Modeling a submicrometer electrostatic motor.

Numerical models are developed for a recently proposed submicrometer device that uses the electric field energy of a biased parallel-plate semiconducting capacitor to propel a piston through the open capacitor gap. Through variation of design parameters or applied external bias, actuator forces on the order of hundreds of piconewtons are developed for device size scales ranging from 10(-7) m to 10(-4) m per side. A rotary configuration of the device is also presented.

Antifungal anthracycline antibiotics, spartanamicins A and B from Micromonospora spp.

Spartanamicins A and B, two antifungal antibiotics, were produced by a culture of Micromonospora spp. strain No. MSU-43097 (ATCC 53803), isolated from a potted soil containing asparagus (Asparagus officinalis L.) plants. The antibiotics were isolated from the mycelial cake using organic solvents. The structures of spartanamicins A and B were determined by spectral and chemical means. Spartanamicin B is more active as an antifungal compound than it's analogue, A. The minimum inhibitory concentration for spartanamicin B on Candida albicans and Aspergillus, Cladosporium, Cryptococcus, Rhodotorula and Staphylococcus spp. ranged from 0.2 to 1 microgram/ml. It was not active against Staphylococcus aureus, Escherichia coli and Citrobacter spp. but some strains of S. aureus were sensitive.

2,2'-oxo-1,1'-azobenzene: microbial transformation of rye (Secale cereale L.) allelochemical in field soils byAcinetobacter calcoaceticus: III.

Acinetobacter calcoaceticus, a gram-negative bacterium isolated from field soil, was found to be responsible for the biotransformation of 2(3H)-benzoxazolinone (BOA) to 2,2'-oxo-1,1'-azobenzene (AZOB). Experiments were conducted to evaluate the transformation of BOA to AZOB by this microbe in sterile and nonsterile soil. Transformation studies with soils inoculated withA. calcoaceticus indicated that the production of AZOB increased linearly with the concentration of BOA in sterile soil and showed a quadratic trend in nonsterile soils. This also indicated that all soil types studied for the transformation experiments might containA. calcoaceticus capable of the conversion of benzoxazolinones.

2,2'-OXO-1,1'-azobenzene: Selective toxicity of rye (Secale cereale L.) allelochemicals to weed and crop species: II.

Three allelochemicals from rye or its breakdown products were evaluated for activity on garden cress (Lepidum sativum L.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], cucumber (Cucumis sativus L.), and snap bean (Phaseolus vulgaris L.). 2,4-Dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA), 2(3H)-benzoxazolinone (BOA), and 2,2'-oxo-1,1'-azobenzene (AZOB) were all applied singly at 50, 100, and 200 ppm and in two- and three-way combinations each at 50 and 100 ppm. AZOB at 100 and 200 ppm produced 38-49% more inhibition than DIBOA, while combinations of BOA/ DIBOA, which contained AZOB at 100 ppm had 54-90% more inhibition when compared to DIBOA/BOA combinations. All combinations were slightly antagonistic to barnyardgrass, while several combinations caused a synergistic response to garden cress germination and growth. Cucumbers and snap beans exhibited both types of responses, depending on the allelochemical combination and application rate. The plant-produced benzoxazinones were more inhibitory to crops than weeds. Therefore, improved herbicidal selectivity would be expected if there were rapid transformation of the benzoxazinones to the microbially produced AZOB.

In vitro antibacterial activity of faeriefungin, a new broad-spectrum polyene macrolide antibiotic.

The in vitro activity of faeriefungin, a new pentaene macrolide lactone antibiotic produced by Streptomyces griseus var. autotrophicus, against 263 clinical bacterial isolates was examined. In contrast to the related fungicidal antibiotics nystatin and amphotericin B, which show no activity against bacteria, faeriefungin showed bactericidal activity against all species of gram-positive bacteria examined. MICs for these species ranged from 8 to 64 micrograms/ml, and the MIC for 90% of the isolates tested was 32 micrograms/ml. Isolates of some fastidious gram-negative species, including Neisseria gonorrhoeae, N. meningitidis, and Haemophilus influenzae, were slightly susceptible to faeriefungin, with MICs ranging from 16 to 128 micrograms/ml, but all members of the families Enterobacteriaceae and Pseudomonadaceae, with the exception of Pseudomonas cepacia, were completely resistant to faeriefungin at the concentrations tested. Faeriefungin is also active against fungi, nematodes, and mosquito larvae. The mode of action of faeriefungin against both bacteria and fungi is under investigation.

2,2'-OXO-1, 1 '-azobenzene A microbially transformed allelochemical from 2,3-Benzoxazolinone: I.

2,2'-Oxo-1,1 '-azobenzene (AZOB), a compound with strong herbicidal activity, was isolated and characterized from a soil supplemented with 2,3-benzoxazolinone (BOA). A parallel experiment with 6-methoxy-2,3-benzoxazolinone (MBOA) yielded AZOB as well as its mono-(MAZOB) and dimethoxy-(DIMAZOB) derivatives. These compounds were produced only in the presence of soil microorganisms, via possible intermediates, I and II, which may dimerize or react with the parent molecule to form the final products. In the case of MBOA, it was shown that demethoxylation precedes the oxidation step. Although BOA and 2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) were leached out of rye residues, there were no detectable amounts of the biotransformation products in the soil. When BOA was mixed with soil and rye residue, either under field conditions or in vitro, AZOB was detected. Levels of free BOA in the soil were greatly reduced by incubation with rye residue. AZOB was more toxic to curly cress (Lepidium sativum L.) and barnyardgrass (Echinochloa crusgatti L.) than either DIBOA or BOA.

Isolation and characterization of phytotoxic compounds from asparagus (Asparagus officinalis L.) roots.

Potential allelochemicals from aqueous extracts of dried asparagus (Asparagus officinalis L.) roots were isolated and characterized. Active fractions separated by HPLC included ferulic, isoferulic, malic, citric, and fumaric acids. Soxhlet extraction of the residues also produced phytotoxic caffeic acid. Although none of these compounds, when applied singly, was active enough to account for the phytotoxicity of asparagus extracts, their combined effect might be additive or synergistic. An extract from lyophilized fresh root tissues contained a fraction that was one order of magnitude more toxic than any compound obtained from the dried roots. The most active component was isolated by TLC and characterized by [(1)H]NMR as methylenedioxycinnamic acid (MDCA). This compound provided severe inhibition of curly cress (Lepidium sativum L.) root and shoot growth at concentrations of 25 ppm or above.

Faeriefungin: a new broad-spectrum antibiotic from Streptomyces griseus var. autotrophicus.

Faeriefungin, a polyol polyene macrolide lactone antibiotic, was isolated from the mycelium of Streptomyces griseus var. autotrophicus, MSU-32058/ATCC 53668, collected from the soil sample of a fairy ring in an old lawn in Lansing, Michigan. Faeriefungin has some properties similar to the previously reported polyene macrolides, mycoticin and flavofungin, but possesses different physiochemical and biological properties. Aspergillus, Fusarium, Microsporum, Trichophyton, and Alternaria spp. were completely inhibited by faeriefungin at 3.2 micrograms/ml, Candida spp. at 5.5 micrograms/ml, and Pythium, Phialophora, Leptosphaeria spp., and some selected Gram-negative penicillin-resistant strains of Neisseria gonorrhoeae at 16.0 micrograms/ml. At a concentration of 100 ppm, it caused 100% mortality of mosquito larvae (Aedes aegypti, Rockefeller strain) and free-living nematodes (Panagrellus redivivus). Unlike the related polyene macrolides, faeriefungin is crystalline and stable with broad-spectrum antimicrobial and insecticidal activity. Preliminary cytotoxicity studies with human erythrocytes and rat liver epithelial cells indicated that faeriefungin and amphotericin B have comparable toxicity. Solution nmr study has indicated that faeriefungin is a mixture of two compounds, faerifungins A [1] and B [2], and that they differ in the attachment of a H or an Me at C-33.

Isolation, characterization and activity of phytotoxic compounds from quackgrass [Agropyron repens (L.)Beauv].

Previous experiments showed that legumes grown in the presence of living or herbicidally treated quackgrass residues or extracts exhibited reduced seedling root and shoot growth and decreased nodulation and nitrogen fixation. Aqueous extracts of quackgrass shoots were most inhibitory to plant growth. Upon sequential partitioning of an aqueous extract of quackgrass shoots, the ether extract possessed the most activity and caused 50% reductions in radicle elongation of eight crop and weed species at concentrations of less than 240 µg/ml (small-seeded species) and 1000 µg/ml (large-seeded species). Snapbeans (Phaseolus vulgaris L. "Bush Blue Lake") grown aseptically in agar containing an ether extract at 100 and 200 µg/ml exhibited severe root browning, lack of root hair formation, and a two- to three-fold reduction in root and shoot dry weights. The ether extract of quackgrass shoots had no inhibitory effect on the growth of fourRhizobium species in Petri dishes or two species in broth culture. Inhibitors present in the ether extract may influence the legumeRhizobium symbiosis indirectly by reducing legume root growth and root hair formation. The ether extract of quackgrass shoots was separated using high-pressure liquid, thin-layer, and liquid column chromatography in an attempt to isolate and identify the inhibitors responsible for the inhibition of seedling growth. Two closely related flavonoid inhibitors were isolated from the ether extract. One was identified as 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (tricin). Both flavonoids caused 50% inhibition of radicle elongation in cress (Lepidium sativum L. "Burpee curly") seeds at concentrations of less than 125 µg/ml. Both flavonoids were found in ether extracts of quackgrass shoots and rhizomes, but the largest amounts of both compounds occurred in quackgrass shoots collected from the field.

Role of benzoxazinones in allelopathy by rye (Secale cereale L.).

Two phytotoxic compounds [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)] were previously isolated and identified in 35-day-old greenhouse-grown rye shoot tissue. Both compounds were also detected by TLC in greenhouse-grown root and fieldgrown shoot tissue. The concentration of DIBOA varied in the tissues, with the greatest quantity detected in greenhouse-grown shoots. DIBOA and BOA were compared with ß-phenyllactic acid (PLA) and ß-hydroxybutyric acid (HBA) for activity on seed germination and seedling growth and were consistently more toxic than either compound. Dicot species tested, including lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), and redroot pigweed (Amaranthus retroflexus L.), were 30% more sensitive than the monocots tested. Of the two benzoxazinone compounds, DIBOA was most toxic to seedling growth. DIBOA and BOA reduced chlorophyll production inChlamydomonas rheinhardtii Dangeard, by 50% at 7.5 × 10(-5) M and 1.0 × 10(-3) M, respectively. Both DIBOA and BOA inhibited emergence of barnyardgrass (Echinochloa crusgalli L. Beauv.), cress (Lepidium sativum L.), and lettuce when applied to soil, indicating their potential for allelopathic activity.

Herbicidal effects of geldanamycin and nigericin, antibiotics from Streptomyces hygroscopicus.

Geldanamycin (2) and nigericin (1) (primarily the Na+ salt) are responsible for the phytotoxicity of a Streptomyces hygroscopicus strain found to be highly active in our screens for producers of herbicidal antibiotics. After extraction from the cells, the compounds were purified with column and thin layer layer chromatography on silica gel, bioassayed for inhibition of garden cress (Lepidium sativum L.) radicle elongation, and identified with ms, ir, nmr, and co-chromatography with authentic standards. Both caused 50% reduction in garden cress radicle growth at concentrations of 1-2 ppm and nearly complete inhibitions at 3-4 ppm. Symptoms of toxicity differed markedly for the two compounds. Geldanamycin at high concentrations caused radicles to turn brown and disintegrate, whereas, nigericin did not cause visible necrosis. Geldanamycin is structurally similar to the herbimycins, which are also produced by S. hygroscopicus and have been reported to have herbicidal activity. The phytotoxicity of geldanamycin and nigericin has stimulated investigation of their potential for use as natural product herbicides.

Separating the competitive and allelopathic components of interference : Theoretical principles.

The terms "competition" and "allelopathy" should be used in ways consistent with some set of criteria, perhaps those proposed in this discussion. Proposed proof of competitive interference includes: (1) identification of the symptoms of interference; (2) demonstration that the presence of the agent is correlated with reduced utilization of resources by the suscept; (3) demonstration of which resource(s) depleted by the agent are limiting resources; and (4) simulation of that interference (in the absence of the agent) by reduction of the supply of resources to levels that occur during interference. Proposed proof of allelopathic interference includes: (1) identification of the symptoms of interference; (2) isolation, assay, characterization, and synthesis of the toxin; (3) simulation of the interference by supplying the toxin as it is supplied in nature; and (4) quantification of the release, movement, and uptake of the toxin. It would be desirable but not essential to show that the selectivity of the toxin to various species corresponds to the range of species affected by the allelopathic agent. We propose that fulfillment of the above criteria would constitute proof of competitive or allelopathic interference. According to these criteria, it is possible that neither competitive nor allelopathic interference has been unequivocally proven at the present time. These criteria are proposed as a basis for evaluation of experimental evidence and as an indicator of deficiencies in our technology.

Experimental methodologies to evaluate allelopathic plant interactions : TheAbutilon theophrasti-Glycine max model.

It is difficult to clearly and unambiguously demonstrate an allelopathic mechanism of plant interference. Several types of experimental methodologies such as the additive design, substitutive designs, and several types of plant yield-plant population functions are discussed in terms of their relative merits in terms of providing quantitative and qualitative information in the development of an empirical basis to describe a plant interaction. Additionally, several types of mathematical and graphical representations are presented using data from the velvetleaf (Abutilon theophrasti) and soybean (Glycine max) interaction. The design provides agronomically relevant information about crop yield losses but confounds the separate effects of population density and species proportion in mixtures. The replacement series design separates these two variables by maintaining a constant population of plants while varying the relative proportion of each species in mixtures. The replacement series diagram, relative yield, relative replacement rate, ratio diagram, a scaling test, and the regression of individual yield on the associate yield are discussed in terms of their utility in providing insights into a plant interaction. Individual plant yield-plant population functions such as the "Y-D" and "C-D" effects, the "3/2 power law of self-thinning," and the "Sakai" test provide a basis to compare plant yield per plant versus plant population responses. Several types of interactions are characterized with this methodology. None of these experimental designs will clearly demonstrate an allelopathic plant interaction alone, but they do provide high-inference experimental methodologies to develop an empirical foundation to describe accurately a plant interaction upon which more specific hypotheses can be developed.

Exploitation of allelopathy for weed control in annual and perennial cropping systems.

A variety of crops, cultivars, and accessions have been evaluated over the past six years for superior capability to suppress weed growth. The most successful of these approaches has been to grow cover crops of rye (Secale cereale), wheat (Triticum aestivum), sorghum (Sorghum bicolor), or barley (Hordeum vulgare) to a height of 40-50 cm, desiccate the crops by contact herbicides or freezing, and allow their residues to remain on the soil surface. Often, up to 95% control of important agroecosystem weed species was obtained for a 30- to 60-day period following desiccation of the cover crop. The plant residues on the soil surface exhibit numerous physical and chemical attributes that contribute to weed suppression. Physical aspects include shading and reduced soil temperatures which were similarly achieved using poplar (Populus) excelsior as a control mulch. Chemical aspects apparently include direct release of toxins, as well as production of phytotoxic microbial products. Numerous chemicals appear to work in concert or in an additive or synergistic manner to reduce weed germination and growth.

Rye residues contribute weed suppression in no-tillage cropping systems.

The use of allelopathic cover crops in reduced tillage cropping systems may provide an ecologically sound and environmentally safe management strategy for weed control. Growers often plant winter rye (Secale cereale L.) for increased soil organic matter and soil protection. Spring-planted living rye reduced weed biomass by 93% over plots without rye. Residues of fall-planted/spring-killed rye reduced total weed biomass over bare-ground controls. Rye residues also reduced total weed biomass by 63% when poplar excelsior was used as a control for the mulch effect, suggesting that allelopathy, in addition to the physical effects of the mulch, did contribute to weed control in these systems. In greenhouse studies, rye root leachates reduced tomato dry weight by 25-30%, which is additional evidence that rye is allelopathic to other plant species.

Allelopathic potential of sorghum (Sorghum bicolor) : Isolation of seed germination inhibitors.

The major inhibitory components obtained after fractionation of an aqueous extract of field-grown sorghum (Sorghumbicolorcv. Bird-a-boo) herbage were quantified in terms of biological potency by indexing three aspects of cumulative cress (Lepidium sativum cv. Curlycress) seed germination. The inhibitory potential expressed in the crude aqueous extract reflected a complex interaction of numerous individual components of diverse chemical compositions and potencies. Some of these inhibitory components included chemical classes not previously associated with herbage phytotoxicity.

Quantification of allelopathic potential of sorghum residues by novel indexing of richards' function fitted to cumulative cress seed germination curves.

The inhibitory activity of aqueous extracts of field-grown sorghum (Sorghum bicolor cv. Bird-a-boo) herbage and roots was quantitatively indexed by three aspects of cumulative cress (Lepidium sativum cv. Curlycress) seed germination: the germination onset; weighted mean rate; and final germination percentage. Extract potency was greatest for herbage collected four weeks after planting but declined sharply thereafter as the plants matured. About 91% of the inhibitory activity obtained from four-week-old herbage was in a low molecular weight fraction. Differential effects of herbage and root extracts on cress seed germination suggest that the nature and/or proportion of biologically active substances extractable from these plant parts is dissimilar.

Biological suppression of weeds: evidence for allelopathy in accessions of cucumber.

Cucumber (Cucumis sativus L.) accessions from 41 nations were grown with two indicator species in a search for superior competitors. Of the plant introductions tested, one inhibited indicator plant growth by 87 percent and 25 inhibited growth by 50 percent or more. The toxicity of leachates from pots containing inhibitory cucumbers to indicator plants germinated in separate containers suggested allelopathy. Incorporation of an allelopathic character into a crop cultivar could provide the plant with a means of gaining a competitive advantage over certain weeds.