Regulation of dark CO 2 fixation in avena coleoptile sections by α-naphthylacetate and ammonia

Abstract

Concentrations of α-naphthylacetate (α-NA) of 10 μM or higher inhibited dark CO 2 fixation whereas concentrations of NH 4Cl greater than 0.1 mM stimulated dark CO 2 fixation. Inhibition of fixation is not due to the production of α-naphthol or acetate the products of α-NA hydrolysis. Stimulation of fixation is not due to the addition of Cl −. Tests with phosphoenolpyruvate (PEP) carboxylase in vitro suggest that neither inhibition nor stimulation was due to a direct effect on the enzyme responsible for dark CO 2 fixation. The results indicate that growth promotion by α-NA and auxins occurs through different mechanisms. It is suggested that addition of α-NA or NH 3 to etiolated coleoptile tissue influences in vivo PEP carboxylase activity by altering the cytoplasmic pH.