The hormones a-naphthaleneacetic acid and kinetin induce
dedifferentiation of root tissue51. 15N-NMR studies demonstrate
that these changes are accompanied by enhanced GABA and reduced
glutamate levels. GABA accumulation is accompanied by efflux
from the cell, suggesting that it might function as an intercellular
signalling molecule13. Treatment of excised sunflower cotyledons
with GABA stimulates ethylene production, mainly by promoting
transcript abundance of 1-aminocyclopropane 1-carboxylic acid
synthase48,52. Thus, the emerging literature suggests that environmental
stresses elevate cytosolic Ca21, which activates GAD and
GABA synthesis, which in turn, binds to receptors, thereby regulating
growth and development. To date, the existence of GABA
receptors remains speculative.