Biomedical subjects

S O Duke

Publications and source records attributed to S O Duke.

29 records · Page 2Linked to original sources

PubMed1985

Effects of Acifluorfen on Endogenous Antioxidants and Protective Enzymes in Cucumber (Cucumis sativus L.) Cotyledons.

The herbicide acifluorfen (2-chloro-4-(trifluoromethyl)phenoxy-2-nitrobenzoate) causes strong photooxidative destruction of pigments and lipids in sensitive plant species. Antioxidants and oxygen radical scavengers slow the bleaching action of the herbicide. The effect of acifluorfen on glutathione and ascorbate levels in cucumber (Cucumis sativus L.) cotyledon discs was investigated to assess the relationship between herbicide activity and endogenous antioxidants. Acifluorfen decreased the levels of glutathione and ascorbate over 50% in discs exposed to less than 1.5 hours of white light (450 microeinsteins per square meter per second). Coincident increases in dehydroascorbate and glutathione disulfide were not observed. Acifluorfen also caused the rapid depletion of ascorbate in far-red light grown plants which were photosynthetically incompetent.Glutathione reductase, dehydroascorbate reductase, superoxide dismutase, ascorbate oxidase, ascorbate free radical reductase, peroxidase, and catalase activities rapidly decreased in acifluorfen-treated tissue exposed to white light. None of the enzymes were inhibited in vitro by the herbicide. Acifluorfen causes irreversible photooxidative destruction of plant tissue, in part, by depleting endogenous antioxidants and inhibiting the activities of protective enzymes.

Journal Article↗

PubMed1983

Differential light induction of nitrate reductases in greening and photobleached soybean seedlings.

Soybean (Glycine max [L.] Merr.) seeds were imbibed and germinated with or without NO(3) (-), tungstate, and norflurazon (San 9789). Norflurazon is a herbicide which causes photobleaching of chlorophyll by inhibiting carotenoid synthesis and which impairs normal chloroplast development. After 3 days in the dark, seedlings were placed in white light to induce extractable nitrate reductase activity. The induction of maximal nitrate reductase activity in greening cotyledons did not require NO(3) (-) and was not inhibited by tungstate. Induction of nitrate reductase activity in norflurazon-treated cotyledons had an absolute requirement for NO(3) (-) and was completely inhibited by tungstate. Nitrate was not detected in seeds or seedlings which had not been treated with NO(3) (-). The optimum pH for cotyledon nitrate reductase activity from norflurazon-treated seedlings was at pH 7.5, and near that for root nitrate reductase activity, whereas the optimum pH for nitrate reductase activity from greening cotyledons was pH 6.5. Induction of root nitrate reductase activity was also inhibited by tungstate and was dependent on the presence of NO(3) (-), further indicating that the isoform of nitrate reductase induced in norflurazon-treated cotyledons is the same or similar to that found in roots. Nitrate reductases with and without a NO(3) (-) requirement for light induction appear to be present in developing leaves. In vivo kinetics (light induction and dark decay rates) and in vitro kinetics (Arrhenius energies of activation and NADH:NADPH specificities) of nitrate reductases with and without a NO(3) (-) requirement for induction were quite different. K(m) values for NO(3) (-) were identical for both nitrate reductases.

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PubMed1983

Immunocytochemical and Cytochemical Localization of Photosystems I and II.

Cytochemical and immunocytochemical methods were used to localize photosystems I and II in barley (Hordeum vulgare L. cv Himalaya) chloroplasts. PSI activity, monitored by diaminobenzidine oxidation, was associated with the lumen side of the thylakoids of both grana and stroma lamellae. The P(700) chlorophyll a protein, the reaction center of PSI, was localized on thin sections of barley chloroplasts using monospecific antibodies to this protein and the peroxidase-antiperoxidase procedure. Results obtained by immunocytochemistry were similar to those of the diaminobenzidine oxidation: both grana and stroma lamellae contained immunocytochemically reactive material. Both the grana and stroma lamellae were also labeled when isolated thylakoids were reacted with the P(700) chlorophyll a protein antiserum and then processed by the peroxidase-antiperoxidase procedure. PSII activity was localized cytochemically by monitoring the photoreduction of thiocarbamyl nitroblue tetrazolium, a reaction sensitive to the PSII inhibitor, DCMU. PSII reactions occurred primarily on the grana lamellae, with weaker reactions on the stroma lamellae.

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PubMed1982

Ultrastructural localization of urate oxidase in nodules of Sesbania exaltata, Glycine max, and Medicago sativa.

The localization of urate oxidase (=uricase, E.C. 1.7.3.3) was determined cytochemically in nodules of Sesbania exaltata (Raf.) Cory, soybean (Glycine max [L.] Merr.) and alfalfa (Medicago sativa [L.] ), using the precipitation of peroxide (produced during the oxidation of urate) by cerium chloride. Cerium perhydroxide reaction product was noted only in the microbodies, a localization consistent with biochemical fractionation studies on urate oxidase. Urate oxidase was present not only in the uninfected cells of the cortical tissue, but also in both infected and interstitial cells in the central tissue, suggesting that at least this enzyme of ureide metabolism is not confined to interstitial cells. Urate oxidase cytochemistry of nodules from alfalfa (Medicago sativa L.), an amide producer, also resulted in microbody staining but the microbodies were infrequently noted in cell profiles.

Fabaceae↗

PubMed1981

Cytochemical localization of photosystem II donor sites.

Tetramethylbenzidene, an artificial donor of electrons to the photosystem (PS) II reaction center, is oxidized to an osmiophilic polymer that allows for the localization of the donor site of PS II. Mesophyll chloroplasts of Sorghum bicolor (L.) Moench. contain 0.1-0.2 micron deposits only in the grana stacks and on the lumen side of the thylakoid. Agranal mature bundle sheath plastids (known to be devoid of PS II activity) show little deposition and the products appear randomly distributed along the lamellae. The cytochemical localization of PS II donor sites on the lumen side is consistent with flash photolysis and diaminobenzenesulfonic acid inactivation studies as well as the chemiosmotic theory for the generation of a proton gradient.

Benzidines↗

PubMed1981

Histochemical localization of nitrate reductase.

NADH-dependent nitrate reductase (E.C. 1.6.6.1) was ultrastructurally localized in norflurazon-treated and control soybean cotyledons [Glycine max (L.) Merr.] by a method based upon the increase in osmiophilia due to the formation of an azo dye. The reaction product was observed in small vesicles throughout the cytoplasm. An apparent transport of nitrite to the plastid, the site of nitrite reduction, may occur through fusion of the nitrite-containing vesicles with the chloroplast envelope. Plants grown in tungstate lacked nitrate reductase activity as measured by standard assay procedures, and showed no increase in osmiophilia, suggesting a degree of specificity of this cytochemical procedure.

Herbicides↗

PubMed1980

Effects of Glyphosate on Metabolism of Phenolic Compounds: V. l-alpha-AMINOOXY-beta-PHENYLPROPIONIC ACID AND GLYPHOSATE EFFECTS ON PHENYLALANINE AMMONIA-LYASE IN SOYBEAN SEEDLINGS.

The phenylalanine ammonia-lyase (PAL) inhibitor l-alpha-aminooxy-beta-phenylpropionic acid (AOPP) was root-fed to light-exposed soybean seedlings alone or with glyphosate [N-(phosphonomethyl)glycine] to test further the hypothesis that PAL activity is involved in the mode of action of glyphosate. Extractable PAL activity was increased by 0.01 and 0.1 millimolar AOPP. AOPP reduced total soluble hydroxyphenolic compound levels and increased phenylalanine and tyrosine levels, indicating that in vivo PAL activity was inhibited by AOPP. The increase in extractable PAL caused by AOPP may be a result of decreased feedback inhibition of PAL synthesis by cinnamic acid and/or its derivatives. AOPP alone had no effect on growth (fresh weight and elongation) at either concentration, but at 0.1 millimolar it slightly alleviated growth (fresh weight) inhibition caused by 0.5 millimolar glyphosate after 4 days. Reduction of the free pool of phenylalanine by glyphosate was reversed by AOPP. These results indicate that glyphosate exerts some of its effects through reduction of aromatic amino acid pools through increases in PAL activity and that not all growth effects of glyphosate are due to reductions of aromatic amino acids.

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PubMed1978

Effects of Irradiance during Growth on Adaptive Photosynthetic Characteristics of Velvetleaf and Cotton.

We grew velvetleaf (Abutilon theophrasti Medic.) and cotton (Gossypium hirsutum L. var. Stoneville 213) at three irradiances and determined the photosynthetic responses of single leaves to a range of six irradiances from 90 to 2000 mueinsteins m(-2)sec(-1). In air containing 21% O(2), velvetleaf and cotton grown at 750 mueinsteins m(-2)sec(-1) had maximum photosynthetic rates of 18.4 and 21.9 mg of CO(2) dm(-2)hr(-1), respectively. Maximum rates for leaves grown at 320 and 90 mueinsteins m(-2)sec(-1) were 15.3 and 10.3 mg of CO(2) dm(-2)hr(-1) in velvetleaf and 12 and 6.7 mg of CO(2) dm(-2)hr(-1) in cotton, respectively. In 1 O(2), maximum photosynthetic rates were 1.5 to 2.3 times the rates in air containing 21% O(2), and plants grown at medium and high irradiance did not differ in rate. In both species, stomatal conductance was not significantly affected by growth irradiance. The differences in maximum photosynthetic rates were associated with differences in mesophyll conductance. Mesophyll conductance increased with growth irradiance and correlated positively with mesophyll thickness or volume per unit leaf area, chlorophyll content per unit area, and photosynthetic unit density per unit area. Thus, quantitative changes in the photosynthetic apparatus help account for photosynthetic adaptation to irradiance in both species. Net assimilation rates calculated for whole plants by mathematical growth analysis were closely correlated with single-leaf photosynthetic rates.

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PubMed1977

Model for variable light sensitivity in imbibed dark-dormant seeds.

The level of light-induced germination of the seed of common purslane (Portulaca oleracea L.) and curly dock (Rumex crispus L.) changes with dark incubation time prior to brief, low energy, red light treatment. The rate at which phytochrome-far red-absorbing form (Pfr) acts in the light-induced population of seeds was measured by quantitating per cent reversals of the red light effect with saturating far red light exposures at successive times after the red light exposure. A linear positive correlation was found between this rate and the final germination level. These results are compatible with a model involving changing levels, during dark incubation, of a component with which Pfr interacts. In this model, germination is initiated after attainment of a certain level of interaction between Pfr and this component. These findings also support the view that the Pfr to Pr decay rate constant and total phytochrome level are stable during dark incubation.

Journal Article↗

PubMed1976

Photosynthetic Independence of Light-induced Anthocyanin Formation in Zea Seedlings.

Results are reported which support the view that the photosynthetic photosystems are not involved in the high irradiance response (HIR) phenomenon of light-dependent anthocyanin biosynthesis in dark-grown Zea mays L. seedlings. A negative correlation between change in greening rates and change in light-dependent anthocyanin accumulation rates with age was demonstrated. Lack of chlorophyll synthesis in a strain of maize possessing a temperature-sensitive lesion for chlorophyll synthesis could not be correlated with light-induced anthocyanin accumulation. Furthermore, seedlings totally lacking photosynthetic capabilities, either due to a genetic lesion or to excision of all photosynthetic tissue, had an enhanced rate of photoinduced anthocyanin formation. This evidence indicates that the HIR results in the initiation of processes that are in competition with chloroplast development for substrate in normal, intact seedlings.

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PubMed1969

Zea shoot development in response to red light interruption of the dark-growth period. I. Inhibition of first internode elongation.

Brief, low energy (approximately 400 Kerg cm(-2)) red light interruption of the early dark-growth period of Zea mays L. cv F-M Cross induced inhibition of first internode elongation which was maximal whenever light interruption occurred from 2.5 to 4 days of seedling age. Two-thirds of the maximal inhibition occurred in the tissues constituting the region 0 to 2 mm below the coleoptilar node at time of light treatment. The coleoptile tip showed the greatest sensitivity for red light reception in the internode response. Far-red light exposures following red light treatments reversed the red light effect. However, far-red light alone inhibited first internode elongation as effectively as red light of similar dosage.

Journal Article↗