Eike Libbert

Pathways of IAA Production from Tryptophan by Plants and by Tbeir Epipbytic Bacteria: a Comparison: I. IAA Formation by Sterile Pea Sections in vivo as Inftuenced by IAA Oxidase Inbibitors and by Transaminase Coenzyme.

Under nonsterile conditions, IAA can be extracted from pea stem sections infiltrated with buffer, IAA, or tryptophan. This IAA has microbial origin, since its occurrence is prevented by antibiotics. All infiltrated IAA disappears in the sections. Under sterile conditions, several inhibitors of IAA oxidase prevent the complete disappearance of infiltrated IAA. Some of them permit, by preventing the disappearance of produced IAA, the formation in vivo of extractable IAA amounts from tryptophan. This IAA production is further increased by pyridoxal (phospbate), and by α-ketoglutarate.

Pathways of IAA production from tryptophan by plants and by their epiphytic bacteria: Metabolism of indolepyruvic acid and indolelactic acid

Metabolites of indolepyruvic acid and indolelactic acid were investigated using 2 systems: a bacterial (pea stem homogenates containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). The products of spontaneous indolepyruvic acid decomposition in aqueous solution and during chromatography were investigated, too.Biological indolepyruvic acid conversion yields, besides those substance amounts which occur spontaneously, indoleacetic acid, indoleethanol (tryptophol) and (only in the sterile plant system) indoleacetaldehyde. An inhibitor extract from pea stems decreases the indoleacetic acid and increases the indoleethanol and indoleacetaldehyde gain.Indolelactic acid is not metabolized in the sterile plant sections. Indolelactic acid oxidation by the bacteria-containing homogenate yields indolepyruvic acid and is inhibited by the inhibitor extract.AbstractMetabolity kys. indolylpyrohroznové a kys. indolylmléčné byly studovany za pomoci 2 systémů: bakteriálního (homogenáty stonků hrachu obsahujících epifytické bakterie) a rostlinného (sekce stonků hrachu vypestovaného za sterilních podmínek). V laboratorních podmínkach byly rovnež sledovány produkty spontanního rozkladu kyseliny indolylpyrohroznové ve vedném roztoku a v průběhu chromatografie.Biologická přeměna kys. indolylpyrohroznové poskytuje vedle látek, které se tvoří spontánně, kyselinu indolyloctovou, indolylethanol (tryptofol) a (jen ve sterilním prostředí) indolylacetaldehyd. Extrakt inhibitoru ze stonků hrachu snižuje kys. indolyloctovou a zvyšuje tvorbu indolylethanolu a indolylacetaldehydu. Kys. indolylmléčná není metabolizována ve sterilních sekcích rostlin. Oxydací kys. indolylmléčné homogenátem obsahujícím bakterie se tvoří kys. indolylpyrohroznová; tato oxydace je inhibována extraktem s nativním inhibitorem.

Beziehungen zwischen Pflanzen und epiphytischen Bakterien hinsichtlich ihres Auxinstoffwechsels: XI. Der Einfluß von IES-bildenden, IES-abbauenden und IES-neutralen Bakterien auf den Auxingehalt der Maispflanze im Vergleich zur Wirkung von Zucker-, Aminosäure- oder Vitaminapplikationen

Summary This investigation was undertaken to decide whether epiphytic bacteria increase the auxin content of their host plant only by giving off IAA, or also by supplying other metabolites, which could affect the auxin content directly or indirectly. 29 different but not identified bacteria strains were isolated from shoots, roots, and from the hydroculture medium of corn plants. The production of IAA from tryptophan and the degradation of IAA by these epiphytic bacteria of corn plants has been investigated. 5 strains were able to produce IAA from tryptophan without being able to destroy it, 6 strains could destroy IAA but not produce it, 13 strains had both properties, and 5 strains behaved indifferent to IAA. More extractable and diffusible auxin was received from sterilized corn plants which were artificially reinfected with epihphytic IAA-producing bacteria strains than from sterile corn plants. Reinfection with strains unable to produce IAA was ineffective, this comes true in the cases of both IAA-indifferent strains and of IAA-destroying ones. This result underlines the causal connection between bacterial IAA production and auxin increase in the host plant. Simultaneous reinfection of the sterile plant material with both an IAA-producing and an IAA-destroying strain did not affect the auxin content. An application of tryptophan increased the auxin content of corn plants which were artificially reinfected with IAA-producing bacteria strains, whereas it was ineffective in the case of plants having been reinfected with IAA-destroying or IAA-indifferent strains. This result, too, corroborates the significance of bacterial IAA production for the bacteria-mediated increase of the auxin level. Application of glucose, glutamic acid, and tyrosine did not result in any influence on the auxin content of sterile, nonsterile or reinfected plants, neither by being converted into a metabolite influencing auxin metabolism, nor by stimulating bacterial growth. Obviously another factor, possibly tryptophan, limits the bacterial effect on the auxin content of the plant. Application of thiamine, riboflavine, and pyridoxal-5’-phsophate did not affect the auxin content of sterile plants. Therefore these potential bacterial metabolites are without significance for the bacteria-induced auxin increase. Application of niacide, on the other hand, considerably increased the auxin content of sterile plants. But the results of another investigation (M anteuffel , S iegl 1973) prove niacide not to be a bacterial metabolite influencing the auxin content under our experimental conditions. The results of the present investigation confirm the supposition that the IAA production by epiphytic bacteria is physiologically significant in enhancing the auxin level in the host plant.

Beziehungen zwischen Pflanzen und epiphytischen Bakterien hinsichtlich ihres Auxinstoffwechsels: XIII. Bakterielle Auxinsynthese in Pflanzenexsudaten

Summary Previous own results demonstrated a connection between IAA production by epiphytic bacteria and the auxin level in the host plant, suggesting the following circuit of substances: plant ⟶ plant exudate (tryptophan) ⟶ epiphytic bacteria ⟶ bacterial product (auxin) ⟶ plant. Now we isolate distinct steps of this circuit from their natural environment, the plant surface. Leachates from sterile coleoptiles or whole plants of maize promote the growth of the epiphytic bacteria strains S 32 and S 42, the degree of this promotion raising with increased duration of washing the plants for receiving the leachates. The bacteria utilize the tryptophan contained in the leachate, and produce an auxin which, with regard to its Rf value, seems to be IAA. The maximal velocity of bacterial auxin production is reached during the stationary phase of bacterial growth, when the main amount of tryptophans has been already consumed. In artificial culture media, representing a mixture of carbohydrates and amino acids quantitatively adopted from the known composition of the natural maize exudate, the bacteria are likewise able to produce auxin, even when thryptophan was omitted. After having been used as bacterial culture medium, maize leachates were filter-sterilized and fractionated by ether extraction. The application of the ether soluble fraction to sterile maize plants results in a clearly elevated content of diffusible auxin in the plant as detected by use of the Avena curvature test. Application of an IAA solution leads to a similar response, whereas the ether unsoluble fraction is ineffective. The bacteria-produced ether soluble material which increases the auxin content of the maize plant seems to be IAA. By washing maize plants with ether for only one minute considerable, obviously bacteria-produced auxin amounts are obtainable from nonsterile but not from sterile plant surfaces, especially after treating the surfaces with tryptophan. Our results underline the supposition the auxin production by epiphytic bacteria is physiologically significant in increasing the auxin level in nonsterile plants under natural conditions.

The role of indoleacetaldehyde in IAA production from tryptophan by plants and by their epiphytic bacteria

Tryptophan, tryptamine, or indolepyruvic acid were applied to 2 systems: a bacterial (pea stem sections containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions).In the plant system, the production of indoleacetic acid and indoleethanol (tryptophol) from each applied indole derivative is clearly reduced by the aldehyde reagents bisulfite and dimedon, respectively. Indoleacetaldehyde is chromatographically detected after alkaline liberation from its bisulfite addition product.In the bacterial system, the production of indoleacetic acid and indoleethanol is likewise reduced by bisulfite and dimedon. However, after tryptophan or tryptamine application, we could not detect indoleacetaldehyde in the described way.In one case only, namely tryptamine application to the bacterial system, indoleethanol production (contrary to indoleacetic acid production) is scarcely reduced by the aldehyde reagents. This indicates a bacterial pathway tryptamine → indoleethanol which bypasses indoleacetaldehyde.AbstractTryptophan, tryptamin nebo kyselina indolylpyrohroznová byly aplikovány na dva systémy: bakteriální (řízky z osy hrachu obsahující epifytické bakterie) a rostlinný (řízky z osy hrachu za sterilnich podmínek).V rostlinném systému byla tvorba indolyloctové kyseliny a indolyletanolu (tryptofolu) ze všech použitych indolových derivátů zřetelněi snízena v přitomnosti činidel na aldehydy, a to bisulfitu a dimedonu. Indolylacetaldehyd byl chromatograficky detegovan po uvolněnè z addičních sloučenin bisulfitu v alkalickém prostředí.V bakteriálmích systémech byla tvorba indolyloctove kyseliny a indolyletanolu bisulfitem a dimedonem rovnéž snižovana. Po aplikaci tryptofanu nebo tryptaminu se však nepodařilo uvedenym způsobem indolylacetaldehyd detegovat.Pouze v jednom připadě, a to při aplikaci tryptaminu na bekteriálnš systém, produkce indolyletanolu (oproti produkci kyseliny indolyloctové) takřka nebyla snízena činidly na aldehydy, což svědči o torn, že v bakteriálním systému cesta metabolické přeměny tryptaminu v indolyletanol obchází indolylacetaldehyd.

Sites and mode of action of a native inhibitor from Pisum sativum affecting the biogenesis of auxin.

Summary A nonacidic inhibitor from pea plants possessing regulatory function in apical dominance was investigated with respect to its effect on the metabolism of indole compounds in 2 experimental systems: a bacterial (pea stem homogenates containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). The inhibitor affects the oxidation of indoleacetaldehyde resulting in decreased IAA and increased indoleacetaldehyde and indoleethanol (tryptophol) formation. Six further inhibitoraffected sites are detected in the bacterial, only two of them in the plant system (see figures 2 and 3). The inhibitor action as well as the similar one of authentic sulfhydryl inactivators (iodoacetate, arsenite) are counteracted by the sulfhydryl donator cystein.