SPORE GERMINATION AND CARBON METABOLISM IN FUSARIUM SOLANI. II. ENDOGENOUS RESPIRATION IN RELATION TO GERMINATION

Cochrane , V. W., Jean C. Cochrane , C. b . Collins , and F. G. Serafin . (Wesleyan U., Middletown, Conn.) Spore germination and carbon metabolism in Fusarium solani. II. Endogenous respiration in relation to germination. Amer. Jour. Bot. 50(8): 806–814. Illus. 1963.—Endogenous oxygen uptake by ungerminated macroconidia of Fusarium solani f. phaseoli is more than doubled by exogenous ammonium ion and is increased about 7-fold by germination. The respiratory quotient is halved by the provision of ammonia, which has essentially no effect on the endogenous formation of carbon dioxide. Stimulation by azide and 2,4-dinitrophenol suggests that the supply of phosphate acceptors regulates the rate of endogenous respiration. Mercurials poison the endogenous respiration, cyanide accelerates it, and iodoacetate, arsenite, fluoride, and chelating agents have little effect. Respiration is little affected by changes in pH, external phosphate, oxygen concentration, and spore density, within the limits tested. Spore lipid concentration is increased by cultivation in a high-glucose medium, but this variation in lipid content of spores docs not affect the endogenous Qo₂, nor does a high lipid content abolish the requirement for exogenous carbon for germination. Lipid utilization during endogenous respiration accounts for 37% of the loss in dry weight; lipid is also utilized during germination, but such utilization amounts to only about 5% of the carbon requirement. Neither mannitol nor nitrogenous compounds are significant substrates of endogenous respiration. The oxidation of the exogenous substrates tested does not measurably affect the concomitant rate of endogenous respiration. It is proposed that endogenous respiration can contribute to the synthetic processes of spore germination, although quantitatively insufficient to support germination without exogenous carbon. It is also questioned whether the respiratory quotient is an adequate index of the substrate of endogenous respiration.     

Effects of thiamine and pyridoxine on respiratory activity in Saccharomyces carlsbergensis strain 4228

Studies were made to elucidate the relationship among the thiamine-induced growth inhibition, decrease in cellular vitamin B₆ content and respiratory deficiency in Saccharomyces carlsbergensis strain 4228 [Nakamura et al., Biochem. Biophys. Res. Commun. 59, 771–776 (1974)]. Addition of pyridoxine to the thiamine-added culture at the beginning or in the course of cultivation brought about appearance of cytochrome spectra and the increase in the activity of heme-containing enzymes and in respiratory activity (Q _{O 2}). The effects of pyridoxine occurred prior to the restoration of growth. Pyridoxine was effective even in the presence of high levels of glucose in the growth medium (not less than 3%). On the basis of these results, the mechanism of the effects of thiamine and pyridoxine was discussed.     

The roles of carbon dioxide and abscisic acid in the production of ethylene

Since CO₂ is liberated in the conversion of ACC to ethylene, the evidence that ethylene production by plant tissues is actually promoted by CO₂ calls for an explanation. Accordingly, the formation of ethylene by oat (Avena sativa L. cv. Victory) leaves and by apple (Golden Delicious) and pear (Pyrus communis L. cv. Anjou) tissue in very low levels of CO₂ has been studied. The gas chromatograph was modified to measure CO₂ and ethylene at the same time, by reducing both to methane. (Response of the gas chromatograph to CO₂ concentrations is linear.) The work establishes a clear difference between the endogenous production of ethylene and its production from applied ACC, a difference which holds about equally for leaves and for fruit tissue. The difference is in the CO₂ requirement, namely, lowering the CO₂ level by 99% or more decreases the production of ethylene from applied ACC by 50–60%, but it does not decrease, or even slightly increases, its production from endogenous precursors. Thus, while the need for CO₂ has not been explained, it has at least been delimited. The responses to abscisic acid (ABA) also differ, but in the reverse direction, the endogenous production of ethylene being decreased up to 70% by ABA. while the liberation from ACC is promoted about 20%. ABA also promoted the respiratory CO₂ production by 30% or, in presence of 1-aminocyclopropane-1-carboxylic acid (ACC), by over 50%. Inhibition of ethylene production by cobalt or EDTA shows no such differentiation, while inhibition by Na catechol-4,6-disulfonate (Tiron) shows a small difference. It is concluded either that endogenous ethylene is formed by an enzyme system different from that reacting with ACC, or (more likely) that when ethylene arises from endogenous precursors the reaction does not proceed by way of free ACC, but by some activated form of it.     

Effect of light and gibberellic acid on coleoptile and first-foliage-leaf growth in durum wheat (Triticum durum Desf.)

A comparison has been made of the relative effectiveness of light quality and quantity and gibberellic acid (GA₃) treatment on the elongation growth of the coleoptile and the first foliage leaf in durum wheat (Triticum durum Desf. cvs. Cappelli and Creso). The cultivar Creso is a shortstrawed variety carrying the Gai 1 gene on chromosome 4A, which influences both plant height and insensitivity to applied gibberellins. The main conclusions are as follows: 1) coleoptile elongation growth appears to be modulated via the fluencerate-dependent action of a blue-light receptor and via a low energy response of phytochrome; 2) the inhibition of first-foliage-leaf growth depends on the operation of a single blue-light-responsive photoreceptor; 3) high energy blue light produces the same inhibitory effect on the two wheat cultivars, whereas at relatively low fluences of white and blue light, the cultivar Creso is more sensitive; 4) the insensitivity to applied GA₃ exerted by the gene Gai 1 in Creso is independent of light; 5) in Cappelli, the action of light on coleoptiles appears to be independent of the applied GA₃, whereas the hormone is able to change the pattern of growth inhibition of the first-foliage-leaf.Abbreviations BL blue light - FR far-red light - GA gibberellin - GA₃ gibberellic acid - R red light - WL white light     

Inhibition of proton-translocating ATPases of Streptococcus mutans and Lactobacillus casei by fluoride and aluminum

One of the major effects of fluoride on oral bacteria is a reduction in acid tolerance, and presumably also in cariogenicity. The reduction appears to involve transport of protons across the cell membrane by the weak acid HF to dissipate the pH gradient, and also direct inhibition of the F₁F₀, proton-translocating ATPases of the organisms, especially for Streptococcus mutans. This direct inhibition by fluoride was found to be dependent on aluminum. The dependence on aluminum was indicated by the protection against fluoride inhibition afforded by the Al-chelator deferoxamine and by loss of protection after addition of umolar levels of Al³⁺, which were not inhibitory for the enzyme in the absence of fluoride. The F₁ form of the enzyme dissociated from the cell membrane previously had been found to be resistant to fluoride in comparison with the F₁F₀ membrane-associated form. However, this difference appeared to depend on less aluminum in the F₁ preparation in that the sensitivity of the F₁ enzyme to fluoride could be increased by addition of umolar levels of Al³⁺. The effects of Al on fluoride inhibition were apparent when enzyme activity was assayed in terms of phosphate release from ATP or with an ATP-regenerating system containing phosphoenolpyruvate, pyruvate kinase, NADH and lactic dehydrogenase. Also, Be²⁺ but not other metal cations, e.g. Co²⁺, Fe²⁺, Fe³⁺, Mn², Sn²⁺, and Zn²⁺, served to sensitize the enzyme to fluoride inhibition. The differences in sensitivities of enzymes isolated from various oral bacteria found previously appeared also to be related to differences in levels of Al. Even the fluoride-resistant enzyme of isolated membranes of Lactobacillus casei ATCC 4646 could be rendered fluoride-sensitive through addition of Al³⁺. Thus, the F₁F₀ ATPases of oral bacteria were similar to E₁E₂ ATPases of eukaryotes in being inhibited by Al-F complexes, and the inhibition presumably involved formation of ADP-Al-F _inf3 ^sup- complexes during catalysis at the active sites of the enzymes.     

Isolation of cyanobacterial heterocysts with high and sustained dinitrogen-fixation capacity supported by endogenous reductants

A method is described for the preparation of cyanobacterial heterocysts with high nitrogen-fixation (acetylene-reduction) activity supported by endogenous reductants. The starting material was Anabaena variabilis ATCC 29413 grown in the light in the presence of fructose. Heterocysts produced from such cyanobacteria were more active than those from photoautotrophically-grown A. variabilis, presumably because higher reserves of carbohydrate were stored within the heterocysts. It proved important to avoid subjecting the cyanobacteria to low temperatures under aerobic conditions, as inhibition of respiration appeared to lead to inactivation of nitrogenase. Low temperatures were not harmful in the absence of O₂. A number of potential osmoregulators at various concentrations were tested for use in heterocyst isolation. The optimal concentration (0.2M sucrose) proved to be a compromise between adequate osmotic protection for isolated heterocysts and avoidance of inhibition of nitrogenase by high osmotic strength. Isolated heterocysts without added reductants such as H₂ had about half the nitrogen-fixation activity expected on the basis of intact filaments. H₂ did not increase the rate of acetylene reduction, suggesting that the supply of reductant from heterocyst metabolism did not limit nitrogen fixation under these conditions. Such heterocysts had linear rates of acetylene reduction for at least 2 h, and retained their full potential for at least 12 h when stored at 0°C under N₂.     

Osservazioni prellminari sul meccanismo di azione della cocliobolina

Abstract

MECHANISM OF COCHLIOBOLIN ACTIVITY: A PREVENTIVE NOTE. — Coch-liobolin caused leakage of phosphate and organic compounds from corn rootlets and potato discs, at room temperature. The leakage does not occur at 1–5°C, but when potato discs are incubated at this temperature and then thoroughly washed and brought at 25°C, a sharp increase of phosphate may be noticed in the incubation solutions.

Cochliobolin inhibited partially the aerobic respiration of glucose and endogenous carbon in Micrococcus pyogenes var. aureus resting cells. Aerobic respiration of pyruvate, succinate, fumarate and malate was completely inhibited, while the inhibition of lactate and Lketoglutarate respiration required a short lag period. The hydrogen-ion concentration of the media seemed to be an important factor controlling the rapidity of action of the inhibitor, because at pH 4 and 5 at least 120 minutes were required prior any effect could be observed, while only 30 minutes were required at pH 6.

The effects of cochliobolin on Micrococcus resting cells were irreversible In contrast, respiratory activities of acetonic powders were refractory to the substance under aerobic conditions, and oxidation of pyruvate, malate, fumarate, succinate and α-ketoglutarate were not affected by saturated solutions of cochliobolin. It is suggested that the first site of attack is the cell wall-cell membrane unit, altering cell permeability, so that inorganic ions and other cofactors essential to respiration are lost in consequence of the leakage through the cell membrane.     

Rates and properties of endogenous cyclic photophosphorylation of isolated intact chloroplasts measured by CO2 fixation in the presence of dihydroxyacetone phosphate

1. Dihydroxyacetone phosphate in concentrations ? 2.5 mM completely inhibits CO₂-dependent O₂ evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of P_i, but not by addition of 3-phosphoglycerate. In the absence of P_i, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the ¹⁴C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70–95%. Based on these results the mechanism of the inhibition of O₂ evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts.2. Although O₂ evolution is completely suppressed by dihydroxyacetone phosphate, CO₂ fixation takes place in air with rates of up to 65μ mol · mg^?1 chlorophyll · h^?1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation.3. Under anaerobic conditions, the rates of CO₂ fixation in presence of dihydroxyacetone phosphate are low (2.5–7 μmol · mg^?1 chlorophyll · h^?1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2 · 10^?7 M) reaching values of up to 60 μmol · mg^?1 chlorophyll · h^?1. As under these conditions the ATP necessary for CO₂ fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO₂ fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded that only under anaerobic conditions an “overreduction” of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5 · 10^?7 M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO₂ fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO₂ fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation.4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO₂ fixation in presence of dihydroxyacetone phosphate by dibromothymoquinone under anaerobic conditions indicates that plastoquinone is an indispensible component of the endogenous cyclic electron pathway.     

Nodule growth and nitrogen fixation of <Emphasis Type="Italic">Calopogonium mucunoides</Emphasis> L. show low sensitivity to nitrate

It is well established that nitrate is a potent inhibitor of nodulation and nitrogen fixation in legumes. The objective of this study was to demonstrate the relative insensitivity of these processes to nitrate with Calopogonium mucunoides, a tropical South American perennial legume, native to the cerrado (savannah) region. It was found that nodule number was reduced by about half in the presence of high levels of nitrate (15 mM) but nodule growth (total nodule mass per plant) and nitrogen fixation (acetylene reduction activity and xylem sap ureide levels) were not affected. Other sources of N (ammonium and urea) were also without effect at these concentrations. At even higher concentrations (30 mM), nitrate did promote significant inhibition (ca. 50%) of acetylene reduction activity, but no significant reduction in xylem sap ureides was found. The extraordinary insensitivity of nodulation and N₂ fixation of C. mucunoides to nitrate suggests that this species should be useful in studies aimed at elucidating the mechanisms of nitrate inhibition of these processes.     

Inhibition of a respiratory activity by short saturating flashes in Chlamydomonas: Evidence for a chlororespiration

Excitation with short actinic flashes (2 μs) of oxygenated dark-adapted Chlamydomonas cells deposited on a bare O₂ platinum electrode induces an increase of the amperometric signal after the first two flashes. Mass spectrometer experiments performed in the presence of ¹⁸O₂ showed that this signal was not due to the photolysis of water (H₂¹⁶O). The insensitivity of this signal to 10 μM DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), its stimulation by acetate or high O₂ concentration as well as its inhibition by cyanide indicate that these flash-induced changes in O₂ concentration were related to the inhibition of a respiratory process. Because this rather fast inhibition of respiration is insensitive to antimycin A and to salicyl hydroxamic acid, inhibitors of mitochondrial respiration, and because it occurs on a single flash illumination, we conclude that the related respiratory activity takes place inside the chloroplast (chlororespiration) and not in the mitochondria. This interpretation is confirmed by the quite high K_m(O2) of this process (about 23 μM) compared to those measured for the mitochondrial reactions (0.2 μM for the cytochrome oxidase pathway and 5.5 μM for the alternative pathway). In a mutant lacking Photosystem I activity, no photoinhibition of respiration was observed. We conclude from the above results that the light-induced inhibition of chlororespiration is due to the oxidation by Photosystem I activity of electron carriers common to both photosynthetic and chlororespiratory chains.     

Microphotometric determination of enzymes in brain sections

Summary An incubation medium was established for the microphotometric demonstration of glutamate dehydrogenase (Gldh) in cryostat sections of the rat hippocampus which served as an exemplary brain region. The final incubation medium consisted of 100 mM l-glutamic acid monosodium salt, 5 mM NAD, 10 mM sodium azide (NaN₃), 5 mM ADP, 20 mM sodium chloride, 0.15 mM phenazine methosulfate (PMS), 5 mM nitroblue tetrazolium chloride and 22% polyvinyl alcohol (PVA) in 0.05 M Hepes buffer; the final pH was 7.5. — The study showed that in the histochemical demonstration of Gldh the use of relatively high PVA concentrations were necessary to avoid diffusion artefacts because Gldh seems to be only loosely bound to the mitochondrial matrix. The use of NaN₃ as a blocker of the respiratory chain was indispensible, because without NaN₃ most reduction equivalents were lost through the respiratory chain. With PMS as an exogenous electron carrier, the demonstrable Gldh activities increased significantly indicating that, in the case of Gldh, the endogenous NADH tetrazolium reductase was not sufficiently effective. Furthermore, it was shown that Gldh was affected by many small molecules (e.g. activation by sodium ions, inhibition by magnesium and calcium ions) so that minor variations of the incubation conditions may cause major differences in demonstrable activities. Supported by the Deutsche Forschungsgemeinschaft (Ku 541/2-2)     

A comparison of thermo- and skotodormancy in seeds of Lactuca serriola in terms of induction,alleviation, respiration,ethylene and protein synthesis

Lactuca serriola L., which was found to enter skotodormancy at a relatively low temperature, was used to try and ascertain differences in thermo- and skotodormancy.Abbreviations SE standard error - V_T total respiratory rate - V_cyt respiratory rate inhibited by cyanide - V_alt total respiratory capacity inhibited by SHAM and denoted alternate respiration - V_res residual respiration - PMSF phenylmethylsulfonyl fluoride; panacide, 5,5-2,2-dihydroxydiphenylmethane - SHAM salicyl-hydroxamic acid     

Characterization of pedicel β‐glucuronidase activity in developing maize (Zea mays) kernels

A conspicuous endogenous maize (Zea mays L.) β-glucuronidase (GUS) activity was observed in histochemical assays of non-transformed maize kernels, confounding the use of Escherichia coli gusA as a reporter gene. Appearance of the endogenous activity was developmentally dependent and highly tissue-specific, being localized to the upper pedicel (basal maternal kernel) tissues where the black layer forms in the latter stages of kernel development. Pedicel homogenates exhibited GUS activity using either p-nitrophenyl-β-D -glucuronide or 4-methylumbelliferyl-β-D -glucuronide (MUG) as substrates. Pedicel GUS was apparently not the result of endophyte contamination of enzyme isolates since no endophytes could be cultured. The MUG-based activity had a pH optimum of 4 to 5 and was separable into two isoforms by anion exchange chromatography with K_m values for MUG of 2.2 and 2.7 µM for the early- and late-eluting forms, respectively. The pedicel GUS isoforms had very similar characteristics: native M_r of approximately 32000, stimulation by assay at 60°C, inhibition at high ionic strength or in the presence of EDTA and relative insensitivity to the E. coli GUS inhibitor saccharic acid-1,4-lactone. Only the early-eluting form, however, was capable of hydrolyzing the histocbemical GUS substrate 5-bromo-4-chloro-3-indoyl-β-D -glucuronide. Neither isoform exhibited antifungal activity against Fusarium moniliforme. In contrast to the in vitro activity, pedicel endogenous GUS measured histochemically was completely inhibited by saccharic acid-1,4-lactone, unaffected by EDTA and greatly decreased by incubation at elevated assay temperature. A modification of the standard histochemical GUS assay allowed complete suppression of endogenous GUS activity while enhancing E. coli-derived GUS activity in kernels transiently expressing the gusA gene. Possible roles of these endogenous GUS activities within the black layer region of the kernel pedicel are proposed.     

Arginine metabolism of the Antarctic Bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> (King &; Broderip, 1831): an ecophysiological approach

The potential aerobic ATP-generating pathway and the argininolytic capacity of the Antarctic bivalve Laternula elliptica in its main tissues were measured by the specific activity of the enzymes malate dehydrogenase (MDH), citrate synthase (CS) and arginase. The kidney showed the major potential for aerobic ATP-generating pathway and argininolytic capacity. High levels of CS and MDH activities indicated that renal tissue can be involved in activities that require a lot of energy such as excretion of metabolic end products, amino acids catabolism or even gluconeogenic activities related to inter-tissue metabolism. The fact that kidneys are the main site for arginase activity is very unusual for mollusks and could be related to the living habits of L. elliptica. Genetic expression of the L. elliptica renal arginase could be controlling the levels of l-arginine and forming urea in the excretory organ, which may not have its physiological functions directly affected by the seasonal retraction of its siphons. Compared to the bivalve Dreissena polymorpha, renal arginase of L. elliptica is more resistant to inhibition by copper and cadmium. This could be related to naturally high levels of these metals in the Antarctic marine environment and its bioaccumulation in the renal tissue of L. elliptica, as a probable advantage to its environmental adaptation. Different from other Antarctic animals that feed on Krill, the arginase of L. elliptica is much more sensitive to fluoride inhibition. However, diet composition of L. elliptica would be expected to be variable site to site and its high sensitivity to fluoride inhibition may be a matter of concern in areas near ornithogenic soils subjected to ice-melting processes.     

Simultaneous presence of two terminal oxidases in the respiratory system of dark aerobically grown Rhodospirillum rubrum

Rhodospirillum rubrum CAF10, a spontaneous cytochrome oxidase defective mutant, was isolated from strain S1 and used to analyze the aerobic respiratory system of this bacterium. In spite of its lack of cytochrome oxidase activity, strain CAF10 grew aerobically in the dark although at a decreased rate and with a reduced final yield. Furthermore, aerobically grown mutant cells took up O₂ at high rates and membranes isolated from those cells exhibited levels of NADH and succinate oxidase activities which were similar to those of wild type membranes. It was observed also that whereas in both strains O₂ uptake (intact cells) and NADH and succinate oxidase activities (isolated membranes) were not affected by 0.2 mM KCN, the cytochrome oxidase activity of the wild type strain was inhibited about 90% by 0.2 mM KCN. These data indicate the simultaneous presence of two terminal oxidases in the respiratory system of R. rubrum, a cytochrome oxidase and an alternate oxidase, and suggest that the rate of respiratory electron transfer is not limited at the level of the terminal oxidases. It was also found that the aerobic oxidation of cellular cytochrome c ₂ required the presence of a functional cytochrome oxidase activity. Therefore it seems that this electron carrier, which only had been shown to participate in photosynthetic electron transfer, is also a constituent of the respiratory cytochrome oxidase pathway.Abbreviations DCIP 2,6-dichlorophenolindophenol - DMPD N,N-dimethyl-p-phenylenediamine - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)-ethyl]-glycine     

Coenzyme Q-pool function in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria

We have investigated the role of the Coenzyme Q pool in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. Antimycin A and myxothiazol inhibit glycerol-3-phosphate cytochromec oxidoreductase in a sigmoidal fashion, indicating that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III. The inhibition of ubiquinol cytochromec reductase is linear at low concentrations of both inhibitors, indicating that sigmoidicity of antimycin A and myxothiazol inhibition is not a direct property of antimycin A and myxothiazol binding. Glycerol-3-phosphate cytochromec oxidoreductase is strongly stimulated by added CoQ₃, indicating that endogenous CoQ is not saturating. Application of the pool equation for nonsaturating ubiquinone allows calculation of theK _m for endogenous CoQ of glycerol-3-phosphate dehydrogenase of 3.14mM. The results of this investigations reveal that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III in brown adipose tissue mitochondria; moreover, its concentration is far below saturation for maximal electron transfer activity in comparison with other branches of the respiratory chain connected with the CoQ pool. HPLC analysis revealed a lower amount of CoQ in brown adipose mitochondria (0.752 nmol/mg protein) in comparison with mitochondria from other tissues and the presence of both CoQ₉ and CoQ₁₀.     

Studies of insufficient mixing in bioreactors: Effects of limiting oxygen concentrations and short term oxygen starvation on Penicillium chrysogenum

The effect of oxygen limitation on the respiration rate of Penicillium chrysogenum was studied. The results show that measurements of critical oxygen tensions within a process that on morphological or on physical grounds exhibits an inhomogenous structure are not likely to resemble the Monod model.In order to study the effects of short term oxygen starvation on the respiratory capacity of Penicillium chrysogenum, a two compartment fermenter was constructed. This fermenter consists of one well mixed aerobic part (CSTR) and one minor anaerobic part (CPFR). In the latter the circulation time as well as the volume can be varied. After passage of the whole cell culture volume through the anaerobic part, irreversible inhibition of the respiration was observed. This was caused by a circulation time of 5 and 10 min in the plug flow reactor and with a volume of 6% of the stirred tank reactor volume. However, circulation times of 1 and 2 min with an anaerobic zone of 1% of the stirred tank reactor volume did not give any irreversible effects on the respiratory capacity.This was compared with the results of the previously established model ln(1 — I _OUR//100)^–1 = kt [1]. The I _OUR is the percentage irreversible inhibition of the respiration, t is the anaerobic circulation time and k is a constant. The two compartment fermenter results agree with the earlier model at circulation times of 5 and 10 min, but not with the shorter times, and this suggests that a lag phase exists in the inactivation kinetics.     

A mathematical model for the aerobic growth of Saccharomyces cerevisiae with a saturated respiratory capacity

A mathematical model for the aerobic growth of Saccharomyces cerevisiae in both batch and continuous culture is described. It was based on the experimental observation that the respiratory capacity of organism may become saturated and exhibit a maximum specific oxygen uptake rate after suitable adaptation. This experimental observation led to the possibility that transport into and out of the mitochondrion was of major importance in the overall metabolism of S. cerevisiae and was subject to long-term adaptation. Consistent with this observation a distributed model was proposed which. as its basis, assumed the control of repression or inhibition of the uptake rates of other substrates. No other regulation of fermentation and respiration was assumed. The model provided a suitable structure allowing precise quantification of the changes in rate and stoichiometry of energy production. The model clearly indicated that growth under the wide range of experimental conditions reported could not be predicted using constant values for the maximum specific respiratory rate of constant values of Y_ATP (g biomass/mol ATP) and PO ratio of (mol ATP/atom oxygen). The causes of the variation in the respiratory rate were not determined and it was concluded that a more detailed analysis (reported subsequently) was required. The variation of Y_ATP and PO ratio with specific growth rate implied that the efficiency of ATP generation or ATP utilization decreased with increasing specific growth rate. It was concluded that it was not possible to quantify the individual effect of Y_ATP and PO ratio until independent means for their reliable estimation is available.     

Nitrate content and nitrate reductase activity in Rumex obtusifolius L.

Summary The aim of this work was to investigate the effect of nitrogen starvation and subsequent fentilization with nitrate or ammonium on nitrate content and nitrate reductase activity of Rumex obtusifolius L. under natural conditions.When plants were transplanted to nitrate-poor media, endogenous nitrate was reduced within a few days. In parallel, nitrage reductase activities dropped to about 25% of the initial values. As a consequence of nitrate fertilization (1; 10 or 100 mmol KNO₃/l substrate), endogenous nitrate content of the plant abruptly increased within one day. In extreme cases, nitrate concentrations of up to 10% of plant dry weight could be observed without being lethal. High external nitrate concentrations caused an inhibition of nitrate reductase within the leaves, while low external concentrations provoked an increase in the enzyme activity of about 450% within one day. Ammonium fertilization (5 mmol (NH₄)₂SO₄/l substrate) also caused an increase in nitrate reductase activity and nitrate content within leaf blades. This observation indicates a rapid nitrification of ammonium in the substrate. When plants were fertilized with ammonium plus nitrate (2.5 mmol (NH₄)₂SO₄+ 5 mmol KNO₃/l substrate), an extremely high and long term increase in nitrate reduction could be observed. Due to an intensive enzymatic nitrate turnover, the nitrate content of leaf blades then remained relatively low. Our observations do not point to an inhibition of nitrate reductase activity in leaves of Rumex obtusifolius by ammonium. Despite temporarily high endogenous nitrate concentrations, Rumex obtusifolius may not be termed as a nitrate storage plant, since the accumulation of nitrate is a short term process only.