References

12 GABA and GHB Neurotransmitters in Plants and Animals 181
the SSADH deficiency and the accumulation of SSA (Fig. 12.1) and (12.2)
GHB levels might lead to redox imbalance and tissue toxicity. To test the
latter hypothesis the authors aimed at reducing GHB levels utilizing vinyl-
GABA (Vigabatrin; VGB), a specific inhibitor of GABA-T (Fig. 12.1; Lewis
and Wallace 2001). Indeed, VGB was found effective in reducing the levels
of GHB and the symptoms of SSADH deficiency, like it does in animals
(Hogema et al. 2001; Gupta et al. 2002). Moreover, VGB prevented the
accumulation of H2O2 in the ssadh mutant (Fait et al. 2005). Thus, GHB is
tightly linked to ROI levels in plants.
12.4
Conclusions and Future Perspectives
Recent studies reinforce the notion that the neurotransmitters GABA and
GHB may function as signaling molecules in plants, playing a role in modulating
carbon:nitrogen metabolism, energy balance, and redox equilibrium.
Hence, not surprisingly, these two neurotransmitters are associated with
stress responses in plants, as the levels of both change dramatically in
response to stress situations. Moreover, like in animals, GABA seems to
play a role in cell guidance. However, the mode of action of GABA and
GHB in plants is still unknown. Therefore, an effort to identify receptors
of plant neurotransmitters, as well as their intracellular and intercellular
transporters is crucial toward deciphering their functions and mode of
action. Future studies should also attempt to investigate in vivo real-time
dynamics and spatial distribution of neurotransmitters within plant cells
and throughout the plant under different physiological situations. These
cellular studies with the help of functional genomic tools (e.g., mutants)
and other whole-genome approaches are likely to unravel fascinating mechanisms
of neurotransmitter signaling in plants.
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