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Hisashi Kato-Noguchi

Glycolysis has been shown to accelerate in many plant species, and the glycolytic pathway was considered to replace the Krebs cycle as the main source of energy when O2 becomes limiting. The increase in glycolytic flux is accompanied by the accumulation of glycolytic end products, including ethanol and lactate. Lactate dehydrogenase (LDH) has been isolated from several plant sources; however, there is very little work reported on LDH induction during anaerobiosis and no information is available on the long-term effect of low O2 atmosphere on lactic fermentation in carrot (Daucus carota L.) roots. To understand the regulation of metabolism of lactic fermentation, carrot root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2), or air at 5°C and 15°C. The concentration of lactate and the activity of LDH increased rapidly, reached peaks after 2 days, and then gradually decreased. The maximum increase level of LDH was 2.8-, 2.1-, 2.0-, and 1.6-fold; that of lactate was 5.6-, 3.8-, 2.9-, and 2.6-fold for 0.5% O2 at 15°C and 5°C, and 2% O2 AT 15°C and 5°C, respectively, compared with corresponding air control. These results indicate that the lactic fermentation was more accelerated in 0.5% O2 than 2% O2 atmosphere, and more accelerated at the higher storage temperature than the lower one. However, ethanol accumulation, which was found in the carrots under the same low-O2 atmosphere, was much more than lactate accumulation. Thus, carrot roots possess LDH, which appears under low-O2 atmosphere, but lactic fermentation may be a minor carbon flux compared to ethanolic fermentation.

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Hisashi Kato-Noguchi

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or air at 5 °C to investigate the effect of low O2 atmosphere on respiratory metabolism, particularly on lactate dehydrogenase (LDH) activity and its isozyme composition. Low O2 atmospheres caused a decrease in CO2 production and an increase in lactate concentration and LDH activity compared to air. By day 2, CO2 production rate decreased 0.4- and 0.5-fold, lactate increased 3.5- and 2.2-fold, and LDH activity increased 2.3- and 1.7-fold in carrot shreds stored in 0.5% and 2% O2, respectively, compared to samples in air. Based on nondenaturing electrophoresis, LDH isozyme composition analysis revealed five bands consisting of a tetrameric enzyme with subunits encoded by two different Ldh genes. Changes in staining intensity of the isozymes indicated that the increase in LDH activity in carrots under low O2 atmospheres resulted from increased enzyme synthesis and that there was preferential induction of one Ldh gene. These results suggest that lactic acid fermentation may be accelerated more under 0.5% than 2% O2 atmospheres due to greater expression of the Ldh genes.

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Hisashi Kato-Noguchi and Yukitoshi Tanaka

The allelopathic potential of Citrus junos Tanaka waste from food processing industry after juice extraction was investigated under laboratory conditions. C. junos waste powder inhibited the growth of roots and shoots of alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), crabgrass (Digitaria sanguinalis L.), timothy (Phleum pratense L.) and ryegrass (Lolium multiflorum Lam.). Significant reductions in the growth of roots and shoots were observed as the powder concentration increased. The concentration of abscisic acid-β-d-glucopyranosyl ester (ABA-GE) in C. junos waste was determined to be 17.9 mg · kg–1 dry weight. Its concentration in C. junos waste appears to account mostly for the observed inhibition of tested plant seedlings. These results indicate that C. junos waste is allelopathic with potential for use in agriculture to suppress weed emergence, which should be investigated further in the field.

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Hisashi Kato-Noguchi and Alley E. Watada

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Hisashi Kato-Noguchi and Alley E. Watada

Although a number of studies have been conducted to evaluate the effect of control and modified atmosphere on the quality and storability of carrot roots (Daucus carota L.) under low O2 atmosphere, little is known about the underling biochemical changes in particular changes in anaerobic respiration. Carrot root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2), or air for 7 days at 5 and 15°C to study the regulation of glycolysis and the accumulation of glycolytic end products, such as ethanol and/or lactic acid. Low O2 atmosphere caused increases in the concentrations of ethanol and acetaldehyde and the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC). By day 3, ethanol increased 38-, 25-, 13-, and 9.5-fold, acetaldehyde increased 20-, 13-, 7.7-, and 5.6-fold, ADH increased 7.6-, 6.3-, 3.8-, and 2.7-fold, and PDC increased 4.2-, 3.9-, 2.3-, and 2.2-fold for 0.5% O2 at 15 and 5°C, 2% O2 at 15 and 5°C, respectively, compared with corresponding air control. These results shows that the production of ethanol was higher in 0.5% O2 than in 2% O2 at both temperatures. The enhancement of the glycolytic flux under 0.5% O2 indicates that under these conditions the mitochondrial terminal oxydases were restricted, hence, the enhancement of ethanol synthesis, to compensate partly for the decrease in ATP production.

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Hisashi Kato-Noguchi and Alley E. Watada

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or in air for 7 days at 5 and 15 °C to study the regulation of ethanolic fermentation metabolism. Low-O2 atmospheres of 0.5% and 2% caused increases in ethanol and acetaldehyde concentrations and the activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) compared to air. By day 3, ethanol increased 38-, 25-, 13-, and 9.5-fold; acetaldehyde increased 20-, 13-, 7.7-, and 5.6-fold; ADH increased 7.6-, 6.3-, 3.8-, and 2.7-fold; and PDC increased 4.2-, 3.9-, 2.3-, and 2.2-fold in samples at 0.5% O2 at 15 or 5 °C and at 2% O2 at 15 or 5 °C, respectively, compared with corresponding samples in air. These results indicate that ethanolic fermentation was accelerated more in the 0.5% than in the 2% O2 atmosphere and more at 15 °C than at 5 °C. The acceleration of ethanolic fermentation may allow production of some ATP, which may permit the carrot tissues to survive.

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Hisashi Kato-Noguchi and Alley E. Watada

Carrot (Daucus carota L.) shreds were stored under a continuous flow of air or 0.5% and 2% O2 (balance N,) for 9 days at 5 and 15C. The resulting changes in respiration, levels of glycolytic intermediates, and activities of ATP: phosphofructo kinase (ATP-PFK), and PPi: phosphofructokinase (PPi-PFK) were monitored. Carrots under low O atmosphere exhibited an increase in RQ due to a greater reduction in 02 consumption than in CO2 production, and the increase in RQ was greater at 0.5% than at 2% O2 at both temperatures. Fructose 1,6-bisphosphate (F1,6P) accumulated with decreased O2 atmosphere and was 2-fold greater at 0.5% than at 2% O2 atmosphere at both temperatures. The levels of other glycolytic intermediates were not significantly influenced by low O2. The increase in PPi-PFK activity occurred at the same time as F1,6P accumulation. A similar relationship was not found with ATP-PFK. These results suggest that PPi-PFK may be involved in regulation of glycolysis under low O2 atmosphere.

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Hisashi Kato-Noguchi and Alley E. Watada

This study was undertaken to determine the effect of low-O2 atmosphere on the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), which can activate the enzyme pyrophosphate-dependent:phosphofructokinase (PPi-PFK) to catalyze the reaction from fructose 6-phosphate to fructose 1,6-bisphosphate (Fru-1,6-P2). Fru-2,6-P2 remained unchanged in carrot (Daucus carota L.) root shreds stored under air, but it increased 3.0- and 5.3-fold at 2% and 0.5% O2 atmosphere, respectively, at 5C, and the increases were almost twice as great at 15C. The concentration of PPi ranged from 17 to 33 nmol·g-1 fresh weight, which is more than sufficient for the PPi-PFK to proceed. Thus, low-O2 atmosphere appeared to hasten glycolysis of carrot shreds by increasing Fru-2,6-P2, which activated PPi-PFK toward glycolysis.