Physiological biochemical and molecular aspects of gamma-aminobutyric acid (GABA): A stress-responsive non-protein amino acid.

摘要

γ-Amino butyric acid (GABA) is a non-protein amino acid widely found in plant tissues that accumulates in response to various environmental stresses. In this study, 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). We found a direct interaction between GABA and the level of nitrate (NO₃−) in the growth medium. Such an interaction affected the NO₃− uptake system as well as the NO₃− accumulation in the tissues. GABA affected the activities of enzymes involved in primary carbon and nitrogen metabolism (nitrate reductase, glutamine synthetase, glutamate synthase, NADP dependent isocitrate dehydrogenase, and phosphoenol pyruvate carboxylase). The effect on primary root growth of a group of ω-amino-acids (β-alanine, glycine, and δ-amino valeric acid) and other amino acids derived from glutamate (aspartate, asparagine, glutamine, L-alanine and glutamate) were tested. All three ω-amino-acids showed a strong inhibitory effect on primary root elongation of Arabidopsis seedlings regardless of the concentration of MS salts. None of the amino acids derived from glutamate, showed any interaction with MS salt concentration of the medium concerning primary root elongation. Targeted gene inactivation, has been used as an approach to study the functional importance of specific genes related to the metabolism of γ-aminobutyric acid (GABA) ( YMR250w, YGR019w, and YBR006w) and their impact in stresses tolerance. In addition, YFL030w, YLR089c, and YDR111c genes that encode alanine glyoxylate aminotransferase, alanine aminotransferase (mitochondrial isoform), and alanine aminotransferase (cytoplasmic isoforms) respectively were disrupted. Yeast cells carrying different genes disruption were tested for sensitivity to salinity, osmotic, oxidative, and heat stresses. Three Arabidopsis cDNA's At-pGAT1, T19P19 and T16C21 which show high homology with the yeast YGR019w gene and the endogenous yeast YGR019w gene were expressed in yeast cells carrying either the YGR019w or YFL030w disruptions. Yeast cell transformed with these transgenes were submitted to the same stress conditions as yeast cells carrying different genes disruption were submitted previously.