Abstract
The plant growth-promoting rhizobacteria have developed many different (indirect and direct) mechanisms that have a positive effect on plant growth and development. Strains isolated from Astragaluscicer and Astragalusglycyphyllos root nodules were investigated for their plant growth-promoting properties such as production of indole-3-acetic acid (IAA) and siderophores, phosphate solubilization, ACC deaminase activity, and tolerance to heavy metals. IAA production and P-solubilization were frequent features in the analysed strains, while siderophores were not produced by any of them. In this work, we investigated the presence of the acdS genes and ACC deaminase activities in Astragalauscicer and A. glycyphyllos microsymbionts, classified within the genus Mesorhizobium. The results demonstrated that the acdS gene is widespread in the genome of Astragalus sp. microsymbionts; however, none of the tested strains showed ACC deaminase activity. The acdS gene sequence similarity of the analysed strains to each other was in the range from 84 to 99 %. On the phylogram of acdS gene sequences of milkvetch, the symbionts clustered tightly with the genus Mesorhizobium bacteria.Electronic supplementary materialThe online version of this article (doi:10.1007/s00203-016-1243-3) contains supplementary material, which is available to authorized users.
Highlights
One of the mechanisms is connected with production of the phytohormone indole-3-acetic acid (IAA)
It was shown that IAA synthesized by bacteria participates in plant–microbe signalling and contributes in roots proliferation and elongation (Vessey 2003)
It should be noted that bacterial IAA can stimulate the activity of ACC synthetase, thereby increasing ACC synthesis (Glick 2012)
Summary
It is responsible for several processes in plants and, depending on the level, can e.g. promote root initiation, inhibit root elongation, activate plant hormone synthesis, and promote flower wilting. Ethylene is involved in the response to both biotic and abiotic stresses. An increase in ethylene synthesis may accompany for example extreme temperatures, water flooding, drought, radiation, salinity, and presence of various pathogens. It has been described that ethylene affects various stages of symbiosis (Vacheron et al 2013; Glick 2014). Ethylene can inhibit nodule development in different fabacean plants, for example in Phaseolus vulgaris, Lotus japonicas, and Trifolium repens (Tamimi and Timko 2003)
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