GABA Increases the Rate of Nitrate Uptake and Utilization in Arabidopsis Roots

TLDR: The authors found that exogenously applied GABA had an effect on root growth and development in Arabidopsis thaliana L. seedlings, and the primary effect was found to be a direct interaction between GABA and the level of nitrate (NO3) in the growing medium.

Abstract: GABA (4-aminobutyric acid) is a non-protein amino acid widely found in plant tissues that accumulates in response to various environmental stresses including heat, cold, drought, salinity, and anaerobic stress. Although there is limited information on its biological function in plants, some studies suggest that GABA acts as a carbon and/or nitrogen source in microorganisms, and it has been suggested that GABA metabolism under stress is related to excessive glutamate accumulation and/or cytoplasmic pH regulation. We found that exogenously applied GABA had an effect on root growth and development in Arabidopsis thaliana L. seedlings. This effect was modulated between inhibition of root elongation when seedlings were grown on full strength Murashige and Skoog salts (1/1X MS) to stimulation of root elongation when plants were grown on 1/8 strength MS salts (1/8X MS). When the concentration of single ions in MS salts was varied, the primary effect was found to be a direct interaction between GABA and the level of nitrate (NO3) in the growing medium. At NO3 concentrations below 40 mM, root growth was stimulated by the addition of GABA to the growth medium, whereas at concentrations above 40 mM NO3 addition of GABA to the growth medium inhibited root elongation. The uptake of NO; and tissue levels of nitrate were also investigated at high (40 mM NO3) and low (5 mM NO,) with and without GABA in the growing medium. In correlation with the growth results GABA promotes NO3 uptake at low NO3, while GABA inhibits NO3 uptake at high NO3. However, tissue levels of NO3 are increased by GABA at high NO3 while they are decreased by GABA at low NO3. These results can be interpreted to indicate that GABA produced during stress is capable of regulating NO3 uptake and metabolism during stress.