Growth Analysis of Atrazine-Resistant and Atrazine-Sensitive Biotypes of Chenopodium album

Seed from atrazine-sensitive and atrazine-resistant biotypesof lambsquarters (Chenopodium album L.) was sown in pots containingquartz sand. Plants were grown under a controlled environmentin a growth room. On the 15th day after planting, four randomly-selectedplants of each biotype were harvested, and both fresh and dryweights of leaves, stems, roots and whole plants, together withleaf area, were determined for each plant. This was repeatedat 5-day intervals until the 60th day after sowing. Data from the resulting replicated 2 x 10 factorial configurationwere analysed using BMDP multiple regression programmes andorthogonal polynomials to produce best fit polynomial expressionsof time-to-harvest and biotype for the natural logarithm ofeach response. From these empirical models of plant growth,predictor functions for relative growth rates, leaf area andweight ratios, specific leaf area and unit leaf rate were generated. Examination of computer-generated plots of the various growthindices suggested that time-of-harvest was the most importantfactor in determining the magnitude of the responses. However,the two biotypes exhibited different growth patterns as indicatedby the presence of a significant biotype effect or biotype xtime interaction in all cases. The faster-maturing atrazine-sensitiveplants tended to have fairly dense leaves with relatively smallarea whereas the atrazine-resistant plants initially producedsmall root systems and relatively low density leaves. Moreover,the resistant biotype, despite being lighter at 2 weeks, weighedthe same as the sensitive plants by the 60th day due to a consistentlyhigher relative growth rate. The advantages of using balancedor orthogonal configurations together with multiple regressionprocedures to derive data-based empirical models of plant growthare discussed. Limitations to the routine use of empirical modelsare also considered. Chenopodium album L., lambsquarters, atrazine resistance, growth analysis, orthogonal polynomials, multiple regression analysis     

Variation of Transhexadecenoic Acid Content in Two Triazine Resistant Mutants of Chenopodium album and Their Susceptible Progenitor

Two atrazine resistant nutants of Chenopodium album L. and their susceptible progenitor were analyzed for lipid composition. In the phosphatidyldiacylglycerol the Δ3-trans-hexadecenoic acid (C16:1 trans) percentage was higher in the two resistant phenotypes. However, this difference appears later in the development of the leaves and is not clearly observed in young leaves and seedlings. Thus, the increase of the C16:1 trans during the leaf development of the resistant phenotypes is probably a secondary effect of the psbA mutation that arises in compensation for some photosynthesis deficiency. The significance of the lipid differences shown between the two resistant mutants is discussed in terms of whether they are responsible of the two different levels of herbicide resistance observed in the field.     

Reduction of Nitrite and Nitrate to Ammonium on Pyrite

An important constraint on the formation of the building blocks of life in the Hadean is the availability of small, activated compounds such as ammonia (NH(3)) relative to its inert dinitrogen source. Iron-sulfur particles and/or mineral surfaces have been implicated to provide the catalytic active sites for the reduction of dinitrogen. Here we provide a combined kinetic, spectroscopic, and computational modeling study for an alternative source of ammonia from water soluble nitrogen oxide ions. The adsorption of aqueous nitrite (NO (2) (-) ) and nitrate (NO (3) (-) ) on pyrite (FeS(2)) and subsequent reduction chemistry to ammonia was investigated at 22°C, 70°C, and 120°C. Batch geochemical and in situ Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR) spectroscopy experiments were used to determine the reduction kinetics to NH(3) and to elucidate the identity of the surface complexes, respectively, during the reaction chemistry of NO (2) (-) and NO (3) (-) . Density functional theory (DFT) calculations aided the interpretation of the vibrational data for a representative set of surface species. Under the experimental conditions used in this study, we detected the adsorption of nitric oxide (NO) intermediate on the pyrite surface. NH(3) production from NO (2) (-) occurred at 70 and 120°C and from NO (3) (-) occurred only at 120°C.     

Phenotypic plasticity to light competition and herbivory in Chenopodium album (Chenopodiaceae)

Competition and herbivory are ubiquitous environmental challenges that affect most plants. We examined the influence of phenotypic responses to either competition or herbivory on the subsequent response of the plants to the other factor. The stem-elongation response of Chenopodium album to light competition attenuated its resistance to caterpillar herbivory in terms of herbivore mortality, but not in terms of growth of the survivors. Plant responses to herbivory did not affect subsequent responses to light competition. Thus, plants were largely able to express phenotypic plasticity (a proportional increase in the phenotype) following previous exposure to a different environmental factor. Although plants were able to express sequential plasticity, the final phenotype expressed was limited by exposure to previous environmental factors: induced resistance reduced plant height and stem elongation made plants more palatable to herbivores. Phenotypic plasticity in response to competition and herbivory may thus limit the subsequent expression of adaptive phenotypes.     

Nitrate and Nitrite Reduction by Wolffia arrhiza

Nitrate reductase was not found to be present in or associated with partially purified, intact chloroplasts aqueously isolated from Wolffia arrhiza. Such chloroplasts are capable of using nitrite but not nitrate as an electron acceptor during light-stimulated electron transport in the absence of additional cytoplasmic components. When nitrite acts as an electron acceptor under these conditions, on the average 1.5 moles of oxygen are evolved per mole of nitrite reduced by the chloroplasts, indicating a probable reduction of nitrite to ammonia. Chloroplasts ruptured by osmotic shock fail to reduce nitrite in the absence of additional components.     

Aluminium Toxicity Modulates Nitrate to Ammonia Reduction

Two weeks-old maize (Zea mays cv. XL-72.3) plants were exposed to Al concentrations 0 (Al0), 9 (Al9), 27 (Al27) or 81 (Al81) g m-3 for 20 d in a growth medium with low ionic strength. Thereafter, the Al concentration-dependent interactions on root nitrate uptake, and its subsequent reduction to ammonia in the leaves were investigated. Al concentrations in the roots sharply increased with increasing Al concentrations while root elongation correspondingly decreased. Root fresh and dry masses, acidification capacity, and nitrate and nitrogen contents decreased from Al27 onwards, whereas leaf nitrogen, nitrate, nitrite, and ammonia concentrations decreased starting with Al9. Electrolytic conductance increased by 60 % in root tissues from Al0 to Al81 but it did not increase significantly in the leaves. In Al9, Al27, and Al81 plants a decrease in shoot fresh and dry masses was observed. Al concentrations between 0 and 27 g m-3 increased net photosynthetic rate, stomatal conductance, and the quantum yield of photosynthetic electron transport, whereas the intercellular CO2 concentration was minimum in Al27 plants. In the leaves, nitrate reductase (E.C. 1.6.6.1) activity increased until Al27, and nitrite reductase (E.C. 1.6.6.4) activity until Al81. Hence there may be an Al mediated extracellular and intracellular regulation of root net nitrate uptake. Nitrate accumulation in the roots affects the translocation rates and, therefore, the nitrate concentration in the leaves. The in vivo reducing power generated by the photosynthetic electron flow does not limit nitrate to ammonia reduction, and the increase of maximum nitrate and nitrite reductase activities parallels the decreasing nitrate, nitrite, and ammonia concentrations.     

Reduction of Nitrate and Nitrite by Subcellular Preparations of Anabaena cylindrica. I. Reduction of Nitrite to Ammonia

Reduction of nitrite by cell-free preparations of Anabaena cylindrica in the dark has been investigated. Nitrite-reducing activity was recovered in a supernatant fraction. The nitrite reductase system was partially purified by column chromatography on Sephadex G-75. NADPH could serve as an H-donor. NADH was completely inactive. The reduction required ferredoxin which mediated the transfer of electrons from NADPH to nitrite. Ferredoxin was successfully replaced with methyl viologen, benzyl viologen and diquat. The nitrite-reducing activity was inhibited by KCN, and by 2,4-dinitrophenol and arsenate at higher concentrations. The extent of nitrite reduction by NADPH was dependent on the oxidation-reduction states of NADP and ferredoxin.     

Dissimilatory Nitrate Reduction in Anaerobic Sediments Leading to River Nitrite Accumulation

Recent studies on Northern Ireland rivers have shown that summer nitrite (NO(inf2)(sup-)) concentrations greatly exceed the European Union guideline of 3 (mu)g of N liter(sup-1) for rivers supporting salmonid fisheries. In fast-flowing aerobic small streams, NO(inf2)(sup-) is thought to originate from nitrification, due to the retardation of Nitrobacter strains by the presence of free ammonia. Multiple regression analyses of NO(inf2)(sup-) concentrations against water quality variables of the six major rivers of the Lough Neagh catchment in Northern Ireland, however, suggested that the high NO(inf2)(sup-) concentrations found in the summer under warm, slow-flow conditions may result from the reduction of NO(inf3)(sup-). This hypothesis was supported by field observations of weekly changes in N species. Here, reduction of NO(inf3)(sup-) was observed to occur simultaneously with elevation of NO(inf2)(sup-) levels and subsequently NH(inf4)(sup+) levels, indicating that dissimilatory NO(inf3)(sup-) reduction to NH(inf4)(sup+) (DNRA) performed by fermentative bacteria (e.g., Aeromonas and Vibrio spp.) is responsible for NO(inf2)(sup-) accumulation in these large rivers. Mechanistic studies in which (sup15)N-labelled NO(inf3)(sup-) in sediment extracts was used provided further support for this hypothesis. Maximal concentrations of NO(inf2)(sup-) accumulation (up to 1.4 mg of N liter(sup-1)) were found in sediments deeper than 6 cm associated with a high concentration of metabolizable carbon and anaerobic conditions. The (sup15)N enrichment of the NO(inf2)(sup-) was comparable to that of the NO(inf3)(sup-) pool, indicating that the NO(inf2)(sup-) was predominantly NO(inf3)(sup-) derived. There is evidence which suggests that the high NO(inf2)(sup-) concentrations observed arose from the inhibition of the DNRA NO(inf2)(sup-) reductase system by NO(inf3)(sup-).     

Nitrate Reduction to Nitrite, a Possible Source of Nitrite for Growth of Nitrite-Oxidizing Bacteria

Growth yields and other parameters characterizing the kinetics of growth of nitrite-oxidizing bacteria are presented. These parameters were measured during laboratory enrichments of soil samples with added nitrite. They were then used to reanalyze data for nitrite oxidizer growth in a previously reported field study (M. G. Volz, L. W. Belser, M. S. Ardakani, and A. D. McLaren, J. Environ. Qual. 4:179-182, 1975), where nitrate, but not nitrite or ammonium, was added. In that report, analysis of the field data indicated that in unsaturated soils, the reduction of nitrate to nitrite may be a significant source of nitrite for the growth of nitrite oxidizers. A yield of 1.23 × 10⁴ cells per μg of N was determined to be most appropriate for application to the field. It was determined that if nitrite came only from mineralized organic nitrogen via ammonium oxidation, 35 to 90% of the organic nitrogen would have had to have been mineralized to produce the growth observed. However, it is estimated that only about 2% of the organic nitrogen could have been mineralized during the growth period. Thus, it appears that another source of nitrite is required, the most likely being the reduction of nitrate to nitrite coupled to the oxidation of organic matter.     

Seed Germination in Chenopodium album L: Relationships between Nitrate and the Effects of Plant Hormones

Effects of ethylene, gibberellins, and kinetin on the germination of two lots of Chenopodium album L. seeds, collected from the field in 1982 and 1983, were studied in relation to the availability of nitrate. The experiments were conducted in darkness and at temperatures ranging from 12 to 32°C. Ethylene induced over 75% germination in the 1983 seed but had little effect on the 1982 seed. Nitrate was only slightly promotive in either of the two seed lots. A combination of ethylene and nitrate, however, acted synergistically on 1982 seed, resulting in as much germination as that induced in 1983 seed by ethylene alone. In 1983 seed, a combination of ethylene and nitrate was only marginally more effective than ethylene. A similar relationship was observed in the effects of gibberellic acid₄₊₇ (GA₄₊₇) and nitrate on seeds from the two lots. The 1982 seed, which responded synergistically to combinations of nitrate with ethylene or GA₄₊₇ was found to contain an extremely low endogenous level of nitrate as compared to 1983 seed. Thus, high levels of either endogenous or applied nitrate appeared to enhance the germination response to ethylene or GA₄₊₇.

Kinetin had no effect on 1982 seed and only a small promotive effect on 1983 seed. There was no synergism between kinetin and nitrate in either of the seed lots.

     

Flavonoid evidence for allopolyploidy in the Chenopodium album aggregate (Amaranthaceae)

The flavonoid chemistry of 16 species of Chenopodium was investigated, with an emphasis on C. album and its relatives. The chief compounds seen were 3-O-glycosides of quercetin, kaempferol and isorhamnetin. The latter two classes show a mutually exclusive distribution among the diploid and all but one tetraploid species. C. polyspermum is unusual in possessing O-methylation at the 4-, 6- and 7-positions, and C. murale is the only taxon to have 7-O-glycosylation. Acylated glycosides are common. C. album and related hexaploid taxa display a single flavonoid profile, providing no support for the recognition of more than one species. The hexaploid flavonoid profile represents an almost perfect summation of those of the diploids, C. suecicum and C. ficifolium. This apparent additive inheritance supports the hypothesis that these species (or taxa very similar to them) are involved in the ancestry of C. album. Chromosome numbers are reported for 14 of the species.     

Growth and Photosynthetic Characteristics of Two Biotypes of the Weed Black-grass (Alopecurus myosuroides Huds.) Resistant and Susceptible to the Herbicide Chlorotoluron

Response of two biotypes of black-grass (Alopecurus myosuroidesHuds.) to the herbicide, chlorotoluron, was characterized inglasshouse and laboratory studies. ED₅₀values, defined as theamount (kg active ingredient ha^-1) of chlorotoluron requiredto reduce fresh mass by 50% under standard conditions, weredetermined for a resistant biotype (39.3 kg a.i. ha^-1) collectedfrom Peldon, Essex, UK and a susceptible biotype (0.93 kg a.i.ha^-1) obtained commercially, giving a resistance factor of 42.The resistance factor was calculated as the ratio of ED₅₀valuesand describes the increase in amount of herbicide needed toreduce fresh mass by 50% in the resistant, compared to the susceptible,biotype. Resistance was further characterized by measurementsof whole plant growth and photosynthesis. Relative growth rate,number of tillers, leaf area and mean fresh mass were the samein untreated plants of both biotypes, and rates of photosynthesisat both high and low photon flux were similar, with no differencein apparent quantum yield. Photosynthesis by whole plants wasstudied over a 24 h period following chlorotoluron treatment.Resistant plants showed no reduction in photosynthesis overthis period, whereas photosynthesis by susceptible plants ceased10 h after treatment and did not recover. Alopecurus myosuroides ; black-grass; herbicide resistance; chlorotoluron     

Comparative Induction of Nitrate and Nitrite Uptake and Reduction Systems by Ambient Nitrate and Nitrite in Intact Roots of Barley (Hordeum vulgare L.) Seedlings

The induction by ambient NO3- and NO2- of the NO3- and NO2- uptake and reduction systems in roots of 8-d-old intact barley (Hordeum vulgare L.) seedlings was studied. Seedlings were induced with concentrations of NaNO3 or NaNO2 ranging from 0.25 to 1000 [mu]M. Uptake was determined by measuring the depletion of either NO3- or NO2- from uptake solutions. Enzyme activities were assayed in vitro using cell-free extracts. Uptake and reduction systems for both NO3- and NO2- were induced by either ion. The Km values for NO3- and NO2- uptake induced by NO2- were similar to those for uptake induced by NO3-. Induction of both the uptake and reduction systems was detected well before any NO3- or NO2- was found in the roots. At lower substrate concentrations of both NO3- and NO2- (5-10 [mu]M), the durations of the lag periods preceding induction were similar. Induction of uptake, as a function of concentration, proceeded linearly and similarly for both ions up to about 10 [mu]M. Then, while induction by NO3- continued to increase more slowly, induction by NO2- sharply decreased between 10 and 1000 [mu]M, apparently due to NO2- toxicity. In contrast, induction of NO3- reductase (NR) and NO2- reductase (NiR) by NO2- did not decrease above 10 [mu]M but rather continued to increase up to a substrate concentration of 1000 [mu]M. NO3- was a more effective inducer of NR than was NO2-; however, both ions equally induced NiR. Cycloheximide inhibited the induction of both uptake systems as well as NR and NiR activities whether induced by NO3- or NO2-. The results indicate that in situ NO3- and NO2- induce both uptake and reduction systems, and the accumulation of the substrates per se is not obligatory.     

Isoproturon Resistance in Phalaris minor: Study of Physiobiochemical Parameters in Isoproturon Susceptible and Resistant Biotypes and Their Hybrids

An experiment was conducted to study physio-biochemical parameters to delineate the molecular basis of resistance against isoproturon in Phalaris minor. The reciprocal crosses of isoproturon resistant and susceptible biotypes of P. minor were made during the first year of an experiment and during the next year, these F₁ hybrids with their respective parents were evaluated for physio-biochemical and growth parameters after spraying the weed @ 0.0, 0.5, 1.0 and 1.5 kg ha^?1 with isoproturon at 22^nd and 30^th DAS. The F₁s showed heterosis and the order of resistance against isoproturon in the four biotypes was R×S > R > S×R > S. This indicated that the resistance against isoproturon in P. minor is predominantly governed by cytoplasmic inheritance, but the nuclear inheritance also has some contribution.     

藜对干旱胁迫的生理生化反应

干旱是植物最易遭受的胁迫之一,每年由于干旱胁迫给农业造成损失几乎相当于其他所有环境因子胁迫所造成的损失的总和。通过人工控制水分模拟干旱来研究生长期的藜对干旱胁迫的生理生化反应,以期望为干旱农业的高效生产提供理论依据。以盆栽的藜为材料,用控制浇水的方法分对照、轻度胁迫、中度胁迫、重度胁迫4个组,研究了不同程度干旱胁迫对藜叶片的水分状况、渗透调节物质、活性氧代谢以及内生保护系统的影响。结果表明:在干旱胁迫下,藜叶片相对含水量(RW C)、自由水含量(FW C)下降,束缚水含量(BW C)上升;可溶性糖、脯氨酸、K 、C a2 含量增加,表现出藜对适度干旱有一定的适应性。但重度干旱胁迫,O2.产生速率和丙二醛(M DA)含量显著提高,导致膜损伤,质膜透性上升;超氧化物歧化酶(SOD)、过氧化物酶(POD)活性先上升,后下降;抗坏血酸(A SA)含量降低。过分干旱胁迫对藜会造成一定伤害。     

Enzymatic Degradation of Chlorophyll in Chenopodium album

The breakdown of chlorophyll (Chi) in crude extracts of Chenopodiumalbum (white goose foot) in the dark was examined. Derivativesof pheophorbide were formed when Chi or chlorophyllide wasincubated with depigmented crude extracts. The formation ofpheophorbide was completely prevented by heat treatment of extracts,indicating that the reaction was enzymatic, and the presenceof a Mg-releasing enzyme, the so called Mg-dechelatase, waspostulated. This hypothesis was strongly supported by the observationthat the formation of pheophorbide was inhibited by 51% by 10mM MgCl₂. Analysis by high-performance thin-layer chromatography(HPTLC) and liquid chromatography (HPLC) showed that the appearanceof chlorophyllide , pheophorbide 13²-hydroxychlorophyllide and pyropheophorbide was accompanied by a concomitant decreasein levels of Chi The formation of 13²-hydroxychloro-phyllide was not clearly an enzymatic reaction and requires furtherexamination. It appears that Chl is degraded in a crude extractof C. album via the following enzymatically catalyzed reactions (Received September 10, 1990; Accepted November 15, 1990)