Abstract
Aminobutyric acid (GABA), a ubiquitous four-carbon nonprotein, amino acid, is synthesized via glutamate decarboxylation. It accumulates in response to mechanical stimulation through the Ca 2+ /calmodulin activation of gluta- mate decarboxylase. In this study, dark- and light-grown soybean hypocotyl tissues were used to investigate the rela - tionship between mechanical stimulation, GABA synthesis, and growth inhibition. Mechanical stimulation through stroking resulted in a 65% growth inhibition of dark- or light-grown tissue within 1 min. The 24-h growth increment was reduced by 50% or more. Growth inhibition was accompanied by rapid 4- and 10-fold increases in GABA levels in dark- and light-grown tissue, respectively. Treatment of tissue with exogenous GABA raised GABA levels approxi- mately 6-fold, but did not inhibit growth. In addition, lanthanum or blue light treatment of dark-grown tissue reduced growth by over 60% with no increase in GABA levels. The data demonstrate for the first time, that GABA accumula- tion accompanies growth inhibition occurring in response to mechanical stimulation. However, GABA accumulation alone appears insufficient to cause growth inhibition.
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