Ontogeny of monooxygenase activities in the marmoset monkey (Callithrix jacchus).

The pre- and postnatal development of monooxygenases in the liver and adrenal gland of marmoset monkeys (Callithrix jacchus) was investigated. Cytochrome P450 was detected in the fetal adrenal gland, but aldrin epoxidase, ethoxycoumarin O-deethylase, and ethoxyresorufin O-deethylase activities were below detection limits. Although fetal hepatic cytochrome P450 was not detected, low activities of aldrin epoxidase and ethoxycoumarin O-deethylase, but no ethoxyresorufin O-deethylase, could be detected in fetal liver. These enzymes attained adult marmosets activities when the offspring were approximately 2 months of age.     

棉铃虫的细胞色素P-450单加氧酶系与菊酯类杀虫剂抗药性的关系(英文)

细胞色素Ｐ－４５０单加氧酶系在昆虫抗药性中起重要作用。本文研究了棉铃虫抗性品系与敏感品系间细胞色素Ｐ４５０含量、对－硝基茴香醚Ｏ－脱甲基酶和艾氏剂环氧化酶的差异。结果表明：抗性品系中细胞色素Ｐ－４５０含量、对－硝基茴香醚Ｏ－脱甲基酶活性分别是敏感品系的１．７１倍和２．２１倍,而艾氏剂环氧化酶活性仅为１．３５倍。因此细胞色素Ｐ－４５０含量和对－硝基茴香醚Ｏ－脱甲基酶在棉铃虫抗菊酯品系中起重要作用。进一步讨论了不同抗性品系间抗性机制不同的原因。     

CYTOCHROME P450 MONOOXYGENASES ASSOCIATED WITH PYRETHROID RESISTANCE IN HELICOVERPA ARMIGERA (HÜBNER)

Abstract  The relationship between the cytochrome P-450 (cytP⁴⁵⁰ monooxygenase and insecticide resistance mechanisms in Helicoverpa armigera was studied. The level of cytP450 and activity of p -ni-troanisole ( p -NA) O-demethylase in resistant strain were 1. 71 times and 2. 21 times respectively higher as compared with those of the susceptible strain. Aldrin epoxidase activity showed 1. 35 fold strain difference. Therefore aldrin epoxidase might not be important for H. armigera resistance mechanism, the level of cytP450 and activity of p -NA O-demethylase might play a vital role in H. armigera resistance mechanisms. The reason of different resistance mechanisms among different H. armigera resistant strains is discussed.     

Biochemical characterization of hydrolytic and oxidative enzymes in insecticide resistant and susceptible strains of the German cockroach (Dictyoptera: Blattellidae).

We have identified resistance mechanisms in the German cockroach, Blattella germanica (L.), for propoxur and chlorpyrifos in strains of cockroaches that display multiresistance to several organophosphate and carbamate insecticides. The resistance mechanisms involve the combined effects of increased oxidative and hydrolytic metabolism and both strains are resistant to chlorpyrifos and propoxur. Experiments designed to test for similarity in metabolic enzymes suggest that, although the mechanisms involve similar processes, the enzymes responsible for insecticide detoxification are different in the two strains. Both resistant strains exhibited enhanced activity toward alpha-naphtholic esters relative to a standard susceptible strain; however, analysis of the progeny from resistant X susceptible crosses suggests that this general esterase activity is inherited differently than propoxur or chlorpyrifos resistance. Hybrids of the propoxur-resistant strain displayed the highest activity of all cockroaches tested, in contrast to hybrids of the chlorpyrifos-resistant strain, which were similar to the susceptible strain. Native gel electrophoresis of cytosolic preparations provided further evidence for differences in the pattern of hydrolytic enzymes and inheritance of resistance in the two strains. Analysis of components of the cytochrome P450-dependent monooxygenase system and activities toward model substrates indicate that the two resistance mechanisms also involve different oxidative processes. The propoxur-resistant strain displayed significantly higher levels of total cytochrome P450, but no other components were correlated with resistance. In contrast with the chlopyrifos-resistant strain, which was similar to the susceptible strain in all parameters measured, activity toward model substrates was higher in the propoxur-resistant strain than in any of the other strains and hybrids tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peroxide-supported in-vitro cytochrome P450 activities in Haemonchus contortus.

The potential for cytochrome P450 from Haemonchus contortus to operate in the oxygen-poor intestinal environment was investigated by examining the ability of the cytochrome to act in vitro as a peroxygenase in utilising cumene hydroperoxide for substrate oxidations not requiring molecular oxygen. Peroxygenase and NADPH-supported monooxygenase activities were measured in microsomes prepared from L3 and adult nematodes. Both cumene hydroperoxide- and NADPH-supported ethoxycoumarin O-deethylase and aldrin epoxidase activities were detected in larval microsomes. Adult microsomes showed low levels of cumene hydroperoxide-supported ethoxycoumarin O-deethylase, as well as NADPH- and cumene hydroperoxide-supported aldrin epoxidase activities. The use of inhibitors in ethoxycoumarin O-deethylase assays with larval microsomes indicated that the peroxygenase pathway does not proceed via ferrous cytochrome P450 (no inhibition by carbon monoxide), did not require molecular oxygen, and did not depend on electron flow from cytochrome P450 reductase. Larval activity was inhibited by typical cytochrome P450 inhibitors (piperonyl butoxide, SKF-525A, chloramphenicol, metyrapone, n-octylamine) and was unaffected by the peroxidase inhibitor salicylhydroxamic acid. In contrast, adult microsomal cumene hydroperoxide-supported ethoxycoumarin O-deethylase activity was significantly inhibited by both cytochrome P450 inhibitors and salicylhydroxamic acid. Adult microsomes also contained potassium ferrocyanide peroxidase activity utilising cumene hydroperoxide. This activity showed a similar pattern of inhibition by both cytochrome P450 and peroxidase inhibitors. Whilst the ability of larval H. contortus cytochrome P450 to act as a peroxygenase in vitro was demonstrated, the inhibition results with adult microsomes showing both cytochrome P450 and peroxidase activities require further investigation to clarify the nature of the adult microsomal cumene hydroperoxide-supported O-deethylase activity.     

微粒体多功能氧化酶系与棉铃虫对氰戊菊酯抗药性的关系

测定了棉铃虫Helicoverpa armigera抗氰戊菊酯种群及相对敏感种群不同组织微粒体的甲氧试卤灵-O-脱甲基酶、乙氧试卤灵-O-脱乙基酶、乙氧香豆素-O-脱乙基酶、芳烷基羟基化酶和艾氏剂环氧化酶的活性。结果表明：抗性种群棉铃虫中肠组织的这5种酶活性分别比敏感种群的活性提高了11.29、4.10、2.66、6.30和2.34倍,其脂肪体及体壁的相应酶活性则分别为敏感种群的1.46、6.80、1.36、4.05、1.48倍和12.32、2.2、1.33、0.80和0.51倍。两种群中,棉铃虫不同组织部位的各单加氧酶活性均不同,活性高低顺序在两种群间也不同。总体而言,均是中肠或脂肪体微粒体对不同底物的氧化代谢能力最强。     

Biochemical mechanisms of resistance in strains of Oryzaephilus surinamensis (Coleoptera: Silvanidae) resistant to malathion and chlorpyrifos-methyl.

The acetylcholinesterase, carboxylesterase, and cytochrome P450 monooxygenase activities of three strains of Oryzaephilus srinamensis (L.) were examined to better understand biochemical mechanisms of resistance. The three strains were VOS49 and VOSCM, selected for resistance to malathion and chlorpyrifos-methyl, respectively, and VOS48, a standard susceptible strain. Cross-resistance to malathion and chlorpyrifos-methyl was confirmed in VOS49 and VOSCM. Acetylcholinesterase activity was not correlated to resistance among these strains. VOS49 and VOSCM showed elevated levels of carboxylesterase activity based on p-nitrophenylacetate, alpha-naphthyl acetate, or beta-naphthyl acetate substrates. PAGE zymograms showed major differences in caboxylesterase isozyme banding among strains. VOSCM had one strongly staining isozyme band. A band having the same Rf-value was very faint in VOS48. The VOS49 carboxylesterase banding pattern was different from both VOSCM and VOS48. Cytochrome P450 monooxygenase activity was based on cytochrome P450 content, aldrin epoxidase activity, and oxidation of organophosphate insecticides, all elevated in resistant strains. The monooxygenase activity varied with insecticide substrate and resistant strain, suggesting specific cytochromes P450 may exist for different insecticides. The monooxygenase activity of the VOS49 strain was much higher with malathion than chlorpyrifos-methyl as substrates, whereas VOSCM monooxygenase activity was higher with malathion than chlorpyrifos-methyl as substrates. Results are discussed in the context of resistance mechanisms to organophosphate insecticides in O. surinamensis.     

The involvement of microsomal oxidases in pyrethroid resistance in Helicoverpa armigera from Asia

Five contemporary strains of the bollworm Helicoverpa armigera Hübner from China, Pakistan and India, all with high resistance to pyrethroids, were compared with a standard susceptible strain that originated from the Cote D'Ivoire in the 1970s ('SCD'). Two of the Chinese strains ('YGF' and 'YGFP') were derived by laboratory selection from a third, field collected strain ('YG'). The strain 'YG' exhibited 7-, 14- and 21-fold resistance to fenvalerate, cypermethrin and deltamethrin, respectively. After selection with fenvalerate for 14 generations ('YGF'), this increased to 1690-, 540- and 73-fold. Selection with a mixture of fenvalerate and piperonyl butoxide (PBO) for 14 generations ('YGFP') resulted in resistance ratios of 2510, 2920 and 286. The synergistic ratios to fenvalerate that resulted from pre-treatment of PBO were 5-, 462- and 12-fold in YG, YGF and YGFP strains, respectively. Resistance ratios for a Pakistani strain (PAK) were 2320-, 4100- and 223-fold to fenvalerate, cypermethrin and deltamethrin, respectively. The synergistic ratio of PBO to these pyrethroids was 450-, 950- and 11-fold. The strong synergism of pyrethroids by PBO implied that an oxidative metabolism could be involved in pyrethroid resistance in these resistant strains. The activities of cytochrome P450 monooxygenases from midguts of final instar larvae to p-nitroanisole (PNOD), ethoxycoumarin (ECOD), methoxyresorufin (MROD) significantly increased in all the resistant strains when compared with the susceptible strain. This further implies that cytochrome P450 monooxygenases are involved in pyrethroid resistance in Asian H. armigera. Comparative in vitro studies of the metabolism of 14C-deltamethrin by midgut microsomes of the resistant PAK and susceptible SCD strains showed that the resistant strain had a much greater capacity than the susceptible strain for the metabolic degradation of deltamethrin. This enhanced metabolic degradation occurred in the presence of NADPH which suggested an oxidative detoxification. In the resistant strains, minor increases in glutathione S-transferase activity (to the substrates CDNB and DCNB), and esterase activity (to the substrate alpha-naphthyl acetate) further suggested that, of the putative metabolic mechanisms, oxidases are the most important. This study provides the first evidence that cytochrome P450 monooxygenases are a major metabolic mechanism responsible for pyrethroid resistance in H. armigera from Asia.     

Aldrin Epoxidation in Flathead Mullet (Mugil cephalus): Possible Involvement of CYP1A and CYP3A

The primary objective of this study was to determine specific cytochrome P450 isozyme(s) involved in the metabolism of aldrin to its toxic metabolite dieldrin in flathead mullet (Mugil cephalus) liver microsomes. To identify the cytochrome P450 isozyme responsible for the aldrin metabolism in mullet liver, the effects of mammalian‐specific cytochrome P450 inhibitors and substrates were determined in the epoxidation reaction of aldrin. CYP3A‐related inhibitors, ketoconazole, SKF‐525A, and cimetidine, inhibited the metabolism of aldrin. The contribution of CYP1A to the aldrin metabolism was shown by the inhibition of 7‐ethoxyresorufin‐O‐deethylase activity in the presence of aldrin. The results indicate that CY1A and CYP3A are the cytochrome P450s involved in aldrin epoxidase activity in mullet. In addition, the suitability of aldrin epoxidase activity for monitoring of environmental pollution was also assessed in the fish samples caught from four different locations of the West Black Sea coast of Turkey.     

The larval feeding inhibition assay for the diagnosis of nematode anthelmintic resistance

A larval feeding assay for detection of nematode anthelmintic resistance to macrocyclic lactones and imidazothiazoles is described. The estimated concentration of anthelmintic required to inhibit larval feeding in 50% of L1's (IC50) that were resistant to either macrocyclic lactones or imidazothiazoles were significantly higher (P < or = 0.05) than those of susceptible isolates. Some variations in IC50 values were observed during the patent period of infection in all strains, although the pattern of the IC50 followed the same course. IC50 values varied in larvae developing from eggs shed throughout the patent period, with low values in the earliest larvae followed by higher values as the infection progressed, before decreasing at 70-90 days post-infection, although the low values of the first part of the patent period were not reached. However, the IC50 differences between all resistant and susceptible strains were significant throughout the whole patent period for ivermectin and levamisole. These results suggest that this technique may provide an alternative in vitro to detect anthelmintic resistance.     

Inheritance of diflubenzuron resistance and monooxygenase activities in a laboratory-selected strain of Lucilia cuprina (Diptera: Calliphoridae).

Inheritance of the high-level diflubenzuron resistance shown by a laboratory-selected strain of Lucilia cuprina (Wiedemann) was examined in matings with a susceptible reference strain. Progeny of reciprocal crosses between resistant females and susceptible males showed higher LC50 values than the alternate reciprocal cross, indicating some maternal influence on inheritance of resistance. Resistance was inherited in a codominant (S male x R female) or incompletely recessive (R male x S female) manner. Monooxygenase activities (aldrin epoxidation) of the F1 generations were also intermediate between the levels shown by the parental lines, however, inheritance of enzyme activities showed greater degrees of dominance than for resistance levels. There was also some maternal influence on inheritance of monooxygenase activities. Backcrosses of F1 generations to both susceptible and resistant parents did not fit the expected patterns for a major sex-linked resistance locus, indicating that the maternal influence on resistance inheritance was not associated with sex-linkage of a major resistance gene. The backcross data also failed to fit the model for a single major autosomal gene, suggesting that the resistance in the diflubenzuron-selected strain is polygenic, involving mechanisms additional to monooxygenases.     

Genetic analysis of aflatoxin B1 activation in rat hepatoma cells

Summary We present a strategy to elucidate the rate-limiting steps in activation of carcinogenic compounds by cytochromes P450. The principle was to select Reuber rat hepatoma cells for resistance to a procarcinogen. The hypothesis was that resistant cells should be systematically deficient in the P450 enzyme(s) involved in the activation process. Here we present an example of the use of this approach using aflatoxin B1 (AFB1), a potent hepatocarcinogen, as the selective agent. Parental cells as well as individual and pooled colonies selected for AFB1 resistance from three independent rat hepatoma lines were characterized for their content of 1) mRNA hybridizing to cDNA and/or oligonucleotide probes for cytochromes P450IIB1, P450IIB2 and albumin; and 2) aldrin epoxidase activity. Parental aflatoxin B1-sensitive cells were shown to express P450IIB1 but not P450IIB2. The majority of the aflatoxin B1-resistant clones failed to accumulate cytochrome P450IIB1 mRNA and expressed no or only very low aldrin epoxidase activity. Albumin mRNA levels remained unchanged, demonstrating that loss of expression of cytochrome P450IIB1 was not a consequence of a general dedifferentiation event. A revertant population showing restoration of both cytochrome P450IIB1 mRNA accumulation and aldrin epoxidase activity was fully sensitive to aflatoxin B1. The correlation between expression of cytochrome P450IIB1 and sensitivity to aflatoxin B1 in both parental cells and revertants strongly suggests that cytochrome P450IIB1 is a major contributor to the activation of aflatoxin B1 in rat hepatoma cells. The kind of strategy described here could be applied to other compounds that become cytotoxic for hepatoma cells following activation by cytochromes P450.Abbreviations AFB1 aflatoxin B1 - AE aldrin epoxidase - AHH aryl hydrocarbon hydroxylase - PAH polycyclic aromatic hydrocarbons - PB phenobarbital     

Detoxification of chlorotoluron in a chlorotoluron-resistant biotype of Alopecurus myosuroides. Comparison between cell cultures and whole plants

The metabolism of chlorotoluron in whole plants and cell suspensions was investigated in a previously characterized chlorotoluron-resistant biotype of Alopecurus myosuroides Huds. Both resistant plants and cell suspensions showed a greater capability to metabolize chlorotoluron to non-phytotoxic compounds than the respective susceptible counterparts. Data revealed that although both biotypes degraded chlorotoluron by N -dealkylation and ring-methyl hydroxylation, the resistant biotype showed an enhanced capacity to hydroxylate the parent herbicide. The cytochrome (Cyt) P450 inhibitor 1-aminobenzotriazole (ABT) inhibited the metabolism of chlorotoluron in both resistant and susceptible plants by reducing the formation of non-toxic aryl-hydroxylated derivatives and polar conjugates. N -demethylations were less susceptible to ABT than the other oxidative reactions, but this does not necessarily imply that the second detoxification activity is not Cyt P450, as some P450 activities are more susceptible to ABT than others. Ring-methyl hydroxylation inhibition affected the ability of resistant plants to recover photosynthetic activity after incubation in chlorotoluron, showing a similar fluorescence pattern to susceptible plants in the same conditions without ABT. Fluorescence and metabolism data strongly support the thesis of Cyt P450-mediated 4-methylphenyl hydroxylation as the main route of detoxification of chlorotoluron in the resistant biotype.     

Quantitative differences in aphid virulence and foliar symptom development on tomato plants carrying the Mi resistance gene

The Mi resistance gene in tomato reduces the feeding, fecundity, and survival of certain isolates of the potato aphid (Macrosiphum euphorbiae Thomas). This study compared the performance of two potato aphid isolates, WU11 and WU12, on nearly isogenic susceptible (Mi-) and resistant (Mi+) tomato cultivars. Although Mi significantly reduced the population growth of both aphids, WU12 numbers decreased by only 15% compared with 95% for isolate WU11. These results show that there are quantitative differences in virulence among potato aphid isolates. Compared with WU11 aphids, isolate WU12 caused more necrosis on both resistant and susceptible plants, and this increased damage may play a role in the partial virulence of isolate WU12. However, infestation with aphid isolate WU12 did not compromise plant defenses against isolate WU11 in resistant plants. Prior inoculation with either aphid isolate caused a modest reduction in the survival of WU12 adults, but this form of induced resistance was observed on both resistant and susceptible cultivars. Thus, Mi did not play a role in acquired resistance or mediate any indirect interactions between the two aphid isolates. Notably, the mode of action of Mi-mediated resistance seemed to differ depending on the aphid isolate tested. Mi dramatically deterred feeding by WU11 aphids, whereas the effects of resistance on isolate WU12 seemed to be caused primarily by antibiosis. Tolerance did not seem to be a major component of Mi-mediated responses, although resistant plants showed a modest reduction in the amount of foliar necrosis induced per aphid compared with susceptible plants.     

Relative contribution of detoxifying enzymes to pyrethroid resistance in a resistant strain of Helicoverpa armigera

Abstract:  The relative contribution of oxidases and esterases to pyrethroid resistance was studied in a YS-FP strain of Helicoverpa armigera from China. The YS-FP strain was derived from a field-collected strain (YS) by 16 generations of selection with a mixture of fenvalerate and phoxim. Compared with the YS strain, the YS-FP strain showed 1850- to >7140-fold resistance to four ester-bonded phenoxybenzyl alcohol pyrethroids (fenvalerate, deltamethrin, cypermethrin and cyhalothrin), >205-fold resistance to a non-ester phenoxybenzyl alcohol pyrethroid (etofenprox) and only 19-fold resistance to an ester-bonded methylated biphenyl alcohol pyrethroid (bifenthrin). The oxidase inhibitor piperonyl butoxide eliminated most the of resistance to fenvalerate, deltamethrin, cypermethrin, cyhalothrin and etofenprox, whereas the esterase inhibitor S,S,S -tributylphosphorothioate had a small synergistic effect for fenvalerate and cyhalothrin only. This suggests that the resistance to these pyrethroids in the YS-FP strain was mainly because of enhanced oxidative detoxification. The monooxygenase activities of the midguts of sixth-instar larvae of the YS-FP strain to substrates p -nitroanisole, ethoxycoumarin and methoxycoumarin were 3.7-, 4.7- and 10-fold, respectively, compared with that of the YS strain. Glutathione S -transferase activity and esterase activity were not significantly altered in the YS-FP strain. This confirms that enhanced oxidative detoxification was a major mechanism contributing to pyrethroid resistance in the YS-FP strain.     

Alteration of liver microsomal monooxygenases and substrate competition with aniline hydroxylase from rats chronically fed low-fat and high-fat-containing alcohol diets

Male Sprague-Dawley rats fed ethanol (EtOH) 36% of total calories for four weeks in a liquid diet containing either 34% (HF) or 12% (LF) of calories as fat were studied with respect to induction of microsomal monooxygenases (MFO) and substrate competition with EtOH-inducible aniline hydroxylase. The specific activity and turnover of aniline hydroxylase were induced to similar extents by HF-EtOH and LF-EtOH diets. Whereas, both LF-EtOH and HF-EtOH caused a decrease in the turnover of arylhydrocarbon (benzo[a]pyrene) hydroxylase (AHH) and aldrin epoxidase compared to pair-fed (PF) controls, LF-EtOH but not HF-EtOH increased the turnover of ethoxycoumarin and ethoxyresorufin O-deethylase (ECOD and EROD). The increase in ECOD and EROD and the decrease in AHH by EtOH is contrary to the parallel induction of these activities by J-methylcholanthrene (3-MC) and Aroclor 1254 (Aroclor). Benzo(a)pyrene (BaP) stimulated aniline hydroxylase in the HF-EtOH and PF systems, whereas with LF diet, stimulation was seen only in the EtOH group. Ethoxycoumarin (EC) inhibited aniline hydroxylase by microsomes from EtOH- and pyrazole-treated rats, whereas it stimulated aniline hydroxylase by control microsomes, suggesting that the EC effects were associated with EtOH-inducible cytochrome P-450. Ethoxyresorufin (ER) inhibited aniline hydroxylase in EtOH and PF groups, thus the differential effects of EC were not nonspecific O-deethylase effects. The effects of EtOH feeding on ECOD, EROD, and AHH (ie, substrates for 3-MC-inducible cytochrome P-450) displayed a greater differential between the experimental and control group with the LF- than with the HF-containing diet. The findings suggest that the alteration of certain MFO activities by chronic EtOH ingestion can be modified by the content of dietary fat. Moreover, the competition dynamics of MFO substrates toward EtOH-inducible aniline hydroxylase are altered by EtOH feeding and, in turn, modified by dietary fat.     

Toxicity and in vitro metabolism of t-permethrin in eastern subterranean termite (Isoptera: Rhinotermitidae)

Toxicity and metabolism of t-permethrin were evaluated in two colonies (UF and ARS) of the eastern subterranean termite, Reticulitermes flavipes (Kollar), collected in Gainesville, FL. The UF colony (LC50 = 1.86 micrograms per vial) was approximately twofold more tolerant of t-permethrin than the ARS colony (LC50 = 0.89 microgram per vial) at the LC50. The synergists piperonyl butoxide and S,S,S-tributylphosphorotrithioate increased t-permethrin toxicity four- and threefold (at the LC50) in the UF and ARS colonies, respectively. Despite these differences in t-permethrin susceptibility, microsomal oxidase activities toward surrogate substrate (aldrin epoxidase, and methoxyresorufin O-demethylase), cytochrome P450 content, and microsomal esterase activity toward alpha-naphthyl acetate did not differ significantly between the colonies. Moreover, no significant differences in qualitative and quantitative metabolism of [14C]t-permethrin were observed between the UF and ARS colonies for three enzyme sources (microsomal oxidase, microsomal esterase, and cytosolic esterase). Based on in vitro metabolism assays, the major detoxification route of t-permethrin in the UF and ARS termite colonies appears to be hydrolysis catalyzed by microsomal esterases.     

Effect of 28-homobrassinolide on susceptible and resistant cultivars of tomato after nematode inoculation

In vitro effects of 28-homobrassinolide (HBl) were evaluated on morphological and biochemical parameters of susceptible (Pusa Ruby) and resistant (PNR-7) cultivars of tomato, 5 days after nematode inoculation. In susceptible cultivar, nematode invasion reduced the plant growth while growth was enhanced after brassinosteroid treatment. In case of resistant plants, nematodes were not able to invade the roots and here also, pre-sowing treatment of seeds with HBl further enhanced the growth of plants. An increase in specific activities of antioxidative enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase, glutathione peroxidase and superoxide dismutase) was observed in susceptible plants treated with HBl. In resistant cultivar, nematode inoculation increased the specific activities which were further enhanced with HBl treatment. The results obtained in the present study indicated the ameliorative effects on tomato varieties treated with HBl even after nematode stress. Thus, suggesting a possible role of HBl in lessening the oxidative stress generated during nematode invasion and boosting the resistance capacity of plants.     

艾氏剂环氧化酶及细胞色素P－450对小菜蛾抗药性发展的影响

本文对室内长期饲养的小菜蛾（Ｐｌｕｔｅｌｌａ　ｘｙｌｏｓｔｅｌｌａ　Ｌ．）敏感品系和田间采集的抗性种群体内的艾氏剂平氧化酶及细胞色素Ｐ－４５０进行了比较研究。结果证明,艾氏剂环氧化酶在感性和抗性小菜蛾间存在着量及质的差异。抗性种群的艾氏剂环氧化酶的Ｖｍａｘ和Ｋｍ值分别为感性品系的５．４％和６．５倍。抗性种群的细胞色素Ｐ－４５０的含量是感性品系的１．１—１．３倍。艾氏剂环氧化酶在量上及质上的差异及细胞色素Ｐ－４５０含量的提高是导致小菜蛾抗药性发生与发展的重要机制之一。而且质的差异较之量的差异可能起着更为重要的作用．