Gibberellin Relationships in Zinc-Deficient Plants

The content of gibberellin-like substances was reduced to aboutone seventh in maize and one half in barley and oat plants grownunder zinc-deficient conditions compared with control plantsgrown with sufficient zinc nutrition. The supplement of zincto zinc-deficient maize plants not only recovered their growthbut also increased contents of gibberellin-like substances.The growth cessation in zinc-deficient plants is discussed inrelation to the endogenous contents of gibberellin. (Received March 12, 1986; Accepted May 28, 1986)     

Superoxide Dismutase in Plants

Superoxide dismutases (SODs) are metal-containing enzymes that catalyze the dismutation of superoxide radicals to oxygen and hydrogen peroxide. The enzyme has been found in all aerobic organisms examined where it plays a major role in the defense against toxic-reduced oxygen species, which are generated as byproducts of many biological oxidations. The generation of oxygen radicals can be further exacerbated during environmental adversity and consequently SOD has been proposed to be important for plant stress tolerance. In plants, three forms of the enzyme exist, as classified by their active site metal ion: copper/zinc, manganese, and iron forms. The distribution of these enzymes has been studied both at the subcellular level and at the phylogenic level. It is only in plants that all three different types of SOD coexist. Their occurrence in the different subcellular compartments of plant cells allows a study of their molecular evolution and the possibility of understanding why three functionally equivalent but structurally different types of SOD have been maintained. Several cDNA sequences that encode the different SODs have recently become available, and the use of molecular techniques have greatly increased our knowledge about this enzyme system and about oxidative stress in plants in general, such that now is an appropriate time to review our current knowledge.     

Decreased Production of the Superoxide Anion Radical in Neutrophils Exposed to a Near-Null Magnetic Field

Biophysics - This paper reports that pre-incubation of a neutrophil suspension in the presence of a near-null magnetic field produced using a system of magnetic shields (a residual constant...     

Evidence for the Involvement of Loosely Bound Plastosemiquinones in Superoxide Anion Radical Production in Photosystem II

Recent evidence has indicated the presence of novel plastoquinone-binding sites, Q_C and Q_D, in photosystem II (PSII). Here, we investigated the potential involvement of loosely bound plastosemiquinones in superoxide anion radical (O₂^•−) formation in spinach PSII membranes using electron paramagnetic resonance (EPR) spin-trapping spectroscopy. Illumination of PSII membranes in the presence of the spin trap EMPO (5-(ethoxycarbonyl)-5-methyl-1-pyrroline N-oxide) resulted in the formation of O₂^•−, which was monitored by the appearance of EMPO-OOH adduct EPR signal. Addition of exogenous short-chain plastoquinone to PSII membranes markedly enhanced the EMPO-OOH adduct EPR signal. Both in the unsupplemented and plastoquinone-supplemented PSII membranes, the EMPO-OOH adduct EPR signal was suppressed by 50% when the urea-type herbicide DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) was bound at the Q_B site. However, the EMPO-OOH adduct EPR signal was enhanced by binding of the phenolic-type herbicide dinoseb (2,4-dinitro-6-sec-butylphenol) at the Q_D site. Both in the unsupplemented and plastoquinone-supplemented PSII membranes, DCMU and dinoseb inhibited photoreduction of the high-potential form of cytochrome b₅₅₉ (cyt b₅₅₉). Based on these results, we propose that O₂^•− is formed via the reduction of molecular oxygen by plastosemiquinones formed through one-electron reduction of plastoquinone at the Q_B site and one-electron oxidation of plastoquinol by cyt b₅₅₉ at the Q_C site. On the contrary, the involvement of a plastosemiquinone formed via the one-electron oxidation of plastoquinol by cyt b₅₅₉ at the Q_D site seems to be ambiguous. In spite of the fact that the existence of Q_C and Q_D sites is not generally accepted yet, the present study provided more spectroscopic data on the potential functional role of these new plastoquinone-binding sites.     

Spin-Trapping of the Superoxide Radical in Aprotic Solvents

The superoxide adduct of 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) has been detected by EPR spectroscopy in aprotic solvents using KO₂ solubilized in 18-crown-6-ether as a source of superoxide. The EPR hyperfine splitting constants of the DMPO-superoxide adduct were as follows: benzene/toluene (a_N = 12.65 G; a^β_β = 10.4G; a_γ = 1.3G); heptane (a_N = 12.49G; a_β^β = 10.29G; a^γ_H = 1.2g); and acetone (a_N = 12.6G; a_β^β = 10.17 G; a_γ = 1.3 G). The EPR parameters for benzene, toluene and heptane differ significantly from previously reported values. A plot of the hyperfine splitting constants for the DMPO superoxide adduct as a function of solvent polarity (Kosower Z value) indicates that while a_N and a_β^β both decrease by about 1 G on going from water to ethanol, further decreases in polarity do not greatly affect these EPR parameters.     

Superoxide Radical Generation by Amadori Compounds

Several D-sugars were incubated with L-lysine or with L-arginine for 10 days. The resulting compounds are able to reduce nitrobluetetrazolium (NBT). This is prevented by superoxide dismutase (SOD), indicating that the superoxide radical is generated by the resulting Amadori compounds.

The formation of superoxide radical in vivo, as a result of nonenzymatic glycosylation of proteins, may be considered to be a contributory factor to the appearance of chronic complications of diabetes.     

Superoxide Radical Generation by Amadori Compounds

Several D-sugars were incubated with L-lysine or with L-arginine for 10 days. The resulting compounds are able to reduce nitrobluetetrazolium (NBT). This is prevented by superoxide dismutase (SOD), indicating that the superoxide radical is generated by the resulting Amadori compounds.

The formation of superoxide radical in vivo, as a result of nonenzymatic glycosylation of proteins, may be considered to be a contributory factor to the appearance of chronic complications of diabetes.     

Influence of Hyperthyroidism on Superoxide Radical and Hydrogen Peroxide Production by Rat Liver Submitochondrial Particles

Administration of daily doses of 0.1 mg of 3, 5, 3'-triiodothyronine (T₃)/kg body weight for 3 consecutive days to fed rats elicited a calorigenic response in the animals, in concomitance with a 36% increase in the rate of O₂ consumption by the liver. In these conditions, liver submitochondrial particles (SMP) from T₃-treated rats exhibited marked increases in the rate of superoxide radical generation, both in the presence of NADH (142%) or succinate (152%). Furthermore, liver SMP from hyperthyroid animals released hydrogen peroxide at higher rates than those of euthyroid rats, either under basal conditions or in the succinate-supported process, both in the absence and presence of antimycin-A. It is concluded that the hyperthyroid state in the rat leads to a drastic enhancement in the capacity of liver mitochondria to produce active oxygen species, which correlates with the elevated respiratory rate observed in the intact organ.     

Depolarization-Induced Superoxide Radical Formation in Rat Hippocampal Slices

Glutamate is the major excitatory neurotransmitter in the brain. Activation of glutamatergic receptors induces neuronal depolarization, and if this activation is excessive, it can lead to cellular damage. Evidence for the participation of glutamatergic receptor systems in the production of oxygen free radicals in neuronal cells is accumulating. In the present study, we have kept hippocampal slices under depolarization conditions induced by including 50 mM K⁺ in artificial cerebrospinal fluid (dACSF) and followed superoxide radical formation. Superoxide radical formation was increased in dACSF-incubated hippocampal slices. We have also attempted to determine the relative contribution of agonist- and voltage-sensitive channels to superoxide radical formation by using their selective blockers. Superoxide radical formation was suppressed by MK 801, memantine, APV, CNQX, and TTX application to dACSF-incubated hippocampal slices. Similar studies on different experimental systems may help to unravel the underlying critical events and active mechanisms that may lead to superoxide radical generation and subsequent neuronal cell death.     

The Roots of Carnivorous Plants

Carnivorous plants may benefit from animal-derived nutrients to supplement minerals from the soil. Therefore, the role and importance of their roots is a matter of debate. Aquatic carnivorous species lack roots completely, and many hygrophytic and epiphytic carnivorous species only have a weakly devel-oped root system. In xerophytes, however, large, extended and/or deep-reaching roots and sub-soil shoots develop. Roots develop also in carnivorous plants in other habitats that are hostile, due to flood-ing, salinity or heavy metal occurance. Information about the structure and functioning of roots of car- nivorous plants is limited, but this knowledge is essential for a sound understanding of the plants’ physiology and ecology. Here we compile and summarise available information on: (1) The morphology of the roots. (2) The root functions that are taken over by stems and leaves in species without roots or with poorly developed root systems; anchoring and storage occur by specialized chlorophyll-less stems; water and nutrients are taken up by the trap leaves. (3) The contribution of the roots to the nutrient supply of the plants; this varies considerably amongst the few investigated species. We compare nutrient uptake by the roots with the acquisition of nutri-ents via the traps. (4) The ability of the roots of some carnivorous species to tolerate stressful conditions in their habitats; e.g., lack of oxygen, saline conditions, heavy metals in the soil, heat during bushfires, drought, and flooding     

Accumulation of Superoxide Radical in Corn Leaves During Waterlogging

The changes in superoxide (O2-) production, hydrogen peroxide (H2O2) content and active oxygen scavenging system in corn (Zea mays L. ) leaves under waterlogging stress were investigated to explore the relationship between O2- accumulation and waterlogging injury. Corn plants were grown in pots in a controlled environment. The results showed that prolonged waterlogging treatment conducted at 4-leaf stage caused a significant increase in the production of O2- and H2O2, while the extent of O2- change was more than that of H2O2. Malondialdehyde (MDA) accumulation, chlorophyll loss and electrolye leakage were positively correlated with O2- production in corn waterlogged leaves. Foliage spraying with 0. 1 mmol/L paraquat (02- producer) at the start of waterlogging treatment led to a significant increase in 02-, H202 and MDA levels. The addition of DDTC (SOD activity inhibitor) aggravated 02- formation in waterlogged leaves. Waterlogging apperantly reduced the activities of SOD. catalase (CAT), ascorbate peroxidase (AP) and the concentrations of ascorbic acid (ASA) and glutathione (GSH). It was noted that the decline in SOD activity proceeded the diminishment of H2O2 scavengers in chloroplasts (i. e. AP, AsA and GSH). The present findings suggest that O2- is involved in waterlogging damage, and excessive accumulation of 02- is due to the reduced SOD activity.     

Overexpression of Superoxide Dismutase Protects Plants from Oxidative Stress (Induction of Ascorbate Peroxidase in Superoxide Dismutase-Overexpressing Plants)

Photosynthesis of leaf discs from transgenic tobacco plants (Nicotiana tabacum) that express a chimeric gene that encodes chloroplast-localized Cu/Zn superoxide dismutase (SOD+) was protected from oxidative stress caused by exposure to high light intensity and low temperature. Under the same conditions, leaf discs of plants that did not express the pea SOD isoform (SOD-) had substantially lower photosynthetic rates. Young plants of both genotypes were more sensitive to oxidative stress than mature plants, but SOD+ plants retained higher photosynthetic rates than SOD- plants at all developmental stages tested. Not surprisingly, SOD+ plants had approximately 3-fold higher SOD specific activity than SOD- plants. However, SOD+ plants also exhibited a 3- to 4-fold increase in ascorbate peroxidase (APX) specific activity and had a corresponding increase in levels of APX mRNA. Dehydroascorbate reductase and glutathione reductase specific activities were the same in both SOD+ and SOD- plants. These results indicate that transgenic tobacco plants that overexpress pea Cu/Zn SOD II can compensate for the increased levels of SOD with increased expression of the H2O2-scavenging enzyme APX. Therefore, the enhancement of the active oxygen-scavenging system that leads to increased oxidative stress protection in SOD+ plants could result not only from increased SOD levels but from the combined increases in SOD and APX activity.     

Oxidation Products of Kaempferol by Superoxide Anion Radical

Kaempferol (3,4',5,7-tetrahydroxyflavone) was oxidized by O₂^–to 4-hydroxyphenylglyoxylic acid and phloroglucinolcarboxylicacid as identified by UV spectroscopy and high-performance liquidchromatography. The molar yields of the two compounds on thebasis of kaempferol oxidation were 19% and 21%, respectively,at pH 8. In addition to these two products, a compound whichwas hydrolyzed to 4-hydroxybenzoic acid and an unidentifiedcompound was produced. (Received November 21, 1986; Accepted April 10, 1987)     

Gallocyanine as a Fluorogen for the Identification of NADPH-Dependent Production of Superoxide Anion Radical by Blood Cells

Russian Journal of Bioorganic Chemistry - The interaction of the oxazine dye gallocyanine with reactive oxygen ( $$^{\centerdot }{\text{O}}_{2}^{ - },$$ Н2О2) and halogen (HOCl) species...     

植物中超氧阴离子自由基测定方法的改进

通过对植物超氧阴离子自由基测定反应中动力学曲线的分析, 确定了最佳的反应介质、反应参数和羟胺浓度, 以三氯甲烷代替乙醚作为植物色素萃取试剂, 克服了植物超氧阴离子测定中存在的诸多问题, 提高了测定结果的准确性、重复性和可比性。     

Mitochondria as a Source of Superoxide Anion Radical in Human Platelets

The radical-producing activity of human platelets has been studied using the enhanced chemiluminescence method. It is shown that chemiluminescence of isolated platelets is observed only in the presence of lucigenin, a selective probe for superoxide anion; the luminescence is amplified many times upon the addition of NADH and NADPH, the substrates of oxidative chains. The chemiluminescence is not affected by diphenyliodonium, an inhibitor of NADPH oxidase, but it is inhibited in a dose-dependent manner by the oxidative phosphorylation uncouplers dinitrophenol and rotenone. Thus, a superoxide anion radical is the main free radical generated by platelets, and mitochondria are one of the superoxide anion radical sources in platelets.     

Soil Anti-Scouribility Enhanced by Plant Roots

The magnitude of soil anti-scouribility depends on the physical condition of the soil. Plant roots can greatly enhance soil stability and anti-erodibility. A scouring experiment of undisturbed soil was conducted to investigate the effects of roots on soil anti-scouribility and its distribution in the soil profile. At the end of each erosion test, plant roots were collected from soil samples and root surface area was calculated by means of a computer image analysis system (CIAS). Root surface area density (RSAD), the surface area of the roots per unit of soil volume, was related to soil anti-scouribility. More than 83% of root surface area was concentrated in the 0-30 cm soil layer. Soil anti-scouribility increased with an increase in RSAD and the value of intensified soil anti-scouribility (ΔAS) can be expressed by exponential equations, depending on the plant species. These equations were ΔAS=9.578 6 RSAD^0.8321 (R^2=0.951) for afforested Pinus tabulaeformis Carr.ΔAS=7.8087 RSAD^0.7894(R^2=0.974) for afforested Robinia pseudoacacia L., and ΔAS=9.256 6 RSAD^0.8707(R^2=0.899) for Bothriochloa ischemum L.