Inhibition of Respiration of Yeast by Photosynthesis Inhibiting Herbicides

In order to elucidate the mode of action of some herbicides, effect of several anilide type herbicides on the respiration of yeast cells was studied. The results obtained were as follows: 1) DCPA (3,4-dichloropropionanilide) and DCMU (3-(3,4-dichlorophenyl)-1,1- dimethylurea), the powerful inhibitors of the Hill reaction in photosynthesis, inhibited the oxygen uptake of yeast cells at low concentrations. 2) DCPA and DCMU inhibited the enzymic reduction of cytochrome-c by the yeast cell-free preparation, but not the reduction of dye. 3) The oxidation of cytochrome-b was inhibited in the yeast cells treated with DCPA or DCMU.     

Rapid Inhibition of Leaf Growth by Root Cooling in Wheat: Kinetics and Mechanism

Cooling of the roots was shown here to cause marked and rapidinhibition of leaf growth in wheat seedlings, as in some otherspecies. The root-shoot signal involved in this response wasinvestigated. Displacement transducers were used for the simultaneousmonitoring of leaf growth rate and leaf thickness in individualseedlings. Leaf water status was inferred from leaf thickness.Kinetics of changing water status were compared with those ofchanging leaf growth rate in the same seedling. Leaf water statuswas found to decline markedly beginning immediately after rootcooling. This occurs because cooling reduces the hydraulic conductivityof roots almost to zero. Apparent leaf growth rate was extremelysensitive to small changes in leaf water status, and the initialdecrease in leaf water status after root cooling was sufficientto cause cessation of leaf growth. Complications arising fromleaf elasticity and other sources were considered. Prolongedroot cooling caused a sustained depression in both leaf waterstatus and leaf growth rate. The effects of root cooling onleaf thickness and growth rate were completely prevented ifwater was made freely available to the shoot. It is thereforeconcluded that hydraulic factors (signals) can explain the short-and(at least in part) the medium-term effects of root cooling onleaf growth rate in wheat. Key words: Triticum durum L., leaf growth rate, hydraulic signals, root cooling     

Promotion of Sorghum Callus Growth by the s-Triazine Herbicides

Growth-promoting action of simazine and other s-triazine herbicides was detected by the use of sorghum (Sorghum bicolor [L]. Moench) callus tissue and the chlorophyll retention test. Soil application of simazine [2-chloro-4, 6-bis(ethylamino)-s-triazine] at sublethal levels nearly doubled the growth-promoting action of sorghum root exudates. Treated plants yielded up to 26% more total protein than untreated plants. This indicated that the level of callus growth-promoting action in the root exudate of the plant has a positive effect on its final total protein yield and confirms a positive effect of simazine on total protein content in certain instances. The results may provide a new understanding of the mode of action of s-triazines applied at sublethal levels in increasing protein content and certain enzymic activities of treated plants. It is speculated that the growth-promoting action of these herbicides is hormonal in nature and most likely kinetin-like.     

Inhibition of Yeast Growth by Methionine

The accumulation of S-adenosylmethionine in adenine-requiring yeast cells grown in a culture medium containing dl-, l-, or d-methionine was much larger than that in cells grown in a methionine-free medium. The accumulation of S-adenosyl-d-methionine in the cells was significantly lower than that of S-adenosyl-l-methionine. When yeast cells containing a large amount of S-adenosyl-l-methionine were incubated in an adenine-free medium, adenosylmethionine was degraded, but poor and insignificant growth was observed indicating the meager nature of this compound as an adenine source. No degradation of accumulated S-adenosyl-d-methionine was detected. Isotopic experiment revealed that S-adenosyl-l-methionine in the yeast cells turned over at a considerable rate when the medium contained both adenine and l-methionine. Most of the l-methionine assimilated appears to be metabolized via S-adenosyl-l-methionine.     

Studies on Herbicides and Plant Growth Regulators

With the aim of obtaining plant growth regulators, we have synthesized 1-aryloxyacylbenzimidazoles, 1-aryloxyacylindazoles, 2-aryloxyacyl-4,5,6,7-tetrahydroindazoles and 1-aryloxyacylbenzotriazoles by the acylation of azoles, and 1-aryloxyacyl-4,5,6,7-tetrahydroindazoles by the reaction of aryloxyacylhydrazines with 2-(hydroxymethylene)cyclohexanone. The structures of these compounds are discussed on the basis of nuclear magnetic resonance data.     

Effect of Selected Herbicides on Bacterial Growth Rates

Specific growth rate constants were used to evaluate the effects of selected herbicides on Erwinia carotovora, Pseudomonas fluorescens, and Bacillus sp. Comparison of growth rate constants permitted the identification of either stimulatory or inhibitory effects of these substances. E. carotovora was inhibited by 6,7-dihydrodipyrido(1,2-a:2'-c)pyrazinediium (diquat) and 4-hydroxy-3,5-diiodobenzonitrile (ioxynil) at 25 mug/ml; 1,1'-dimethyl-4,4'-bipyridinium (paraquat) at 50 mug/ml; and pentachlorophenol (PCP) at 10 mug/ml. P. fluorescens was inhibited by paraquat and PCP at 25 mug/ml and by 4-amino-3,5,6-trichloropicolinic acid (picloram) at 50 mug/ml. Stimulation of P. fluorescens was observed with 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) at 25 mug/ml. The Bacillus species was inhibited by diquat (25 mug/ml), ioxynil (10 mug/ml), and paraquat and PCP (5 mug/ml). No significant effect of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), or 1,1-dimethyl-3-(alpha,alpha,alpha-trifluoro-m-tolyl)urea (fluometuron) on growth rates of the bacteria was observed at 25 and 50 mug/ml.     

Growth Inhibition of Staphylococci by Sodium Thiosulphate

The addition of sodium thiosulphate to a medium as neutralizer of an iodine antiseptic resulted in unexpected growth inhibition of various strains of staphylococci and micrococci. The minimum growth inhibiting concentration varied with different strains. The inhibitory effect of sodium thiosulphate was more pronounced in media with low pH values than in those with high pH values, and was diminished by the addition of Tween 80. The action was also found to depend on the concentration of l -cystine in the medium. It is suggested that the use of sodium thiosulphate be avoided in growth media designed to neutralize iodine in disinfection efficiency tests when staphylococci or micrococci are used as test organisms.     

Kinetics of Denitrifying Growth by Fast-Growing Cowpea Rhizobia

Two fast-growing strains of cowpea rhizobia (A26 and A28) were found to grow anaerobically at the expense of NO₃⁻, NO₂⁻, and N₂O as terminal electron acceptors. The two major differences between aerobic and denitrifying growth were lower yield coefficients (Y) and higher saturation constants (K_s) with nitrogenous oxides as electron acceptors. When grown aerobically, A26 and A28 adhered to Monod kinetics, respectively, as follows: K_s, 3.4 and 3.8 μM; Y, 16.0 and 14.0 g · cells eq⁻¹; μ_max, 0.41 and 0.33 h⁻¹. Yield coefficients for denitrifying growth ranged from 40 to 70% of those for aerobic growth. Only A26 adhered to Monod kinetics with respect to growth on all three nitrogenous oxides. The apparent K_s values were 41, 270, and 460 μM for nitrous oxide, nitrate, and nitrite, respectively; the K_s for A28 grown on nitrate was 250 μM. The results are kinetically and thermodynamically consistent in explaining why O₂ is the preferred electron acceptor. Although no definitive conclusions could be drawn regarding preferential utilization of nitrogenous oxides, nitrite was inhibitory to both strains and effected slower growth. However, growth rates were identical (μ_max, 0.41 h⁻¹) when A26 was grown with either O₂ or NO₃⁻ as an electron acceptor and were only slightly reduced when A28 was grown with NO₃⁻ (0.25 h⁻¹) as opposed to O₂ (0.33 h⁻¹).     

Substrate Binding Sites of Leuconostoc Dextransucrase Evaluated by Inhibition Kinetics

Graphical analysis of inhibition kinetics for dextransucrase from Leuconostoc mesenteroides was done with typical inhibitors, competitive and noncompetitive. Based on the plots of Yonetani-Theorell and Semenza-Balthazar, mutual competition between the pairs of inhibitors of identical kinetic type was observed, while combination of competitive and noncompetitive inhibitors gave no significant mutual interactions. By the procedure of Nitta et al., binding sites for competitive and noncompetitive inhibitors were shown to be distant from each other. Moreover, two noncompetitive inhibitors competed with each other for a single binding site on the enzyme. Although biphasic reciprocal plots may suggest rather complicated binding of various inhibitors, the results obtained by the three graphical methods are fully explained when competitive and noncompetitive inhibitors for substrate sucrose bind to the so-called donor- and acceptor-sites of dextransucrase, respectively.     

Inhibition Kinetics of Sheep Brain Glutathione Reductase by Cadmium Ion

Glutathione reductase participates in preventing lipid peroxidation by oxygen radicals which results in cellular damage. The brain is among the organs most susceptible to cadmium-induced lipid peroxidation. The mechanism of free radical generation by Cd²⁺ is not well understood, but it is known that Cd²⁺ is an inhibitor of glutathione reductase. In this study, inhibition kinetics of the brain glutathione reductase by Cd²⁺ was investigated. Sheep brain enzyme (11,000-fold purified) was used for this purpose. The data were analyzed by a nonlinear curve fitting program. It was found that the inhibition was competitive with respect to oxidized glutathione and uncompetitive with respect to NADPH. Inhibition constants were found as 12.3 and 9.4 μM, respectively. These findings might contribute to the understanding of the mechanism of lipid peroxidation by Cd²⁺ in brain.     

Growth Inhibition by Phenylalanine in Euglena gracilis

The hydrolysis and esterification by a thermostable lipase from Humicola lanuginosa No. 3 were investigated. Both reactions occurred readily at temperatures between 45~50°C. Esterification by the enzyme with glycerol was observed to be specific towards fatty acids with carbon numbers of C12~C18. Laurie acid esters with different alcohols such as primary alcohols, terpene alcohols, eie., were also synthesized readily. Esterification by the enzyme was adversely affected by the water content (optimum, ca. 7%), however, the hydrolysis rate increased rapidly with increasing water content (optimum, az. 60%). The enzyme showed increased activity in organic solvent-aqueous reaction systems. Nevertheless, hydrolysis in complete organic phase reactions was found not to be feasible. Hydrolysis at a higher temperature (50 or 55°C) in a solvent free phase was almost the same as that in organic solvent-aqueous phase reactions. The components of glycerides varied considerably during hydrolysis, whereby esterification resulted in a higher quantity of mono- and diglycerides (about 40%), compared to in the case of hydrolysis, for which the value was about 10~20%.     

Energetics of Streptococcal Growth Inhibition by Hydrostatic Pressure

Growth of Streptococcus faecalis in complex media with various fuel sources appeared to be limited by the rate of supply of adenosine-5′ -triphosphate (ATP) at 1 atm and also under 408 atm of hydrostatic pressure. Growth under pressure was energetically inefficient, as indicated by an average cell yield for exponentially growing cultures of only 10.7 g (dry weight) per mol of ATP produced compared with a 1-atm value of 15.6. Use of ATP for pressure-volume work or for turnover of protein, peptidoglycan, or stable ribonucleic acid (RNA) did not appear to be significant causes of growth inefficiency under pressure. In addition, there did not seem to be an increased ATP requirement for ion uptake because cells growing at 408 atm had significantly lower internal K⁺ levels than did those growing at 1 atm. Pressure did stimulate the membrane adenosine triphosphatase (ATPase) or S. faecalis at ATP concentrations greater than 0.5 mM. Intracellular ATP levels were found to vary during the culture cycle from about 2.5 μmol/ml of cytoplasmic water for lag-phase or stationary-phase cells to maxima for exponentially growing cells of about 7.5 μmol/ml at 1 atm and 5.5 μmol/ml at 408 atm. N,N′-dicyclohexylcarbodiimide at a 10 μM concentration improved growth efficiency under pressure, as did Mg²⁺ or Ca²⁺ ions at 50 mM concentration. These agents also enhanced ATP pooling, and it seemed that at least part of the growth inefficiency under pressure was due to increased ATPase activity. In all, it appeared that S. faecalis growing under pressure has somewhat reduced ATP supply but significantly increased demand and that the inhibitory effects of pressure can be interpreted largely in terms of ATP supply and demand.     

The Inhibition of Seedling Growth by Streptomycin Sulfate

The action of streptomycin sulfate (SS) on the growth of germinating seeds was investigated. It inhibited root growth more than shoot growth. Chemical analysis of roots indicated that nucleic acids decreased but their elution pattern from a column of methylated albumin kieselghur showed no qualitative differences. SS decreased the number of cells undergoing mitosis per root tip. This number was correlated with root length. One nM N⁵-benzyladenine reversed the effect of SS on both root length and mitosis. Thus the effect of SS appears specific to cell division. SS failed to affect oxidative phosphorylation in isolated mitochondria so its effect on cell division would not be secondary to the inhibition of energy conservation. It s possible inhibition of enzyme activity is selective since it also failed to affect RNase activity in vitro.     

Inhibition of Growth by Amber Suppressors in Yeast

Strains of the yeast Saccharomyces cerevisiae that contain highly efficient amber (UAG) suppressors grow poorly on nutrient medium, while normal or nearly normal growth rates are observed when these strains lose the supressors or when the suppressors are mutated to lower efficiencies. The different growth rates account for the accumulation of mutants with lowered efficiencies in cultures of strains with highly efficient amber suppressors. Genetic analyses indicate that one of the mutations with a lowered efficiency of suppression is caused by an intragenic mutation of the amber supressor. The inhibition of growth caused by excessive suppression is expected to be exacerbated when appropriate suppressors are combined together in haploid cells if two suppressors act with a greater efficiency than a single suppressor. Such retardation of growth is observed with combinations of two UAA (ochre) suppressors (Gilmore 1967) and with combinations of two UAG suppressors when the efficiencies of each of the suppressors are within a critical range. In contrast, combinations of a UAA suppressor and a UAG suppressor do not affect growth rate. Apparently while either excessive UAA or excessive UAG suppression is deleterious to yeast, a moderate level of simultaneous UAA and UAG suppression is not.     

Growth Inhibition of Rhodopseudomonas capsulata by Methylmercury Acetate

Growth of Rhodopseudomonas capsulata was inhibited in a bacteriostatic manner by as little as 10-minus 8 M methylmercury acetate (MeHgAc) in unsupplemented synthetic liquid medium or when cells were exposed to 8.0 nm of MeHgAc per mg of cell protein in a single exposure.     

Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

Growth kinetics, i.e., the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in microbiology. However, despite more than half a century of research, many fundamental questions about the validity and application of growth kinetics as observed in the laboratory to environmental growth conditions are still unanswered. For pure cultures growing with single substrates, enormous inconsistencies exist in the growth kinetic data reported. The low quality of experimental data has so far hampered the comparison and validation of the different growth models proposed, and only recently have data collected from nutrient-controlled chemostat cultures allowed us to compare different kinetic models on a statistical basis. The problems are mainly due to (i) the analytical difficulty in measuring substrates at growth-controlling concentrations and (ii) the fact that during a kinetic experiment, particularly in batch systems, microorganisms alter their kinetic properties because of adaptation to the changing environment. For example, for Escherichia coli growing with glucose, a physiological long-term adaptation results in a change in K_S for glucose from some 5 mg liter⁻¹ to ca. 30 μg liter⁻¹. The data suggest that a dilemma exists, namely, that either “intrinsic” K_S (under substrate-controlled conditions in chemostat culture) or μ_max (under substrate-excess conditions in batch culture) can be measured but both cannot be determined at the same time. The above-described conventional growth kinetics derived from single-substrate-controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in ecosystems. However, in nature, microbial cells are exposed to a wide spectrum of potential substrates, many of which they utilize simultaneously (in particular carbon sources). The kinetic data available to date for growth of pure cultures in carbon-controlled continuous culture with defined mixtures of two or more carbon sources (including pollutants) clearly demonstrate that simultaneous utilization results in lowered residual steady-state concentrations of all substrates. This should result in a competitive advantage of a cell capable of mixed-substrate growth because it can grow much faster at low substrate concentrations than one would expect from single-substrate kinetics. Additionally, the relevance of the kinetic principles obtained from defined culture systems with single, mixed, or multicomponent substrates to the kinetics of pollutant degradation as it occurs in the presence of alternative carbon sources in complex environmental systems is discussed. The presented overview indicates that many of the environmentally relevant apects in growth kinetics are still waiting to be discovered, established, and exploited.