Evidence for production of the phytohormone indole-3-acetic acid by cyanobacteria

Abstract

The ability of cyanobacteria to produce the phytohormone indole-3-acetic acid (IAA) was demonstrated. A colorimetric (Salkowski) screening of 34 free-living and symbiotically competent cyanobacteria, that represent all morphotypes from the unicellular to the highly differentiated, showed that auxin-like compounds were released by about 38% of the free-living as compared to 83% of the symbiotic isolates. The endogenous accumulation and release of IAA were confirmed immunologically (ELISA) using an anti-IAA antibody on 10 of the Salkowski-positive strains, and the chemical authenticity of IAA was further verified by chemical characterization using gas chromatography-mass spectrometry in Nostoc PCC 9229 (isolated from the angiosperm Gunnera) and in Nostoc 268 (free-living). Addition of the putative IAA precursor tryptophan enhanced IAA accumulation in cell extracts and supernatants. As the genome of the symbiotically competent Nostoc PCC 73102 contains homologues of key enzymes of the indole-3-pyruvic acid pathway, a transaminase and indolepyruvate decarboxylase (IpdC), the putative ipdC gene from this cyanobacterium was cloned and used in Southern blot analysis. Out of 11 cyanobacterial strains responding positively in the Salkowski/ELISA test, ipdC homologues were found in 4. A constitutive and possibly tryptophan-dependent production of IAA via the indole-3-pyruvic acid pathway is therefore suggested. The possible role of IAA in cyanobacteria in general and in their interactions with plants is discussed.

Indole-3-acetic acid: A widespread physiological code in interactions of fungi with other organisms

“…The ability of cyanobacteria to produce IAA was demonstrated; however, whether green algae have IAAproducing ability remains a controversial topic. [72][73][74] In algal strains (Chlorella sp. ), low IAA levels can considerably promote growth and influence oil content.…”

Association of non-heterocystous cyanobacteria with crop plants

“…There are many reports of auxin production by cyanobacteria, mainly referring to indole-3-acetic acid (IAA), which is generally synthesized through a tryptophan-dependent pathway (Sergeeva et al 2002;Tarakhovskaya et al 2007). Auxin-like substances were determined in the culture media by Salkowski reagent.…”

“…Moreover, some cyanobacteria may produce plant growth-promoting substances (Sergeeva et al 2002). There is currently great interest in developing new associations between cyanobacteria and crop plants (Nilsson et al 2005;Rai and Bergman 2002).…”

Growth and biochemical characterization of associations between cyanobionts and wheat seedlings in co-culturing experiments

“…Our results showed that the studied cyanobionts, tryptophan acts as precursor for the synthesis of IAA, followed by its excretion into their surrounding environments. This takes place both in the presence or absence of light, indicating that these cyanobionts possess genes for IAA biosynthesis (Sergeeva et al 2002). The ability to synthesize plant hormones is believed to be a major property of rhizospheric, epiphytic and symbiotic bacteria/cyanobacteria that not only stimulate plant growth, but also play important role as signals in communication between plant host(s) and the relevant microflora (Kravechenko et al 2004;Tsavkelova et al 2006).…”