Zinc induced activation of GABA-shunt in tobacco (Nicotiana tabaccum L.)

• Zn and GABA interaction might have role in the activation of GABA shunt in tobacco.
• Medium and high Zn concentrations affected GABA and glutamate levels differentially.
• Zinc and GABA interaction is necessary in defense against heavy metal stress.

Zinc is among the important heavy metals which play a key role in plant growth and development for this reason, maintenance of its homeostasis is a critical process within the plant cell. Not only deficiency but also excess Zn leads to reduced growth and development, chlorosis, senescence and increased generation of reactive oxygen species. γ-amino butyric acid (GABA) is a neurotransmission inhibitor non-protein amino acid, which accumulates to high levels when plants are subjected to different stresses including heavy metal stress. In the brain cells of animals a direct interaction between GABA, glutamate and Zn was reported which might be valid for a different necessity in plant cells. In the presented study, we tried to understand if there is an interaction between GABA, glutamate and Zn that leads to the activation of GABA-shunt. We treated Nicotiana tabaccum plants with medium (10 μM) and high (100 μM) Zn concentrations and, we analyzed GABA, glutamate levels in relation to GDH and GAD encoding genes’ expression profiles and specific enzyme activities. Medium and high Zn concentrations affected GABA and glutamate levels differentially in accordance the gene expression profiles and activity levels in the short and long term of the experimental period. In conclusion we can speculate that, medium Zn concentration might be responsible for triggering GABA-shunt for activating the protective mechanisms against heavy metal stress however, high Zn concentrations might be related to the activation of programmed cell death due to toxicity.