Differential effect of ammonium on the induction of nitrate and nitrite reductase activities in roots of barley (Hordeum vulgare) seedlings

The effect of exogenous NH₄⁺ on the induction of nitrate reductase activity (NRA; EC 1.6.6.1) and nitrite reductase activity (NiRA; EC 1.7.7.1) in roots of 8-day-old intact barley (Hordeum vulgare L.) seedlings was studied. Enzyme activities were induced with 0.1, 1 or 10 mM NO₃⁺ in the presence of 0, 1 or 10 mM NH₄⁺, Exogenous NH₄⁺ partially inhibited the induction of NRA when roots were exposed to 0.1 mM, but not to 1 or 10 mM NO₃⁺, In contrast, the induction of NiRA was inhibited by NH₄⁺ at all NO₃⁺ levels. Maximum inhibition of the enzyme activities occurred at 1.0 mM NH₄⁺ Pre-treatment with NH₄⁺ had no effect on the subsequent induction of NRA in the absence of additional NH₄⁺ whereas the induction of NiRA in NH₄⁺-pretreated roots was inhibited in the absence of NH₄⁺ At 10 mM NO₃⁺ L-methionine sulfoximine stimulated the induction of NRA whether or not exogenous NH₄⁺ was present. In contrast, the induction of NiRA was inhibited by L-methionine sulfoximine irrespective of NH₄⁺ supply. During the postinduction phase, exogenous NH₄⁺ decreased NRA in roots supplied with 0.1 mM but not with 1mM NH₃⁺ whereas, NiRA was unaffected by NH₄⁺ at either substrate concentration. The results indicate that exogenous NH₄⁺ regulates the induction of NRA in roots by limiting the availability of NO₃⁺. Conversely, it has a direct effect, independent of the availability of NO₃⁺, on the induction of NiRA. The lack of an NH₄⁺ effect on NiRA during the postinduction phase is apparently due to a slower turnover rate of that enzyme.     

Is the effect of priming plants,and a functional JAR1, negligible on the foraging behaviour and development of a generalist lepidopteran,Helicoverpa armigera?

Theory and recent literature suggest strong effects of induced plant defences in some plant herbivore systems. Few have studied behavioural effects on intact plants. Differences in foraging behaviour as well as weight gain were determined for first instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on Arabidopsis thaliana (L.) Heynh. (Brassicaceae) mutant and wild type plants, non‐primed, or primed by herbivore feeding or methyl jasmonate. The differences in feeding were primarily in the length of feeding time as opposed to the area fed on, feeding location, or frequency. More larvae dispersed from plants after priming by mite feeding than dispersed after caterpillar feeding. Other behavioural activities such as resting were not significantly affected. Early instars gained less weight feeding on ein2 (ethylene insensitive) mutant, but there was no difference in weight gain between larvae feeding on induced and non‐induced plants of the same type. We concluded that there are fitness consequences for neonates of the generalist H. armigera after feeding on induced plant tissues in some cases, and that distinct changes in behaviour are recognisable both at the fine scale and at grosser levels (dispersal). However, these changes are more subtle than might be expected.     

月季愈伤组织的诱导及植株再生

以可在黑龙江地区露地越冬的5个现代月季（Rosa chinensis）品种为实验材料,分别以其无菌苗的叶片和茎段为外植体,研究了愈伤组织诱导及植株再生方法。实验结果表明：5个寒地月季品种的叶片和茎段均可诱导出愈伤组织,2,4-D诱导愈伤组织的效果较好,高浓度的细胞分裂素不适合用于月季叶片和茎段愈伤组织的诱导;TDZ在月季愈伤组织分化培养过程中具有重要作用,光照培养可促进月季愈伤组织的分化,愈伤组织的分化能力随着继代次数的增加呈下降趋势。该实验成功地从2004-8和2004-9（2个月季品种）愈伤组织中诱导出再生植株,其愈伤组织的分化率分别为45%和38%。     

Induction of hepatic drug metabolizing enzymes by DL-methionine in rats

A single intraperitoneal injection of DL-methionine (500 mg/kg body wt.) to adult male Wistar rats was shown to significantly induce all the components of the hepatic microsomal mixed function oxidase system such as NADPH cytochrome C reductase activity, cytochromes P-450 and b₅, as well as activities of drug metabolizing enzymes such as aminopyrine demethylase and uridine 5′ -diphosphate-glucuronosyltransferase. Combined administration of nicotinamide (250 mg/kg body wt.) and DL-methionine (500 mg/kg body wt.) was shown to bring about an additional increase (25-30%) in the activities of these enzymes as compared to their induction on independent administration of the two endobiotics. In rats bearing Yoshida sarcoma (ascites) tumour as well as in normal rats injected with serum from tumour bearing animals, the decreased activities of hepatic mixed function oxidases could be restored to their normal levels by administration of DL-methionine (500 mg/kg body wt.) to these rats. Whereas actinomycin D (1 mg/kg body wt.) had no effect on the increased incorporation of [¹⁴C] labelled leucine into microsomal proteins following administration of nicotinamide, the enhanced incorporation of the label following DL-methionine administration was completely inhibited by the same dose of actinomycin D. Administration of cycloheximide (0·5 mg/kg body wt.) to rats could completely inhibit the increased incorporation of [¹⁴C] leucine into hepatic microsomal proteins following independent administration of nicotinamide and DL-methionine. Similar inhibitory pattern with actinomycin D and cycloheximide was also demonstrated in case of induction of NADPH cytochromeC reductase activity by both these endobiotics.     

Metallothionein induction by nonsteroidal antiinflammatory drugs

In the present study we report on the effects of commonly used nonsteroidal antiinflammatory drugs on metallothionein (MT) and MT-I mRNA levels. A single dose of chloroquine (100 mg/kg), diclofenac (100 mg/kg), indomethacin (10 mg/kg), or piroxicam (100 mg/kg) was administered ip to C57B1 mice. After 18 h, MT levels were determined with a Cd-saturation radioassay. MT-I mRNA levels were measured by Northern Blot analyses using a probe containing the mouse MT-I gene. All drugs tested caused an increase in the MT content of the liver but not of the kidneys and lung. The lowest and highest effects were observed with chloroquine (8 times the control value) and diclofenac (18 times), respectively. In accordance with the stimulation of MT synthesis, increased accumulation of hepatic MT-I mRNA could be demonstrated. These results indicate that elevated MT levels may contribute to the effectiveness of nonsteroidal antiinflammatory drugs in the treatment of rheumatoid arthritis (RA).     

药用植物肿节枫诱导前噬菌体有效组分的分析

在11种溶原性细菌系统中,以双层琼脂平板-纸片法检测药用植物肿节枫对前噬菌体的诱导作用,表明温和性噬菌体φ52 Ⅰ溶原化的金黄色葡萄球菌2009,对肿节枫的诱导反应最为敏感。其它溶原性菌株,包括曾用以筛选抗肿瘤药物的大肠杆菌K_(12)(λ)-K_(12)S系统都呈阴性反应。化学成分的进一步分析说明,仅肿节枫黄酮糖苷组分Ⅰ具有诱导活性。并与丝裂霉素C作了比较。     

Dependence of fluorescence behaviour and other photosystem-II characteristics on the nature of the nitrogen source for the filamentous cyanobacterium Oscillatoria chalybea

The filamentous cyanobacterium Oscillatoria chalybea grows phototrophically on a mineral medium in the presence of either nitrate or ammonium ions as nitrogen source at similar growth rates. In the absence of any combined nitrogen source in the medium the cyanobacterium also grows, although at a reduced growth rate. The steady state rate of oxygen evolution by filaments from these three culture conditions is approximately constant if compared on an equal chlorophyll basis. Qualitative differences, however, emerge, if transient phenomena, e.g. the oxygen gush, are investigated. Only nitrate-and nitrogen-free-grown cultures show an oxygen gush, whereas ammonium sulfate-grown cultures do not show this phenomenon. Fluorescence induction in O. chalybea shows a fast monophasic rise, comparable to the fluorescence rise curves of higher plant chloroplasts in the presence of dithionite. The steady state level of fluorescence in ammonium sulfate-grown cells is up to seven times higher than in nitrate-grown cells when compared on an equal chlorophyll basis. In ammonium sulfate-grown cells, DCMU (N,N-3,4-Dichlorophenyl dimethylurea) causes a further increase in fluorescence level. In nitrate-grown cyanobacteria, however, the effect of DCMU consists of a decrease of the steady state level of fluorescence. In context with earlier research on Anabaena cylindrica, another filamentous cyanobacterium, it appears that the type of the nitrogen source used for growth determines the main location of the DCMU-block in this organism. It thus appears that in O. chalybea the site of DCMU inhibition lies on the oxygen-evolving side of photosystem II, if the organism is grown on nitrate. If grown on ammonium sulfate, no substantial difference of the location of the inhibition site when compared to algae or higher plant chloroplasts is found.Thylakoid preparations of O. chalybea perform the usual Hill reactions with ferricyanide, p-benzoquinone or silicomolybdate as electron acceptors. In each case it is seen that with thylakoids of nitrate-grown cells the steady-state level of fluorescence is lowered by DCMU in the presence of these acceptors, which should be the case, if DCMU inhibits electron transfer on the donor side of photosystem II. According to the literature silicomolybdate accepts electrons mainly before the DCMU-block in higher plant chloroplasts. Hence, in higher plants this reaction is mainly DCMU-insensitive. In thylakoids of O. chalybea, however, the Hill reaction with silicomolybdate is DCMU-sensitive which provides further evidence that the DCMU-block is on the oxygen-evolving side of photosystem II in O. chalybea provided the cells have been grown on nitrate.Abbreviations DCMU N-N-3,4-Dichlorophenyl dimethylurea     

The Accumulation of Proteins with Chitinase Activity in the Culture Liquids of the Parent and Mutant Serratia marcescens Strains Grown in the Presence of Mitomycin C

The study of the accumulation pattern of extracellular proteins with chitinase activity in the parent Serratia marcescens strain Bú 211 (ATCC 9986) grown in the presence of mitomycin C and its mutant strain with the constitutive synthesis of chitinases grown in the absence of the inducer showed that chitinase activity appeared in the culture liquids of both strains at the end of the exponential phase (4 h of growth) and reached a maximum in the stationary phase (18–20 h of growth). The analysis of the culture liquids (12 h of growth) by denaturing electrophoresis in PAAG followed by the protein renaturation step revealed the presence of four extracellular proteins with chitinase activity and molecular masses of 21, 38, 52, and 58 kDa.