro-oxidant properties and may cause apoptosis of lymphoid and myeloid cells. The present study shows that dehydroascorbate, the oxidized form of vitamin C, stimulates the antioxidant defenses of cells, preferentially importing dehydroascorbate over ascorbate. While 200-800 microM vitamin C caused apoptosis of Jurkat and H9 human T lymphocytes, pretreatment with 200-1000 microM dehydroascorbate stimulated activity of pentose phosphate pathway enzymes glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and transaldolase, elevated intracellular glutathione levels, and inhibited H(2)O(2)-induced changes in mitochondrial transmembrane potential and cell death. A 3. 3-fold maximal glutathione elevation was observed after 48 h stimulation with 800 microM dehydroascorbate. In itself, dehydroascorbate did not affect cytosolic or mitochondrial reactive oxygen intermediate levels as monitored by flow cytometry using oxidation-sensitive fluorescent probes. The data reveal a novel mechanism for increasing glutathione levels through stimulation of the pentose phosphate pathway and identify dehydroascorbate as an antioxidant for cells susceptible to the pro-oxidant and proapoptotic properties of vitamin C.     

Seed vigour studies in corn, soybean and tomato in response to fish protein hydrolysates and consequences on phenolic-linked responses

Seed priming with fish protein hydrolysates (FPH) has been studied for the enhancement of seed vigour of corn, soybean and tomato. The influence of FPH at 2.5 mL/L and 5.0 mL/L on traditional agronomic parameters for seed vigour (germination percentage, seedling weight, seedling height) and potential new vigour-associated parameters (phenolic content, antioxidant activity, guaiacol peroxidase (GuPX) activity, chlorophyll content) was investigated. FPH treatment preferentially stimulated seedling vigour in the following order: soybean>tomato>corn. For soybean, FPH at 2.5 mL/L and 5 mL/L improved the majority of the seed vigour parameters (seedling weight and height, phenolic content, antioxidant activity and chlorophyll content, and lignification-associated GuPX activity). Similarly, for tomato, FPH at 2.5 mL/L stimulated seedling weight and height, GuPX activity and chlorophyll content. However, FPH did not stimulate corn seed vigour. Our results suggest an ability of proline precursor-rich FPH to improve of plant growth and development (e.g., seed vigour) in phenolic-rich plant species through modulation of phenolic and chlorophyll metabolisms.     

The role of proline-associated pentose phosphate pathway in cool-season turfgrasses after UV-B exposure

Physiological adjustments of cool-season turfgrasses were investigated to determine the role of proline-associated pentose phosphate pathway for phenolic biosynthesis and stimulation of antioxidant response system following UV-B exposure. Creeping bentgrass, Kentucky bluegrass, tall fescue, and perennial ryegrass plugs were subjected to artificial UV-B exposure (biologically effective UVB_BE radiation 8 kJ m⁻² d⁻¹.) for one week with 10-h photoperiod. Significant accumulation of phenolics and stimulation of antioxidant enzyme activity was observed in all investigated cool-season turfgrasses after UV-B exposure and this induction corroborated with higher glucose-6-phosphate dehydrogenase activity and high accumulation of proline. Guaiacol peroxidase activity also increased in all investigated cool-season turfgrass species after UV-B exposure. In this study, the shift of carbon flux from glycolysis to pentose phosphate pathway following UV-B exposure and as a result of that, the higher accumulation of phenolics and stimulation of antioxidant response system provides an insight to understand a probable defense mechanism of cool-season turfgrasses against UV stress.     

Pentose phosphate metabolism during dormancy breakage in Corylus avellana L.

Commercially obtained fruits of Corylus avellana exhibit the characteristic loss of dormancy of this seed following chilling under moist conditions. The activities of cytosolic and organellar enzymes of pentose phosphate pathway in cotyledonary tissue were assayed throughout stratification and over a similar period in damp vermiculite at 20° C. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconic acid dehydrogenase (6PGDH) were both found in cytosolic extracts in all treatments; only 6PGDH was present in the organellar fraction.The enzyme activities monitored in seeds at 20° C remained relatively constant over the course of the investigation except in the case of cytosolic 6PGDH where it is suggested an inhibitor of the enzyme accumulated. This inhibitor was removed by the partial purification procedure. Increases in the activities of the enzymes occurred during stratification, the major increase coinciding exactly with dormancy breakage but prior to the initiation of germination. The marked increase in G6PDH and 6PGDH concurrent with the change in germination potential of the chilled seed may have considerable biochemical significance in breaking down the dormant state.Abbreviations G6P glucose-6-phosphate - G6PDH glucose-6 phosphate dehydrogenase - NADP nicotinamide adenine dinucleotide phosphate - 6 PGDH 6-phosphogluconic acid dehydrogenase - PPP pentose phosphate pathway     

The effect of phenols on respiratory enzymes in seed germination

Low molecular weight phenolic compounds were identified in two soilswith different vegetative cover, Fagus sylvatica, L. andPinus laricio, Poiret, spp. calabrica, and were tested atdifferent concentrations on seed germination of Pinuslaricio, and on respiratory and oxidative pentose phosphate pathwayenzymes involved in the first steps of seed germination. The data obtained showthat there are marked differences in the phenolic acid composition of the twoinvestigated soils. All the phenolic compounds bioassayed inhibited seedgermination and those extracted from Pinus laricio soilwere particularly inhibitory. We also found that the non-germination of seedsisstrongly correlated to the inhibition of the activities of enzymes ofglycolysisand the oxidative pentose phosphate pathway.     

Functional significance of the pentose phosphate pathway and glutathione reductase in the antioxidant defenses of human sperm

Glutathione peroxidase is one of the principal antioxidant defense enzymes in human spermatozoa, but it requires oxidized glutathione to be reduced by glutathione reductase using NADPH generated in the pentose phosphate pathway. We investigated whether flux through the pentose phosphate pathway would increase in response to oxidative stress and whether glutathione reductase was required to protect sperm from oxidative damage. Isotopic measurements of the pentose phosphate pathway and glycolytic flux, thiobarbituric acid assay of malondialdehyde for lipid peroxidation, and computer-assisted sperm analysis for sperm motility were assessed in a group of normal, healthy semen donors. Applying moderate oxidative stress to human spermatozoa by adding cumene hydroperoxide, H(2)O(2), or xanthine plus xanthine oxidase or by promoting lipid peroxidation with ascorbate increased flux through the pentose phosphate pathway without changing the glycolytic rate. However, adding higher concentrations of oxidants inhibited both the pentose phosphate pathway and glycolytic flux. At concentrations of 50 microg/ml or greater, the glutathione reductase-inhibitor 1,3-bis-(2-chloroethyl) 1-nitrosourea decreased flux through the pentose phosphate pathway and blocked the response to cumene hydroperoxide. It also increased lipid peroxidation and impaired the survival of motility in sperm incubated under 95% O(2). These data show that the pentose phosphate pathway in human spermatozoa can respond dynamically to oxidative stress and that inhibiting glutathione reductase impairs the ability of sperm to resist lipid peroxidation. We conclude that the glutathione peroxidase-glutathione reductase-pentose phosphate pathway system is functional and provides an effective antioxidant defense in normal human spermatozoa.     

Relationship of secondary metabolism to growth in oregano (Origanum vulgare L.) shoot cultures under nutritional stress

Micropropagation of Origanum vulgare L. by shoot buds, as a potential model system for studying carbon skeleton diversion from growth to secondary metabolism as adaptive response to nutrient deficiency, has been performed. In addition, the antioxidant phenolic compounds, produced by shoots under nutritional stress or in response to exogenously added proline, have been studied. Caffeic acid, rosmarinic acid, and lithospermic acid B have been isolated in oregano shoot cultures by reversed-phase high-performance liquid chromatography, and their structures have been elucidated by tandem mass spectrometry. Both nutritional stress, which in turn causes a moderate increase of constitutive free proline, and exogenous proline affect growth and antioxidant phenolic content of oregano shoots, compared to control.The role of proline, and the associated redox cycle, as a form of metabolic signaling based on a transfer of redox potential amongst interacting cell pathways, which in turn elicit phenolic metabolism via stimulated carbon flux through oxidative pentose phosphate pathway, is discussed. Furthermore, the potential use of oregano tissue and callus cultures as a new strategy to enable the production of useful secondary metabolites on a commercial scale is also discussed.     

Flavonoids influence growth and saccharide metabolism ofRhizobium meliloti

Supplementation of the growth media with flavonoids,viz. naringenin, flavone, quercetin and syringaldehyde, a phenolic compound and alfalfa seed exudate, differently affected the growth and saccharide metabolism ofRhizobium meliloti. Quercetin increased while syringaldehyde, flavone and alfalfa exudate decreased the growth and protein content ofR. meliloti cells. Naringenin had no effect on growth and protein content though it increased the exopolysaccharide production. Application of naringenin increased the activities of enzymes of the citrate cycle and the 6-phosphogluconate pathway, the major pathways of sugar metabolism in fast growing rhizobia, and decreased activities of glycolytic enzymes. The activities of enzymes of the pentose phosphate pathway remained unaffected by various treatments.     

Phytochemical and Antiproliferative Activity of Proso Millet

The phytochemical content, antioxidant activity and antiproliferative properties of three diverse varieties of proso millet are reported. The free phenolic content ranged from 27.48 (Gumi 20) to 151.14 (Mi2504-6) mg gallic acid equiv/100 g DW. The bound phenolic content ranged from 55.95 (Gumi20) to 305.81 (Mi2504-6) mg gallic acid equiv/100 g DW. The percentage contribution of bound phenolic to the total phenolic content of genotype samples analyzed ranged between 62.08% and 67.05%. Ferulic acid and chlorogenic acid are the predominant phenolic acid found in bound fraction. Caffeic acid and p-coumaric acid were also detected. Syringic acid was detected only in the free fraction. The antioxidant activity was assessed using the hydrophilic peroxyl radical scavenging capacity (PSC) assay. The PSC antioxidant activity of the free fraction ranged from 57.68 (Mi2504-6) to 147.32 (Gumi20) µmol of vitamin C equiv/100 g DW. The PSC antioxidant activity of the bound fraction ranged from 95.38 (Mizao 52) to 136.48 (Gumi 20) µmol of vitamin C equiv/100 g DW. The cellular antioxidant activity (CAA) of the extract was assessed using the HepG2 model. CAA value ranged from 2.51 to 6.10 µmol equiv quercetin/100 g DW. Antiproliferative activities were also studied in vitro against MDA human breast cancer and HepG2 human liver cancer cells. Results exhibited a differential and possible selective antiproliferative property of the proso millet. These results may be used to direct the consumption of proso millet with improved health properties.     

Synergistic effect of folic acid and vitamin B12 in ameliorating arsenic-induced oxidative damage in pancreatic tissue of rat

The efficacies of two nutritional factors, folic acid and vitamin B12, were assessed in this study against arsenic-induced islet cellular toxicity. Rats were divided into four groups consisting of five rats in each group: Group A, control; Group B, arsenic-treated; Group C, arsenic+folic acid; and Group D, arsenic+folic acid+vitamin B12. The dose of arsenic, folic acid and vitamin B12, respectively, was 3 mg, 36 microg and 0.63 microg kg(-1) body weight day(-1) for 30 days. Results showed that, compared to control group, there was a significant increase in the levels of nitric oxide (NO), malondialdehyde (MDA) and hydroxyl radical (OH-) formation in the pancreatic tissue of arsenic-treated rats, while the activity of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), and cellular content of antioxidant glutathione (GSH) were low in these animals. The serum level of tumor necrosis factor-alpha (TNF-alpha) and IL-6 was significantly high in these animals. Light microscopic examination showed a marked fall in the number of islet cells. Concomitant administration of either folic acid or folic acid and vitamin B12 with arsenic significantly restored all these parameters. Although folic acid alone could not restore the normal level of TNF-alpha and IL-6, combined folic acid and vitamin B12 could restore it. Folic acid and vitamin B12 combined also could recover islet cell count. These results suggest that folic acid+vitamin B12 are capable of reducing arsenic-induced cellular oxidative and inflammatory toxic changes. Thus, supplement with vitamin B12+folic acid may be predicted as a possible nutritional management strategy against arsenic-induced toxicity.     

The pentose phosphate pathway: an antioxidant defense and a crossroad in tumor cell fate

The pentose phosphate pathway, one of the main antioxidant cellular defense systems, has been related for a long time almost exclusively to its role as a provider of reducing power and ribose phosphate to the cell. In addition to this "traditional" correlation, in the past years multiple roles have emerged for this metabolic cascade, involving the cell cycle, apoptosis, differentiation, motility, angiogenesis, and the response to anti-tumor therapy. These findings make the pentose phosphate pathway a very interesting target in tumor cells. This review summarizes the latest discoveries relating the activity of the pentose phosphate pathway to various aspects of tumor metabolism, such as cell proliferation and death, tissue invasion, angiogenesis, and resistance to therapy, and discusses the possibility that drugs modulating the pathway could be used as potential tools in tumor therapy.     

UV-B induced changes in antioxidant enzymes and their isoforms in cucumber (Cucumis sativus L.) cotyledons

To assess the role of antioxidant defense system on exposure to ultra-violet-B (UV-B) radiation, the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of antioxidants ascorbic acid (AA) and alpha-tocopherol were monitored in cucumber (Cucumis sativus L. var long green) cotyledons. UV-B enhanced the activity of antioxidant enzymes as well as AA content, but decreased the level of alpha-tocopherol. Significant increase was observed in the activities of SOD and GPX. Analysis of isoforms of antioxidant enzymes by native-PAGE and activity staining revealed three isoforms of GPX in unexposed dark-grown cotyledons (control), and their intensity was enhanced by UV-B exposure. In addition, four new isoforms of GPX were observed in cotyledons after UV-B exposure. Although no new isoforms were observed for the other antioxidant enzymes, the activities of their existing isoforms were enhanced by UV-B.     

Coordination of Chloroplastic Metabolism in N-Limited Chlamydomonas reinhardtii by Redox Modulation (II. Redox Modulation Activates the Oxidative Pentose Phosphate Pathway during Photosynthetic Nitrate Assimilation)

The onset of photosynthetic NO3- assimilation in N-limited Chlamydomonas reinhardtii increased the initial extractable activity of the glucose-6-phosphate dehydrogenase (G6PDH), the key regulatory step of the oxidative pentose phosphate pathway. The total activated enzyme activity did not change upon NO3- resupply. The higher activity, therefore, represents activation of existing enzyme. No activation occurred during NH4+ assimilation. Incubation of extracts with DTT reversed the NO3- stimulation of G6PDH activity, indicating that the activation involved redox modulation of G6PDH. Phosphoribulosekinase, an enzyme activated by thioredoxin reduction, was inhibited at the onset of NO3- assimilation. A 2-fold stimulation of O2 evolution and a 70% decrease in the rate of photosynthetic CO2 assimilation accompanied the enzyme activity changes. There was an immediate drop in the NADPH and an increase in NADP upon addition of NO3-, whereas NH4+ caused only minor fluctuations in these pools. The response of C. reinhardtii to NO3- indicates that the oxidative pentose phosphate pathway was activated to oxidize carbon upon the onset of NO3- assimilation, whereas reduction of carbon via the reductive pentose phosphate pathway was inhibited. This demonstrates a possible role for the Fd-thioredoxin system in coordinating enzyme activity in response to the metabolic demands for reducing power and carbon during NO3- assimilation.     

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)     

Alternative Pathways of Glucose Utilization in Brain: Changes in the Pattern of Glucose Utilization and of the Response of the Pentose Phosphate Pathway to 5-Hydroxytryptamine During Aging

Abstract: The oxidation of differentially labelled glucose, pyruvate and glutamate in brain slices from rats aged 20 days to 26 months has been studied and the partition of the glucose used into the glycolytic-tricarboxylic acid cycle pathway, the pentose phosphate pathway and the glutamate-GABA shunt has been calculated. Over the time range 4 to 26 months, there is an approximately 20% decrease in the production of CO₂ via the glycolytic-tricarboxylic acid cycle route, as there is in the rate of glucose phosphorylation. The glutamate-GABA pathway falls by about 50% over this same time span. The broad activity of the pentose phosphate pathway falls rapidly and cannot be detected in the brains of rats aged 18 months or more, whereas the fully stimulated pathway, i.e. in the presence of the artificial electron acceptor phen-azine methosulphate, declines only marginally over this period, falling sharply only after 23 months. The pentose phosphate pathway is stimulated by the presence of 5-hy-droxytryptamine and this stimulation appears to increase with age.     

Activity of the pentose phosphate pathway during lignification

Summary We did this work to see if there is a correlation between lignin synthesis and the activity of the pentose phosphate pathway. Excision of the third internode of the stem of Coleus blumei Benth. followed by incubation on sucrose and indoleacetic acid led to extensive formation of tracheids. During this lignification we determined the activities of glucose-6-phosphate dehydrogenase and fructose-1,6-diphosphate aldolase, and the extent to which [1-¹⁴C]-,[3,4-¹⁴C]-, and [6-¹⁴C]glucose labelled CO₂ and the major cellular components. The results indicate that the pentose phosphate pathway was active during lignification, and that the activity of this pathway relative to glycolysis increased at the onset of lignification. Explants of storage tissue of Helianthus tuberosus L. were cultured under conditions which caused extensive lignification. ¹⁴CO₂ production from [1-¹⁴C]-, [3,4-¹⁴C]-, and [6-¹⁴C]glucose indicated activity of the pentose phosphate pathway during tracheid formation. We suggest that lignification is accompanied by appreciable activity of the pentose phosphate pathway and that this could provide the reducing power for lignin synthesis.Abbreviations NADP nicotinamide-adenine dinucleotide phosphate - IAA indoleacetic acid