Orchid-associated bacteria produce indole-3-acetic acid,promote seed germination,and increase their microbial yield in response to exogenous auxin |
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Authors: | Elena A Tsavkelova Tatiana A Cherdyntseva Svetlana Yu Klimova Andrey I Shestakov Svetlana G Botina Alexander I Netrusov |
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Institution: | (1) Department of Microbiology, Biological Faculty, Moscow State University, Lenin’s Hills, 1/12, 119992 Moscow, Russia |
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Abstract: | Germination of orchid seeds is a complex process. In this paper we focus on interactions between the host-plant and its bacterial
partners via indole-3-acetic acid (IAA). Originally isolated from the roots of the epiphytic orchid Dendrobium moschatum, the strains of Rhizobium, Microbacterium, Sphingomonas, and Mycobacterium genera were among the most active IAA producers. Addition of exogenous tryptophan significantly enhanced auxin formation
both in mineral and complex media. The presence of IAA and indole-3-acetaldehyde was confirmed by HPLC. Indole-3-pyruvic and
indole-3-lactic acids were also detected in supernatants of culture filtrates of Sphingomonas sp., Rhizobium sp., and Microbacterium sp., while indole-3-acetamide was identified only in Mycobacterium sp. Some concentration- and strain-dependent effects of exogenous IAA on bacterial development were also established. Treatment
of the cultures with 10 and 100 μg/ml of auxin resulted in an increase in microbial yield. None of the investigated strains
was able to utilize IAA as a source of carbon and energy. Furthermore, inoculation of D. moschatum seeds with Sphingomonas sp. and Mycobacterium sp. resulted in considerable enhancement of orchid seeds germination. This growth-promoting activity was observed in the
absence of any plant growth stimulators or mycorrhizal fungi, usually required for orchid germination. |
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Keywords: | Associative bacteria Indole-3-acetic acid Orchids Seed germination |
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