Unusual features of respiration in mixotrophic green tobacco callus tissues

Respiratory activity of green tobacco callus tissue from thepith of Nicotiana tabacum var. Samsun was influenced by light.Interruption in the light period resulted in a decrease in respiratoryactivity after a lag period of about 2 hr. The respiration levelincreased on re-illumination and was restored to its originallevel after 2–3 hr. The light effect that increased respiratory activity was enhancedby sugar in the medium and by increasing the light intensity.However, the response to light was not affected by an inhibitorof photorespiration and was suppressed completely by an inhibitorof photosynthesis. (Received August 9, 1978; )     

Inhibition of DNA polymerases and DNA topoisomerase II by triterpenes produced by plant callus

We found that some triterpene compounds could not only selectively inhibit the activities of mammalian DNA polymerase alpha (pol alpha) and beta (pol beta), but could also potently inhibit DNA topoisomerase II (topo II) [Biochem. J. 350 (2000) 757]. Here, we report that natural triterpenes produced by callus from an ancient Chinese medicinal plant were also inhibitors of the enzymes, and some were more selective than others. The natural triterpenes with a carboxyl group equally inhibited the activities of pol alpha, pol beta, and topo II, while the olide-type triterpenes with a ketone group suppressed the activities of pol beta and topo II, but not pol alpha. The other triterpenes from the callus hardly influenced these enzyme activities. As also described previously [J. Biochem. 130 (2001) 657], pol beta and topo II have a three-dimensionally similar triterpene-binding region, which is a pocket in which specific compounds can insert. The newly found triterpene inhibitors might structure-dependently insert into the pocket, and the pocket structure of each enzyme might, three-dimensionally but slightly, differ among them. The triterpene frames could be used for screening new inhibitors of the enzymes, and computer-simulated drug design using the frame and pocket structure may in theory be a possible approach to develop new inhibitors.     

Inhibition of reproduction of Xyleborus ferrugineus by ascorbic acid and related chemicals

Effects of various dietary chemicals on the reproduction of the ambrosia beetle, Xyleborus ferrugineus were studied. Ascorbic acid, araboascorbic acid, dehydroascorbic acid, hydroquinone, catechol, cysteine, and α-tocopherol each inhibited progeny production by virgin females. Detailed studies of the effects of ascorbic acid showed that it inhibited progeny production by causing a nutritionally detrimental non-enzymic browning of the dietary casein. Amino acid analyses of such browned and unbrowned casein, after in vitro digestion with pepsin and pancreatin, showed that lesser amounts of certain amino acids were released from the browned material. Effects of the non-enzymic browning were overcome by increasing the casein component of the diet. It was further concluded that araboascorbic acid, dehydroascorbic acid, hydroquinone, and catechol probably inhibit reproduction of X. ferrugineus by the same mechanism as ascorbic acid. No explanation of the inhibitory action of α-tocopherol on X. ferrugineus is offered.     

Growth and chlorophyll production in plant callus tissues grown in vitro

Summary Growth, nutrition and chlorophyll development were studied in chlorophyllous callus tissues isolated from the following edible angiospermous plants: carrot root, crown gall of tomato, endive embryo, leaf petiole and stem of lettuce, leaf petiole of parsley, pea stem and rose stem. Growth patterns of these tissues in vitro were sigmoid. Synthetic media produced less growth, in terms of fresh weight increase, than media containing coconut milk, a highly complex and little understood natural substance. Murashige and Skoog's synthetic medium proved useful for satisfactory growth and chlorophyll production in a number of tissues. Its usefulness was further increased by additional amounts of copper sulphate, potassium nitrate and monobasic ammonium phosphate. Increased levels of iron and magnesium inhibited growth. Incorporation of yeast extract in the tobacco-high-salts-medium produced the highest amount of growth and chlorophyll formation in endive tissue. Presence of exogenous sucrose was essential for the continued good growth of the above callus tissues in vitro. Highest amount of growth took place either in white light or in the dark. Different tissues had different responses to high or low intensities of light. Endive and carrot tissues produced in vitro were palatable to human taste. Endive tissue was particularly good as it also differentiated many small rosettes of leaves, shoots and had a mild aromatic flavor typical of the endive plants grown in nature.     

Inhibition of yeast respiration and fermentation by benomyl, carbendazim, isocyanates, and other fungicidal chemicals

The inhibition of yeast (Saccharomyces cerevesiae) metabolism by fungicidal chemicals was investigated. Glucose- or ethanol-dependent yeast respiration was measured with an oxygen electrode, and manometric determination of carbon dioxide release was used to measure fermentation. Both respiration and fermentation were inhibited more by benomyl than by identical molar concentrations of its breakdown product, carbendazim. Butyl isocyanate, another benomyl breakdown product, inhibited respiration more but inhibited fermentation less than the parent compound. Of the isocyanates tested, hexyl isocyanate was the most inhibitory towards both activities. Captan was more active and iprodione less active than benomyl. Because benomyl rapidly broke down to carbendazim when it was prepared in 80% ethanol, only 59% of the dissolved benomyl was intact when it was added to yeast to determine its effect on respiration or fermentation.     

Inhibition by menthol and its related chemicals of compound action potentials in frog sciatic nerves

AimsTransient receptor potential (TRP) vanilloid-1 (TRPV1) and melastatin-8 (TRPM8) channels play a role in transmitting sensory information in primary-afferent neurons. TRPV1 agonists at high concentrations inhibit action potential conduction in the neurons and thus have a local anesthetic effect. The purpose of the present study was to know whether TRPM8 agonist menthol at high concentrations has a similar action and if so whether there is a structure–activity relationship among menthol-related chemicals.Main methodsCompound action potentials (CAPs) were recorded from the frog sciatic nerve by using the air-gap method.Key findings(?)-Menthol and (+)-menthol concentration-dependently reduced CAP peak amplitude with the IC₅₀ values of 1.1 and 0.93 mM, respectively. This (?)-menthol activity was resistant to non-selective TRP antagonist ruthenium red; TRPM8 agonist icilin did not affect CAPs, indicating no involvements of TRPM8 channels. p-Menthane, (+)-limonene and menthyl chloride at 7–10 mM minimally affected CAPs. On the other hand, (?)-menthone, (+)-menthone, (?)-carvone, (+)-carvone and (?)-carveol (in each of which chemicals OH or O group was added to p-menthane and limonene) and (+)-pulegone inhibited CAPs with extents similar to that of menthol. 1,8-Cineole and 1,4-cineole were less effective while thymol and carvacrol were more effective than menthol in inhibiting CAPs.SignificanceMenthol-related chemicals inhibited CAPs and were thus suggested to exhibit local anesthetic effects comparable to those of lidocaine and cocaine as reported previously for frog CAPs. This result may provide information to develop local anesthetics on the basis of the chemical structure of menthol.     

Studies on plant growth-regulating substances: The metabolism of indole-3-acetonitrile and related compounds in wheat and pea tissues

The plant growth-regulating activity of a number of new indole derivatives is reported. It is shown that indole-3-acetonitrile (IAN) is converted to indole-3-carboxylic acid by metabolism within wheat and pea tissues, and the mechanism of this a-oxidation reaction has been studied. The relevant indole compounds were synthesized and their metabolism investigated by T.L.C. techniques. N -Methylindole-3-acetonitrile was also shown to be degraded by a-oxidation in wheat and pea tissues and this was separately investigated. While no definite conclusions can be drawn, the evidence indicates that conversion of indole- and Af-methylindole-3-acetonitriles to the corresponding indole-3-aldehyde-cyanohydrins can occur. These compounds then become metabolized to the aldehydes and then to the respective indole-3-carboxylic acids. Indole- and A⁷-methylindole-3-glyoxylic acids do not appear to be involved in the a-oxidation reaction to any significant extent. Relevant studies on the metabolism of indole-3-acetaldehyde-cyanohydrin are also described.     

The induction of callus in sugareane tissue cultures by selected chemicals

Immature leaf tissue of two commercial clones of sugarcane was subjected to tissue culture in Louisiana and Hawaii. The callus-incuding activity of selected compounds at 2, 4, and 20 mg/l was compared to the activity of 2,4-D at the same concentrations and to tissue on medium without a callus-inducing agent. Of the 79 compounds tested, 25 induced callus and 54 were ineffective. Ninety-six percent of the effective compounds were in chemical groups with known auxin activity. The results suggested that simple ring structure, phenol derivatives, or a halogenated hydrocarbon chain are not sufficient to induce callus. When callus was transferred to a medium lacking the inductive chemical, differentiation into shoots, roots, or both occurred in callus produced by 80% of the effective compounds.     

Vitamin D and related compounds as plant growth substances

Vitamin D and related compounds (hydroxylated derivatives and glycosides) occur naturally in certain plants. The metabolism of vitamin D₃ in Solanum malacoxylon Sendtn. is similar in certain respects to that in animal systems. There is also evidence that vitamin D₃, plays a role in processes regulated by Ca²⁺ in plants. Vitamin D₃ possesses plant growth substance activities and in particular enhances adventitious root formation.     

Inhibition of respiration in yeast by light

Irradiation of starved cultures of Saccharomyces cerevisiae with blue light under aerobic conditions inhibited the capacity of the yeast cells to respire added substrates (e.g., ethanol) and stimulated endogenous respiration. Spectroscopic examination of the cells showed that the irradiation destroyed both cytochrome a and a₃ components of cytochrome oxidase and a part of the cytochrome b. Irradiation under anaerobic conditions had no effect on the respiratory capacity or the cytochrome content of the cells. Under aerobic conditions cytochrome a₃ was protected against photodestruction when complexed with cyanide and cytochrome a was protected when complexed with azide.     

Inhibition of plant telomerase by telomere-binding proteins from nuclei of telomerase-negative tissues

The activity of telomerase in plant cells is precisely regulated in response to changes in cell division rate. To explore this regulatory mechanism, the effect on telomerase activity of protein extracts from nuclei of telomerase-negative tissues was examined. An inhibition of telomerase activity was found which was species-non-specific. This inhibition was due to proteins which form salt-stable, sequence-specific complexes with the G-rich telomeric strand and reduce its accessibility, as shown by gel retardation and by terminal transferase (TdT) extension of G-rich telomeric and non-telomeric (substrate) primers. A 40 kDa polypeptide was detected by SDS-PAGE after cross-linking the complex formed by extracts from tobacco leaf nuclei. Such proteins may be involved in regulation of telomerase activity in plants.     

Inhibition of photosynthesis and respiration by batatasins

Effects of batatasins I, III and V, phenolic growth inhibitors occuring in dormant bulbils of Dioscorea batatas Decne., on photosynthetic reactions of chloroplasts from spinach (Spinacia oleracea L.) and on respiration of mitochondria from potatoes (Solanum tuberosum L.) were investigated. In chloroplasts, the batatasins effectively inhibited CO₂-dependent oxygen evolution and electron flow from water to acceptors such as dichlorophenolindophenol, ferricyanide and methylviologen. Photosystem-I dependent electron transport from ascorbate to oxygen was stimulated. The proton conductivity of thylakoid membranes was increased and phosphorylation was uncoupled from electron transport. Inhibition of electron transport with water as electron donor appeared to precede uncoupling. In mitochondrial, batatasin I did not much inhibit succinate-dependent O₂ uptake in the absence of ADP, but caused strong inhibition in the presence of ADP. Batatasins III and V inhibited oxygen uptake irrespective of the presence or absence of ADP. Inhibition of chloroplast and mitochondrial reactions by batatasins was shown to be reversible.Abbrevations B-I batatasin I, 6-hydroxy-2,4,7-trimethoxyphenanthrene - B-III batatasin III, 3,3-dihydroxy-5-methoxybibenzyl - B-V batatasin V, 2-hydroxy-3,4,5-trimethoxybibenzyl - Chl chlorophyll - MV methylviologen - DCPIP 2,6-dichlorophenol-indophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PVP polyvinylpyrrolidone     

Inhibition of mitochondrial respiration by mepivacaine

In the last years our researches on neurotropic drugs follow our hypothesis that the strong effects on nervous system have always hidden more widespread effects on all tissues and cells. It is often required to employ local anesthetics in practising dentistry and orthodontics, particularly when children have to be treated. We have assayed in vitro one of these dental anesthetics, mepivacaine, on liver rat mitochondria: it depresses the respiration coupled to phosphorylation in mitochondria having a good respiratory control; so respiratory control too is depressed, but P/O ratio is unaffected; also respiration uncoupled by 2.4-dinitrophenol is depressed. Depressing respiration cooperates with anesthesia; unchanging P/O is good for the health of the cells and tissues treated by the mepivacaine.