Ethane Evolution Research Articles

Microporous inorganic/organic hybrids via oxysilylation of a cubic symmetry nanobuilding block [(HMe<sub>2</sub>SiOSiO<sub>1.5</sub>)<sub>8</sub>] with R<i><sub>x</sub></i>Si(OEt)<sub>4−</sub><i><sub>x</sub></i>

The B(C6F5)3 catalyzed Piers-Rubinsztajn (oxysilylation) reaction of the cubic symmetry Q-cage [(HMe2SiOSiO1.5)8] with ethoxysilanes in hexane forms microporous 3-D networks coincident with ethane evolution. Slow drying provides monoliths whereas fast drying provides powders. The reaction is most efficient if initiated at 60°C for 5 min and then allowed to progress at ambient. The products offer high specific surface areas [SSAs > 700 m2/g, e.g. with Si(OEt)4], with micropores of 0.6–2.0 nm, mesopores of 2–40 nm, total pore volumes ≈ 0.5 cc/g, and thermal stabilities to 320°C. Changes in reaction conditions (times, solvent volumes, catalyst concentrations) do not significantly change product properties pointing to rapid and complete reaction as evidenced by the near absence of residual Si–H under all conditions for 1:1: Si–H:Si–OEt ratios. RSi(OEt)3 gives similar 3-D microporous gels. Smaller R groups give higher SSAs than those with large R groups; however, R = n-octyl is not porous. Rigid, bridged compounds [(EtO)3Si–R–Si(OEt)3] (R = phenyl, biphenyl) offer high SSAs whereas flexible bridges [R = (CH2)2 or 8] give reduced SSAs. All materials were characterized by FTIR, TGA, XRD and BET. XRD studies show periodicities suggesting some long range ordering as might be expected for reactions with cubic symmetry Q8 cages. However, the fast reaction rates likely generate kinetic rather than thermodynamic products that cannot be expected to exhibit high degrees of ordering. Gel affinities for specific organics were studied showing some preferential ability to absorb specific solvents for example the 1:1 OHS:vinylSi(OEt)3 gels were more selective for toluene than the 1:1 OHS:TEOS gels.

Substitution effect on phenalenyl backbone in the rate of organozinc catalyzed ROP of cyclic esters

A series of zinc complexes (1-6) supported by substituted phenalenyl ligands was synthesized by reacting the phenalenyl ligands with diethyl zinc under ethane evolution. The solid state structures of these complexes (1-6) were determined by single crystal X-ray crystallography. Furthermore, the organozinc complexes (4-6) were tested for the polymerization of cyclic esters as efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) in the presence of benzyl alcohol (BnOH) as initiator. Complex 4 exhibited remarkably higher rate of polymerization under identical reaction condition than complexes 5 and 6. The polymerization of ε-caprolactone produced polymer with narrow polydispersities (M(w)/M(n) = 1.06 to 1.22), while the polymerization of lactide monomers afforded polylactides with polydispersity values ranging from 1.08 to 1.8. The kinetic experiments unravelled a controlled polymerization. The controlled nature of polymerization was further utilized in the preparation of the block copolymer poly(CL)block-poly(rac-LA).

Mechanism of growth amelioration of NaCl-stressed rice (Oryza sativa L.) by .DELTA.-aminolevulinic acid

The mechanism of growth amelioration of NaCl-stressed rice (Oryza sativa L. cv. Nipponbare) by δ-aminolevulinic acid (ALA) was investigated. Rice growth recovered when plants were pretreated with 0.1 or 1 μM ALA before treatment with 50 mM NaCl. There was no increase in chlorophyll content by ALA treatment, indicating that the growth recovery was not due to increased chlorophyll content although ALA is a precursor of chlorophyll biosynthesis. The activities of antioxidative enzymes, including catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APx), and superoxide dismutase (SOD), increased with ALA treatment. In particular, stimulation of CAT, GR, and APx activities by ALA was significant. The hydrogen peroxide (H2O2) content decreased after ALA treatment under NaCl-stress conditions. Peroxidation of membrane lipids, as measured by ethane evolution, also decreased after ALA treatment. These results suggest that ALA induces growth amelioration in NaCl-stressed rice by stimulating antioxidative enzyme activity, which resulted in decreased reactive oxygen generation and lipid peroxidation.

Quinclorac-induced cell death is accompanied by generation of reactive oxygen species in maize root tissue

The importance of reactive oxygen species for herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid)-induced cell death in roots was investigated. This was in order to understand its mode of action in grass species grown in the dark. Under these dark conditions, quinclorac suppressed the shoot and root growth of maize ( Zea mays L. cv. Honey Bantam) in a concentration-dependent manner (⩽50 μM), although the inhibition level was less than that observed under growth conditions in the light. Analysis of cell viability using Evans blue or fluorescein diacetate–propidium iodide (FDA–PI) staining showed that the maize root cells significantly lost their viability after 14 h root treatment with 10 μM quinclorac, but not 10 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Determination of reactive oxygen species (ROS) in maize roots using a superoxide anion ( O 2 - )-specific indicator, dihydroethidium (DHE), indicated that 50 μM quinclorac induced a high level of O 2 - production in maize roots after 14 h root treatment than that of either the control (non-treated) or with 50 μM 2,4-D. Moreover, either cell death or ethane evolution, an indicator of lipid peroxide formation, in maize root segments was significantly enhanced by 50 μM quinclorac, but not by 50 μM 2,4-D. On the other hand, the 50 μM 2,4-D treatment induced much higher ethylene and cyanide production in the root segments than with the 50 μM quinclorac. These results suggest that quinclorac-induced cell death in maize roots may be caused by ROS and lipid peroxidation, but not by ethylene and its biosynthetic pathway-related substances including cyanide, which have been thought to be the causative factor of quinclorac-induced phytotoxicity in susceptible grass weeds such as Echinochloa, Digitaria, and Setaria.

Oxidative injury induced by the herbicide quinclorac on Echinochloa oryzicola Vasing. and the involvement of antioxidative ability in its highly selective action in grass species

To investigate the possible involvement of antioxidative ability in the highly selective action of the herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) in grass species, quinclorac-induced oxidative injuries and the activities of the antioxidative enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbic acid peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) were studied in tolerant rice ( Oryza sativa L. cv. Nipponbare) and a particularly susceptible grass weed, Echinochloa oryzicola Vasing. There were no significant differences in total chlorophyll content, formation of thiobarbituric acid-reactive substances (TBARS), and ethane and ethylene productions between 1 μM quinclorac-treated and control seedlings of rice both under continuous light and dark conditions. In contrast, the chlorophyll content in leaves decreased, and TBARS formation in shoots and ethane evolution increased in quinclorac-treated E. oryzicola seedlings under continuous light for 24 h. These changes were not observed in the dark, indicating that light enhanced the selective activity of quinclorac between rice and E. oryzicola. α-Tocopherol (α-TOH), a free radical scavenger, significantly suppressed quinclorac-induced TBARS formation in shoots and chlorophyll loss in the leaves of E. oryzicola. Antioxidant enzyme assays showed that the constitutive activities of SOD, CAT, APX, and GR enzymes in the shoots of E. oryzicola were lower than those in rice. Furthermore, there were significant correlations between the constitutive activities of APX and GR in shoots and chlorophyll content (% of control) in leaves after rice, corn ( Zea mays L. cv. Honey Bantam), E. oryzicola, E. crus-galli Beauv. var. crus-galli, and E. crus-galli var. formosensis Ohwi were treated with quinclorac. These results suggest that the difference in hereditary antioxidative ability is one factor that results in the particularly high selectivity of quinclorac between rice and E. oryzicola.

N-Butene Conversion on H-Ferrierite Studied by 13C MAS NMR

13C MAS NMR analysis of the hydrocarbon products formed from the selectively 13C-labeled n-but-1-ene on zeolite ferrierite (H-FER) in a closed batch reactor revealed the following successive steps of the olefin conversion with temperature increase from 300 to 823 K: a double-bond-shift reaction, scrambling of the selective 13C label in the formed n-but-2-ene, oligomerization (dimerization), conjunct polymerization, formation of condensed aromatics, and formation of the simple aromatics. Arguments in favor of either bimolecular or pseudo-monomolecular mechanisms are provided, excluding at the same time the monomolecular isomerization of n- to isobutene on a fresh sample. The arguments are based on selective label redistribution in the n-but-2-enes, the impossibility of the existence of isobutene inside the pores of the zeolite under static conditions and the observation of n-but-2-enes oligomerization (dimerization). Conjunct polymerization leads to the formation of alkyl-substituted cyclopentenyl cations (CPCs), which can serve as an intermediate for pseudo-monomolecular isomerization. Carbonaceous deposits (polycyclic aromatics), which deactivate the catalyst in the isomerization reaction, are formed from the CPCs. Polycyclic aromatics are transformed into simple aromatics with methane and ethane evolution at 823 K.

N-Butene Conversion on H-Ferrierite Studied by 13C MAS NMR

13C MAS NMR analysis of the hydrocarbon products formed from the selectively 13C-labeled n-but-1-ene on zeolite ferrierite (H-FER) in a closed batch reactor revealed the following successive steps of the olefin conversion with temperature increase from 300 to 823 K: a double-bond-shift reaction, scrambling of the selective 13C label in the formed n-but-2-ene, oligomerization (dimerization), conjunct polymerization, formation of condensed aromatics, and formation of the simple aromatics. Arguments in favor of either bimolecular or pseudo-monomolecular mechanisms are provided, excluding at the same time the monomolecular isomerization of n- to isobutene on a fresh sample. The arguments are based on selective label redistribution in the n-but-2-enes, the impossibility of the existence of isobutene inside the pores of the zeolite under static conditions and the observation of n-but-2-enes oligomerization (dimerization). Conjunct polymerization leads to the formation of alkyl-substituted cyclopentenyl cations (CPCs), which can serve as an intermediate for pseudo-monomolecular isomerization. Carbonaceous deposits (polycyclic aromatics), which deactivate the catalyst in the isomerization reaction, are formed from the CPCs. Polycyclic aromatics are transformed into simple aromatics with methane and ethane evolution at 823 K.

Protoporphyrinogen-IX Oxidase Inhibitors: Bioactivation of Thiadiazolidines

The bioactivation of thiadiazolidine-type peroxidizing compounds was examined with thiosemicarbazides as model intermediates. Peroxidizing activities of three sets of thiadiazolidines (5-arylimino-3,4-tetramethylene-1,3,4-thiadiazolidines), thiosemicarbazides (4-aryl-1-ethylthiocarbonyl-1,2-tetramethylenethiosemicarbazides), and triazolidines (4-aryl-1,2-tetramethylene-1,2,4-triazolidines) were assayed for protopor- phyrinogen-IX oxidase (Protox) inhibition with Protox isolated from corn etioplasts and for phytotoxic parameters of growth, chlorophyll content, and ethane evolution obtained with Scenedesmus acutus cells. Protox inhibitory activity of thiosemicarbazides was intermediate between that of thiadiazolidines and triazolidines. Phytotoxic parameters of thiosemicarbazides obtained from S. acutus cells were quite identical to those of triazolidines, although phytotoxic parameters of thiadiazolidines exhibited a slightly different pattern. Phytotoxic activities of 5-(4-bromophenyl)-3,4-tetramethylene-1,3,4-thiadiazolidin-2-one (thiadiazolidine 1 ) and 5-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3,4-tetramethylene-1,3,4-thiadiazolidin-2-one (thiadiazolidine 4 ) were similar to those of the corresponding triazolidines, but phytotoxicities exhibited by 5-(4-(4-chlorobenzyloxy)phenyl)-3,4-tetramethylene-1,3,4-thiadiazolidin-2-one (thiadiazolidine 7 ) were 10 times less active with S. acutus than those of the corresponding triazolidine. Three thiosemicarbazides exhibited rapid conversion into triazolidines both in buffer at pH 7 (ca. 25–50%, 5 min incubation) and in Scenedesmus cultures (ca. 75%, 5 h incubation). Thiadiazolidines 1 and 4 were converted into corresponding triazolidines (ca. 70%) in S. acutus but were converted in buffer only in the presence of glutathione S -transferase plus ethylmercaptan, although thiadiazolidine 7 was not converted in the Scnedesmus culture. Apparently, the conversion step from thiadiazolidine to the thiosemicarbazide intermediate is enzymatic and the thiosemicarbazide intermediate to triazolidine is a spontaneous, nonenzymatic step.

Involvement of Ethylene in the Induction of Cotton Defoliation by the Isoindoldione Cinidon-ethyl

The effect of the isoindoldione herbicide cinidon-ethyl on leaf abscission and the role of ethylene synthesis in the mechanism of action were studied in cotton (Gossypium hirsutum L. cv. Stoneville 825). Cinidonethyl is a new inhibitor of protoporphyrinogen IX oxidase in tetrapyrrole biosynthesis, which leads to the formation of 1-aminocyclopropane-1-carboxylic acid (ACC)-derived ethylene as a side effect (K. Grossmann and H. Schiffer, Pestic. Sci.55, 687 (1999)). Foliar application of cinidon-ethyl to young cotton plants at the fourth leaf stage resulted in a concentration-dependent increase in ethylene evolution and leaf abscission. Concomitantly, the fresh weight of abscised leaves was decreased. Within 2 days, cinidon-ethyl, strictly localized to blades of primary leaves of plants, induced maximum levels of ethylene, ACC, and conjugated ACC in the tissue. Ethane evolution as an indicator for membrane peroxidation remained unchanged within this period. Between the 2nd and 3rd days, a transient rise in ethylene and particularly ACC was observed in the petiole and abscission zone. Subsequently, leaf abscission was induced days after treatment. Radiotracer studies showed that cinidon-ethyl is effective through contact action. After leaf blade application of [14C]cinidon-ethyl, only trace amounts of 14C were translocated basipetally to the abscission zone. Therefore, it appears that ACC is transported as a signal from the leaf blade to the abscission zone, where metabolic conversion releases ethylene, which is implicated in leaf abscission. In accordance, cinidon-ethyl-induced defoliation was gradually reduced by increasing concentrations of aminoethoxyvinylglycine, an inhibitor of ethylene formation. The effect was completely restored by the addition of ACC.

Protoporphyrinogen oxidase-inhibiting activity of the new, wheat-selective isoindoldione herbicide, cinidon-ethyl

Cinidon-ethyl (BAS 615H) is a new herbicide of isoindoldione structure which selectively controls a wide spectrum of broadleaf weeds in cereals. The uptake, translocation, metabolism and mode of action of cinidon-ethyl were investigated in Galium aparine L, Solanum nigrum L and the tolerant crop species wheat (Triticum aestivum L). When plants at the second-leaf stage were foliarly treated with cinidon-ethyl equivalent to a field rate of 50 g ha−1 for 48 h, the light requirement for phytotoxicity and the symptoms of plant damage in the weed species, including rapid chlorophyll bleaching, desiccation and necrosis of the green tissues, were identical to those of inhibitors of porphyrin synthesis, such as acifluorfen-methyl. The selectivity of cinidon-ethyl between wheat and the weed species has been quantified as approximately 500-fold. Cinidon-ethyl strongly inhibited protoporphyrinogen oxidase (Protox) activity in vitro, with I50 values of approximately 1 nM for the enzyme isolated from the weed species and from wheat. However, subsequent effects of herbicide action, with accumulation of protoporphyrin IX, light-dependent formation of 1-aminocyclopropane-1-carboxylic acid-derived ethylene, ethane evolution and desiccation of the green tissue, were induced by cinidon-ethyl only in the weed species. After foliar application of [14C] cinidon-ethyl, the herbicide, due to its lipophilic nature, was rapidly adsorbed by the epicuticular wax layer of the leaf surface before it penetrated into the leaf tissue more slowly. No significant differences between foliar and root absorption and translocation of the herbicide by S nigrum, G aparine and wheat were found. After foliar or root application of [14C]- cinidon-ethyl, translocation of 14C into untreated plant parts was minimal, as demonstrated by combustion analysis and autoradiography. Metabolism of [14C]cinidon-ethyl via its E-isomer and acid to further metabolites was more rapid in wheat than in S nigrum and G aparine. After 32 h of foliar treatment with 50 g ha−1 of the [14C]-herbicide, approximately 47%, 36%, and 12% of the absorbed radioactivity, respectively, were found as unchanged parent or its biologically low active E-isomer and acid in the leaf tissue of G aparine, S nigrum and wheat. In conclusion, cinidon-ethyl is a Protox-inhibiting, peroxidizing herbicide which is effective through contact action in the green tissue of sensitive weed species. It is suggested that a more rapid metabolism, coupled with moderate leaf absorption, contribute to the tolerance of wheat to cinidon-ethyl. © 1999 Society of Chemical Industry

Desiccation stress in recalcitrantQuercus roburL. seeds results in lipid peroxidation and increased synthesis of jasmonates and abscisic acid

In a series of experiments the desiccation-sensitive seeds of Quercus robur were exposed to drying conditions both before and after a period of moist storage. Viability loss occurred at higher moisture contents in stored seed than in newly harvested seeds. Measurements were made at intervals during desiccation. In both stored and unstored seeds viability loss was preceded by an increase in the rate of ethane evolution, a commonly used indicator of lipid peroxidation, and by an increase in electrolyte leakage indicative of membrane damage. Jasmonic acid (JA), its methyl ester (MeJA) and ABA were quantified in the same extracts from both cotyledonary and axis tissues. The concentration of all three hormones was higher in the axis than in the cotyledons of untreated seeds and were within the range of concentrations quantified elsewhere in seed tissues from other species. The concentration of JA, MeJA and ABA progressively increased during drying in both cotyledons and axes of whole seeds and in excised axes prior to viability loss and then subsequently declined. The concentration of these hormones increased earlier during drying in stored seeds in line with their enhanced desiccation sensitivity. Exogenous JA, MeJA and ABA were shown to inhibit germination. However, none of these substances promoted ethylene evolution, which also inhibits germination of Q. robur seeds, or induced senescence-like deterioration. The results presented are discussed in relation to the nature of desiccation sensitivity and viability loss in Q. robur seeds.

Are ethane and pentane evolution and thiobarbituric acid reactivity specific for lipid peroxidation in erythrocyte membranes?

Peroxidation of human erythrocyte membranes was followed in vitro with head space analysis of ethane and pentane and a thiobarbituric acid assay in a standardized system liberating free oxygen radicals. Simultaneously, the decrease of the membrane palmitic, linoleic, arachidonic and docosahexaenoic acid was monitored. The recoveries of the peroxidation products of the red cell ghost preparations were compared with those obtained by peroxidation of pure fatty acids. Experiments using purified fatty acids revealed that ethane was preferentially produced from docosahexaenoic and linolenic, and pentane from linoleic and arachidonic acids. Thiobarbituric acid-reactive material (TBAR) was produced from each unsaturated fatty acid tested, but the amount was dependent on the number of carbon chain double bonds. During peroxidation of the erythrocyte ghosts, 72% of ethane and 51% pentane were produced during the first 12 h of incubation, whereas TBAR was produced at a constant rate throughout the 36-h test period. Hydrocarbon and TBAR production were similarly inhibited by desferoxamine (at p less than 0.005 and p less than 0.0001, respectively). The total recoveries of ethane, pentane and TBAR exceeded the amount expected by 7.8-, 1.4- and 5.5-fold, respectively. It was concluded that measurement of pentane is a reliable method to monitor lipid peroxidation during oxidative damage of the erythrocyte membrane.

Ethylene and ethane evolution during cold acclimation and deacclimation of ponderosa pine

Greenhouse container-grown ponderosa pine (Pinusponderosa var. scopulorum Engelm.) were cold acclimated and deacclimated in growth chambers during a 19-week regime. Seedling cold hardiness, bud dormancy, and ethylene and ethane evolution from excised needles were measured weekly. Ethylene and ethane evolution and the ethane/ethylene ratio declined from bud set to bud break and did not parallel changes in cold hardiness. Large standard errors of the ethylene evolution means made detecting statistical differences over time difficult. Significant deviations in the ethane evolution means were observed, however, and indicated a sharp decrease and recovery at the start of cold acclimation and a peak at the start of deacclimation. The ethane/ethylene ratio accentuated the declining trend from bud set to bud break and the two sharp deviations in the trend at the start of acclimation and deacclimation.

Inhibition of diquat-induced lipid peroxidation and toxicity in precision-cut rat liver slices by novel antioxidants

The ability of the novel antioxidants U-74,006F and U-78,517G and a known antioxidant ( N,N′-diphenyl- p-phenylenediamine, (DPPD)) to inhibit chemically induced (diquat dibromide) oxidative stress was examined in precision-cut liver slices. Previous studies in rat liver microsomes demonstrated the ability of these antioxidants to inhibit lipid peroxidation without preventing redox cycling of diquat. Diquat (1 m m) initiated lipid peroxidation in liver slices prepared from F344 rats. A 30-min preincubation with antioxidants inhibited formation of thiobarbituric acid reactive substances to control levels; ethane evolution, when elevated, was also inhibited by antioxidants. The toxicity of diquat (100 μ m-3 m m) was evaluated in liver slices; 1 and 3 m m diquat caused decreases in intracellular K + and intracellular LDH. Preincubation with antioxidants substantially decreased the toxicity of diquat as indicated by K + and LDH. Diquat significantly decreased total glutathione levels in the slices; the antioxidants did not significantly inhibit this diquat-dependent effect. In summary, diquat, a compound which undergoes redox cycling and produces oxidative stress, was shown to produce lipid peroxidation, glutathione depletion, and toxicity in liver slices. Two experimental antioxidants, a 21-aminosteroid (U-74,006F) and a trolox-amine (U-78,517G) as well as a known antioxidant (DPPD) were shown to be effective in preventing lipid peroxidation and reducing the subsequent toxicity.

Effects of novel antioxidants on carbon tetrachloride-induced lipid peroxidation and toxicity in precision-cut rat liver slices

Previous studies in rat liver microsomes have demonstrated the effectiveness of the 21-aminosteroid, U-74,006F, the troloxamine, U-78,517G, and N,N′-diphenyl- p-phenylenediamine (DPPD) in preventing carbon tetrachloride (CCl 4)-induced lipid peroxidation. Studies reported here utilized liver slices to assess whether these antioxidants could prevent lipid peroxidation and ensuing toxicity in a more complete/complex system. Liver slices prepared from Aroclor 1254-induced SD rats were incubated in Dulbecco's modified eagle media, 37°C, for up to 9 hr. Slices were preincubated with test compounds for 30 min prior to addition of CCl 4. Lipid peroxidation, as measured by the formation of thiobarbituric acid-reactive substances and ethane evolution, was decreased by U-74,006F (100 μ m), U-78,517G (100 μ m), and DPPD (1 μ m). CCl 4 (2.5 μl) decreased intracellular K + content, intracellular lactate dehydrogenase (LDH), and intracellular isocitrate dehydrogenase (ICD) activities over a 9-hr incubation period. Despite the marked effects on lipid peroxidation, U-74,006F showed no protection against K + or LDH loss and only moderate protection against ICD loss. U-78,517G showed no protection against K + loss but substantial protection against enzyme loss. DPPD demonstrated slight protection against K + and marked protection against enzyme loss. All three compounds inhibited CCl 4-induced lipid peroxidation; U-78,517G being most effective, followed by DPPD and U-74,006F. Inhibition of lipid peroxidation provided protection to the membrane structure as indicated by inhibition of LDH and ICD loss. The antioxidants failed to protect against CCl 4-induced toxicity (K + loss). These results suggest that CCl 4-induced lipid peroxidation and toxicity may be dissociable.

Early diagnosis of SO2-stress by volatile emissions in some crop plants.

Fumigation experiments with SO2 performed on the seedlings of three plant species viz, tomato (Lycopersicon esculentum), mung bean (Vigna radiata) and maize (Zea mays) resulted in the emission of volatiles. Acetaldehyde and ethanol were produced in the fumigated plants. In addition, there was also an increased production of ethylene and ethane. The production of these volatiles was positively correlated to the SO2 concentrations of 4.2 and 8.3 μmol m-3 (0.1 and 0.2 ppm). Ethylene was emitted primarily from SO2-stressed yet healthy leaves, whereas high ethane levels were detected in leaves with visible injury symptoms. However, with the appearance of visible injury symptoms, there was a decline in ethylene, acetaldehyde and ethanol emissions. Synthesis of ethylene and ethane seems to be a result of different metabolic pathways. Ethane evolution and its inhibition by antioxidants indicate SO2-mediated lipid peroxidation by free radical species formed during sulphite oxidation. Perturbation in the cellular respiratory machinery results in the formation of acetaldehyde and ethanol. Since the rates of emissions of ethane, acetaldehyde and ethanol fromplant species were positively correlated to their relative resistance to SO2, the production of these gases could be used as a reliable diagnostic tool for biomonitoring air pollution (SO2) stress.

EVIDENCE AND POSSIBLE MECHANISMS FOR MEMBRANE DETERIORATION DURING LONG-TERM STORAGE OF POTATO

Studies on the mechanisms by which growth potential of potato seed-tubers declines during aging suggest that membrane deterioration may be involved. Malondialdehyde (MDA) content, ethane evolution, solute leakage, and activity of the membrane-bound ethylene forming enzyme (EFE) were measured in tissues from 2, 14 and 26-month-old potato tubers as potential indicators of peroxidative damage and loss in membrane integrity. Solute leakage increased with tissue age, reflecting loss in membrane integrity. MDA content, a measure of lipid peroxidation, also increased with tuber age. Ethane is a product of free-radical-mediated peroxidation of polyunsaturated fatty acids (PUFA), and is therefore a sensitive marker of membrane damage. In the absence of fatty acid substrate, old tissue evolved less ethane than young tissue. However, addition of linoleate to the incubation medium stimulated more ethane from the oldest tissue, indicating a higher potential for ethane production. In vivo conversion of ACC to ethylene by EFE declined with age, possibly due to membrane deterioration. These studies show that peroxidation of PUFA may be influencing membrane integrity during long-term storage of potato.

Mechanism of herbicidal action and soybean selectivity of AKH-7088, a novel diphenyl ether herbicide

AKH-7088 {methyl (E,Z)-[[[1-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrophenyl]-2-methoxyethylidene]amino]acetate} is a highly selective herbicide for postemergence use in soybean culture. Both AKH-7088 and acifluorfen-methyl (AFM) [methyl 5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrobenzoate], which has been studied in detail as a representative diphenyl ether herbicide, exhibited the same light-requiring herbicidal activity, stimulated the ethane evolution in velvetleaf ( Abutilon theophrasti) leaf disks, as well as stimulated aminolevulinic acid (ALA) synthesis in cucumber leaves. As expected from the difference in soybean selectivity between AKH-7088 and AFM, both the ethane evolution activity and the stimulative effect of ALA synthesis of AKH-7088 in soybean ( Glycine max, cv, Williams) leaves were very weak compared to those of AFM. On the other hand, both compounds exhibited similar strong inhibition of growth in soybean-cultured cells. The absorption rate of [ 14C]AKH-7088 was three times faster in tolerant soybean leaves than in susceptible velvet leaves. A large amount of 14C was detected in the residue from the acetone extract of soybean leaves. After 6 hr, most of the 14C in the acetone extracts of soybean leaves was AKH-7088, whereas 56% of the 14C in the extracts from velvetleaf leaves was as metabolites. The metabolite extracted from velvetleaf leaves was almost all the free acid of AKH-7088 (I). The postemergence herbicidal activity of (I) in velvetleaf is much less than that of AKH-7088; however, the growth inhibition of (I) in tobacco cells was similar to that of AKH-7088. The mechanism of soybean selectivity of AKH-7088 is suggested that, compared to susceptible velvetleaf, tolerant soybean quickly absorbs AKH-7088 into the leaves and rapidly decomposes to inactive metabolites which cannot be extracted with acetone and does not keep the active metabolite (I) of AKH-7088 in the leaves.

Chilling Injury in Cucumbers (Cucumis sativa L.) Associated with Lipid Peroxidation as Measured by Ethane Evolution

ABSTRACTThe development of chilling injury in cucumbers stored at 4°C and 95% RH was evaluated. Irreversible damage due to chilling required 7 to 10 days as indicated by increases in tissue electrolyte leakage (from 30 to 70%), stress ethylene production (to 30‐60 pMol g_1 hr−1) and visual manifestations of injury. Low levels of ethane evolution (<1 pMol g−1 hr−1) were observed for unchilled and continuously chilled fruits. Upon rewarming, ethane evolution was stimulated by an order of magnitude following a prior chilling exposure of at least 7 days. These results indicate that the potentiation of lipid peroxidation in chilled cucumbers is associated with the onset of irreversible injury.

Chilling-Induced Lipid Degradation in Cucumber (Cucumis sativa L. cv Hybrid C) Fruit

Chilling at 4 degrees C in the dark induced lipid degradation in cucumber (Cucumis sativa L.) fruit upon rewarming at 14 degrees C. Rates of ethane evolution by fruits rewarmed after 3 days of chilling were up to four-fold higher than those evolved by unchilled (14 degrees C) fruits (0.02-0.05 picomoles gram fresh weight(-1) hour(-1)). This potentiation of lipid peroxidation occurred prior to irreversible injury (requiring 3 to 7 days of chilling) as indicated by increases in ethylene evolution and visual observations. Decreases in unsaturation of peel tissue glycolipids were observed in fruits rewarmed after 3 days of chilling, indicating the plastids to be the site of the early phases of chilling-induced peroxidation. Losses in unsaturation of tissue phospholipids were first observed only after chilling for 7 days. Phospholipase D activity appeared to be potentiated in fruits rewarmed after 7 days of chilling as indicated by a decrease in phosphatidylcholine (and secondarily phosphatidylethanolamine) with a corresponding increase in phosphatidic acid. These results indicate that lipid peroxidation may have a role in conferring chilling injury.