Endogenous peroxide levels in pear fruit (Pyrus communis) were measured using a titanium assay method, and were found to increase during senescence in both Bartlett and Bosc varieties. Application of glycolic acid or xanthine, serving as substrates for the formation of H2O2, increased the peroxide content of the tissue and accelerated the onset of ripening, as measured by increased softening and ethylene evolution. Application of ethylene also induced increased peroxide levels. Ripening processes were similarly promoted when peroxides were conserved by inhibiting the activity of catalase with hydroxylamine or potassium cyanide. By comparison, the inhibition of glycolate oxidase with alphahydroxy-2-pyridinemethanesulfonic acid decreased the peroxide content of the tissue and delayed the onset of ripening. These results indicate that the onset of ripening correlates with the peroxide content of fruit tissues as occurring under normal conditions or as influenced by the treatments. Hydrogen peroxide may be involved in oxidative processes required in the initiation and the promotion of ripening.

Involvement of hydrogen peroxide in the regulation of senescence in pear.

Endogenous peroxide levels in pear fruit (Pyrus communis) were measured using a titanium assay method, and were found to increase during senescence in both Bartlett and Bosc varieties. Application of glycolic acid or xanthine, serving as substrates for the formation of H202, increased the peroxide content of the tissue and accelerated the onset of ripening, as measured by increased softening and ethylene evolution. Application of ethylene also induced increased peroxide levels. Ripening processes were similarly promoted when peroxides were conserved by inhibiting the activity of catalase with hydroxylamine or potassium cyanide. By comparison, the inhibition of glycolate oxidase with alphahydroxy-2-pyridinemethanesulfonic acid decreased the peroxide content of the tissue and delayed the onset of ripening. These results indicate that the onset of ripening correlates with the peroxide content of fruit tissues as occurring under normal conditions or as influenced by the treatments. Hydrogen peroxide may be involved in oxidative processes required in the initiation and the promotion of ripening.

Involvement of Hydrogen Peroxide in the Regulation of

The insoluble cell wall polymers of cultured spinach cells contained esterified ferulic acid at 2–5 mg g-1 dry weight. Gibberellic acid (GA3, 10-11–10-6 M) promoted the expansion of these cells and simultaneoulsy suppressed peroxidase secretion, reduced the activity of cellular phenylanine ammonia-lyase and favoured the accumulation of wall-esterified ferulate and of extracellular soluble phenolic aglycones. When growth was prevented with 0·7 M sorbitol, GA3 still evoked the phenolic and peroxidase effects. It is suggested that peroxidase restricts growth by rigidifying the cell wall in two ways: (a) covalently by catalysing the conversion of feruloyl side-chains into diferuloyl cross-links and (b) non-covalently by catalysing the conversion of soluble phenolics into hydrophobic quinones (or polymers). GA3 is hypothesised to prevent this rigidification by inhibiting peroxidase secretion.

Phonolic components of the primary cell wall and their possible rôle in the hormonal regulation of growth.

Biosynthesis and Metabolism of Plant Hormones

This chapter summarises the vast literature on the composition* of green coffee beans paying particular attention to those components which are peculiar to coffee. The corresponding data are given for roasted beans and where possible for soluble powders. Attention is focused on compositional factors that might be determinants of acceptability, and situations where the data are incomplete or contradictory with the intention of provoking thought, comment and further investigation.

Chemical and Physical Aspects of Green Coffee and Coffee Products

Commercial horseradish peroxidase, when supplemented with dichlorophenol and either manganese or hydrogen peroxide, will rapidly oxidize glutathione. This peroxidase-catalyzed oxidation of glutathione is completely inhibited by the presence of auxin protectors. Three auxin protectors and three o-dihydroxyphenols were tested; all inhibited the oxidation. Glutathione oxidation by horseradish peroxidase in the presence of dichlorophenol and Mn is also completely inhibited by catalase, implying that the presence of Mn allows the horseradish peroxidase to reduce oxygen to H2O2, then to use the H2O2 as an electron acceptor in the oxidation of glutathione. Catalase, added 2 minutes after the glutathione oxidation had begun, completely inhibited further oxidation but did not restore any gluthathione oxidation intermediates. In contrast, the addition of auxin protectors, or o-dihydroxyphenols, not only inhibited further oxidation of gluthathione by horseradish peroxidase (+ dichlorophenol + Mn), but also caused a reappearance of glutathione as if these antioxidants reduced a glutathione oxidation intermediate. However, when gluthathione was oxidized by horseradish peroxidase in the presence of dichlorophenol and H2O2 (rather than Mn), then the inhibition of further oxidation by auxin protectors or o-dihydroxyphenols was preceded by a brief period of greatly accelerated oxidation. The data provide further evidence that auxin protectors are cellular redox regulators. It is proposed that the monophenol-diphenol-peroxidase system is intimately associated with the metabolic switches that determine whether a cell divides or differentiates.

Studies on Auxin Protectors XI. Inhibition of Peroxidase-Catalyzed Oxidation of Glutathione by Auxin Protectors and o-Dihydroxyphenols

Protector-II (Pr-II) of the Japanese morning glory (Pharbitis nil Choisy) was inactivated by exposure to polyphenol oxidase. An unidentified protector in the same molecular weight range obtained from sunflower was also inactivated by this enzyme. Earlier speculations that protectors might be lipoprotein in nature were negated by the fact that neither lipase nor protease inactivated the protectors. The protectors were also not inactivated by incubating with alpha-amylase, DNase, or RNase. Catechol mimics Pr and is inactivated by polyphenol oxidase. The oxidation of catechol to o-quinone is accompanied by a loss of chromophores that absorb ultraviolet light and the appearance of a reddish brown color. Similarly, when the relatively low molecular weight auxin protectors (Pr-II class) were incubated with polyphenol oxidase, their oxidation was also frequently associated with the formation of brown color, and oxidation with H(2)O(2) caused a loss of ultraviolet-absorbing chromophores. The data indicate that auxin protectors contain o-dihydroxyphenolic groups at their active site.That o-dihydroxyphenols inhibit indoleacetic acid oxidation has been demonstrated by numerous workers. It is suggested that the high molecular weight auxin protectors and the phenolic compounds described by other authors comprise part of a metabolic system concerned with the regulation of peroxidase-catalyzed redox reactions.

/pdf/studies-on-auxin-protectors-ix-inactivation-of-certain-pl81ld39ve.pdf

Studies on Auxin Protectors: IX. Inactivation of Certain Protectors by Polyphenol Oxidase

Auxin protectors completely inhibit the peroxidase-catalyzed oxidation of indoleacetic acid (IAA). Presumably only when the protector substance itself has been oxidized, does IAA oxidation begin. Reduced nicotinamide-adenine dinucleotide (NADH) mimics the native auxin protectors: In the presence of NADH, the peroxidase-catalyzed oxidation of IAA does not begin until almost all the NADH has been oxidized.



Auxin protectors slow the oxidation of NADH in the presence of the peroxidase complex (enzyme plus manganese). However, in the absence of the peroxidase complex, protectors actually accelerate the spontaneous oxidation of NADH. Protectors can also accelerate the oxidation of the dye 2,6-dichlorophenol-indophenol, especially in the presence of manganese. Protector oxidized by boiling with traces of hydrogen peroxide will act as an electron acceptor in the peroxidase-catalyzed oxidation of NADH. The reversible redox role of auxin protectors implies that they can act as cellular poisers.

Studies of Auxin Protectors VIII. Evidence that Auxin Protectors Act as Cellular Poisers

The lignification and differentiation of phloem fibers in sunflower stems is inhibited by growing crown gall tumors. Crown gall tumor tissue has previously been shown to contain large quantities of auxin protectors. Since auxin protectors are antioxidants which inhibit peroxidase-catalyzed reactions, and since the formation of lignin is known to involve a peroxidase-catalyzed reaction, an investigation was undertaken to examine the relationship between auxin protectors and lignification in sunflower crown gall tissue.



Sunflower crown gall tissue placed into media low in mineral content, rapidly lignifies. In the low mineral media, protectors appear in the medium within an hour or two, implying that endogenously-synthesized protectors rapidly leak out of the tissue. In control media, the tissue neither lignified appreciably, nor did it exhibit an excessive amount of protector release. The addition of Ca2+ to the low mineral medium markedly slowed, but did not entirely prevent lignification; similarly Ca2+ markedly slowed the release of protector into the low mineral medium. Auxin protectors added to the low mineral medium did not inhibit lignification apparently because, in the medium, the protectors are rapidly oxidized to quinones. The addition of catechol, a substance which mimics protector, also failed to inhibit lignification and also formed a colored compound in the medium suggesting o-qui none formation. In contrast, dithiothreitol, a strong anti-oxidant which upon oxidation does not form a strong oxidant (such as o-quinone), when added to the low mineral medium does inhibit lignification.



It is suggested that in the in vitro situation lignification and senescence occurs in low mineral media because the protectors leak out rapidly causing the cell's metabolism to favor peroxidase-catalyzed oxidations including those leading to lignification, while in the in vivo situation the excess protectors produced by crown gall tumor tissue diffuse into surrounding tissue, maintaining a reduced state in such tissues and thereby inhibiting differentiation and lignification. The synthesis of large quantities of protectors by the tumor tissue therefore could account for the anaplasia of the bundle caps observed in sunflower internodes in the vicinity of growing crown gall tumors.

Studies on Auxin Protectors X. Protector Levels and Lignification in Sunflower Crown Gall Tissue

This study examined the physical and biogeochemical processes that determine the spatial and summer/winter distributions of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in the Taiwan Strait (TS). The hydrological conditions in the TS varied between early summer and winter because of differences in terrestrial input as well as input from the poleward South China Sea Water (SCSW) during the warm summer and the strong, nutrient-rich, equatorward China Coastal Water (CCW) in winter. Concentrations of dissolved organic carbon (DOC) ranged from 60 to 100 μM-C in early summer and from 70 to 144 μM-C in winter. The average stoichiometric ratio of DOC : DON:DOP was high (353:49:1) in the land-source impacted zones and low (168:21:1) in the SCSW-laden areas, both of which are higher than the Redfield ratio. The concentrations of DOC and nutrients were higher in the western TS (on the coast of China) than in the eastern TS (on the coast of Taiwan), and the highest concentrations were mostly found in the Minjiang River plume, reflecting the profound effects of freshwater input in early summer and CCW inflow in winter. The absorption and emission characteristics of the CDOM varied to a large extent with locations because of the mixing of the shelf water with different source waters. Although the absorption coefficient (aCDOM(325)) and fluorescence intensity of the terrestrial humic-like CDOM (Ft: Ex/Em= 260/400-460) were both strongly inversely correlated with salinity, as an optical tracer, Ft may be more effective than aCDOM(325) in examining the mixing among source waters, given that aCDOM(325) may be subject to various photobleaching effects in the TS. Ft was also significantly correlated with the concentrations of terrestrially derived nitrate and nitrite (N+N) and silicate. The results of factor analysis elucidated the complexity of the hydrological and biological processes that affect the distributions of DOM and CDOM in the TS. Graphical Abstract

/pdf/biophysical-controls-on-spatial-and-summer-winter-310jm8yb.pdf

Hsin-Mei Yang

Papers

Studies on Auxin Protectors XI. Inhibition of Peroxidase-Catalyzed Oxidation of Glutathione by Auxin Protectors and o-Dihydroxyphenols

Studies on Auxin Protectors: IX. Inactivation of Certain Protectors by Polyphenol Oxidase

Studies of Auxin Protectors VIII. Evidence that Auxin Protectors Act as Cellular Poisers

Studies on Auxin Protectors X. Protector Levels and Lignification in Sunflower Crown Gall Tissue

Biophysical controls on spatial and summer/winter distributions of total and chromophoric dissolved organic matter in the Taiwan Strait