Tryptophan-dependent biosynthesis of auxins in soil

Abstract

The presence of auxins in soil may have an ecological impact affecting plant growth and development. A rapid and simple colorimetric method was used to assess California soils for their potential to produce auxins upon the addition of L-tryptophan (L-TRP). The auxin content measured by colorimetry was expressed as indole-3-acetic acid (IAA)-equivalents. A substrate (L-TRP) concentration of 5.3 g kg 1, glucose concentration of 6.7 g kg -1, no nitrogen, pH 7.0, 40°C, shaking (aeration) and 48 h incubation time were selected as standardized conditions to assay for auxin biosynthesis in soil. IAA was confirmed as a major microbial metabolite derived from L-TRP in soil by use of high performance liquid chromatography (HPLC). Under standardized conditions, L-TRP-derived auxins in 19 soils varied greatly ranging from 18.2 to 303.2 mg IAA equivalents (auxins) kg -I soil. This study suggests that the phenotypic character of the soil microbiota has more of an influence on auxin production than the soil physicochemical properties (e.g., pH, organic C content, CEC, etc.).

ACC-deaminase and/or nitrogen-fixing rhizobacteria and growth response of tomato (Lycopersicon pimpinellfoliumMill.)

“…The number of µmol of α-ketobutyrate produced by this reaction was determined by comparing the absorbance at 540 nm (Honma & Shimomura 1978). Auxin production of the selected rhizobacterial isolates as IAA-equivalents in the presence and absence of L-TRP was examined spectrophotometrically by using Salkowski coloring reagent (Sarwar et al 1992). Some pertinent characteristics of the experimental rhizobacteria are shown in Table 2.…”

Antifungal Activity and Genetic Diversity of Selected Endophytic Fluorescent Pseudomonads

“…On the other hand, the strain SAW23which was identified as Pseudomonas corrugata produced the lowest auxin value (7.84 mgl -1 ). The differences in the performance of auxin-producing fluorescent pseudomonads may be attributed to the inherent properties of the individual bacteria (Sarwar et al, 1992). Similar results regarding variation in the ability to biosynthesize auxin among fluorescent pseudomonads, many investigators also have reported that auxin production by microbial isolates greatly varied within species and/or strains of the same species (Asghar et al, 2002;Khalid et al, 2004;Ahmed et al, 2005).…”

“…Detection of hydrogen cyanide Production of hydrogen cyanide was detected using the method of (Reddy et al, 2008). Indole acetic acid (IAA) production IAA production by the selected fluorescent pseudomonad was detected qualitatively by the modified method as described by (Brick et al, 1991) and quantitatively in the presence of L-tryptophan (L-TRP) by colorimetric method (Sarwar et al, 1992). Phosphate solubilizing activity…”

Azotobacter and L-tryptophan Application for Improving Wheat Yield

“…The contents of the tubes were then filtered through Whatman No. 2 filter paper and auxin production (indole acetic acid equivalents) was measured colorimeterically at 535 nm as described by Sarwar et al (1992).…”

“…The production of plant growth regulators (PGRs) is considered one of the most plausible mechanisms to explain the beneficial effects of Azotobacter Frankenberger, 1991, 1993;Frankenberger and Arshad, 1995;Zahir et al, 1997). The ability of Azotobacter to produce PGRs has been reported and confirmed by various workers (Sarwar et al, 1992;Frankenberger and Arshad, 1995). L-Tryptophan is considered an efficient physiological precursor of auxins in higher plants as well as for microbial biosynthesis of auxins and the possible pathways are well documented in literature (Arshad and Frankenberger, 1997;Frankenberger and Arshad, 1995).…”