Differential accumulation of γ–aminobutyric acid in elicited cells of two rice cultivars showing contrasting sensitivity to the blast pathogen.

Intracellular free amino acid pools were quantified in suspension cultured cells of a blast-sensitive and a blast-resistant rice genotype at increasing time after the treatment with Magnaporthe oryzae cell wall hydrolysates. Besides some expected variations in free phenylalanine, a remarkable early increase of γ–aminobutyric acid (GABA) levels was evident in both cultivars. Glutamate decarboxylase activity and protein levels were unaffected. GABA homeostasis was recovered in the sensitive cultivar 48 h after the treatment. On the contrary, a further GABA accumulation and a general increase of most amino acids were found at this later stage in the resistant genotype, which showed a higher decrease of cell viability as a consequence of elicitor addition. Data support a recently-hypothesized role of GABA metabolism in the plant response to fungal pathogens.