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Our laboratory is focused on the enigma of plant 4-aminobutyrate (GABA). Rapid and large accumulations of GABA have been observed in response to a wide variety of plant stresses, biotic and abiotic. GABA accumulation is now known to result from activation of the enzyme GAD which catalyses the decarboxylation of L-glutamate to yield GABA and CO2. GAD is activated by increases in the cytosolic levels of H+ or Ca2+. However, the roles of GABA accumulation are not clear. Presently, we are working on the hypothesis that GABA accumulation is an induced defence against plant-eating insects. GABA is an inhibitory neurotransmitter in animals. We have demonstrated that: 1. Insects crawling on leaves stimulate GABA levels; 2. The stimulus is delivered via the insect footprint; and 3. Raised GABA levels deter feeding.
Crawford LA, Bown AW, Breitkreuz KE, Guinel FC. 1994. The synthesis of gamma-aminobutyric acid in response to treatments reducing cytosolic pH. Plant Physiol. 104:865-871.
Ramputh AI, Bown AW. 1996. Rapid gamma-aminobutyric acid synthesis and the inhibition of the growth and develpment of oblique—banded leaf-roller larvae. Plant Physiol. 111:1349-1352.
Cholewa E, Cholewinski A, Shelp BJ, Snedden WA, Bown AW. 1997. Cold-shock stimulated gamma-aminobutyric acid synthesis is mediated by an increase in cytosolic Ca2+, not by an increase in cytosolic H+. Can. J. Bot. 75: 375-382.
Bown AW, Shelp BJ. 1997. Update on Biochemistry: The metabolism and functions of gamma-aminobutyric acid. Plant Physiol. 115: 1-5.
Shelp BJ, Bown AW, McLean MD. 1999. Metabolism and functions of gamma-aminobutyric acid. Trends Plant Sci. 4: 446-452.
Janzen DJ, Allen LJ, MacGregor KB, Bown AW. 2001. Cytosolic acidification and GABA synthesis during the oxidative burst in isolated mesophyll cells. Can. J. Bot. 79: 438-443.
Bown AW, Hall DE, MacGregor KB. Insect footsteps initiate plant resistance responses within 20 seconds. Submitted.