Microbial odors found to promote plant growth

A research group including Professor Akihiro Ueda, Associate Professor Hisashi Omura, and Assistant Professor Mami Nampei at the Graduate School of Integrated Sciences for Life, Hiroshima University, revealed how volatile compounds released by soil microorganisms promote the growth of Arabidopsis thaliana. This is expected to lead to the development of new plant growth promoters (biostimulants) and applications to agriculture. The findings were published in the Journal of Experimental Botany on June 24.

Plant growth-promoting substances released by beneficial microorganisms are known as biostimulants and are expected to have a wide range of agricultural applications. Therefore, the research group searched for substances possessing plant growth-promoting functions from among microbial volatile organic compounds (mVOCs) emitted by microorganisms.

The researchers co-cultured Arabidopsis and microorganisms in separate compartments of Petri dishes, allowing exposure only to microbial volatiles, and screened for strains that promoted plant growth. Five of the 70 microbial strains tested were found to promote the growth of A. thaliana. They identified bacterial species via 16S rDNA analysis.

Next, by performing comprehensive analysis of emitted mVOCs, they detected a total of 172 types. Among the compounds commonly released by these microorganisms, the volatile compound 2,5-dimethylpyrazine was found to promote the growth of A. thaliana. This compound occurs naturally in foods such as asparagus, raw peanuts, green tea, roasted coffee, and roasted meat, and is known for its characteristic roasted, nut-like aroma. When plants were exposed to the compound, nitrogen levels increased in the shoots, while genes involved in nitrate and ammonium uptake became more active in the roots.

To investigate how 2,5-dimethylpyrazine promotes plant growth, the researchers conducted ionomic analyses of essential elements within the plants. The analyses revealed increased nitrogen levels in the shoots, along with higher concentrations of chlorophyll and carotenoids, pigments essential for photosynthesis.

In addition, as a result of quantitative gene expression analysis via real-time PCR, expression induction of gene groups encoding nitrate transporters and ammonia transporters was observed. It was found that growth is promoted by improving acquisition capabilities for nitrogen nutrients such as nitrate and ammonia.

Ueda commented, "The fascinating aspect of this research is that we still do not know where many plant growth-promoting microorganisms are found. As a result, researchers continue collecting samples from a wide range of environments in search of new beneficial microorganisms. In addition, research on 'odors (volatile organic compounds)' emitted by microorganisms is also an extremely interesting field. Even for types or extremely low concentrations of volatile substances that cannot be perceived by human olfaction, they can greatly influence plant growth. I think new useful microorganisms and useful substances will still be found."

Journal Information
Publication: Journal of Experimental Botany
Title: Microbial volatile organic compound enhances Arabidopsis growth through activation of nitrate and ammonium transport
DOI: 10.1093/jxb/erag076