EFFECTS OF 2,4-DICHLOROPHENOXYACETIC ACID, ANTIAUXINS, AND METABOLIC PERTURBATIONS ON CYTOPLASMIC AND VACUOLAR PH OF CORN ROOT-TIPS MEASURED BY IN-VIVO P-31-NMR

Cytoplasmic pH (pH(cyt)) and vacuolar pH (pH(vac)) of corn (Zea mays L . cv Pioneer 3377) root tips measured by in vivo P-31-NMR were typical ly 7.6 and 5.5, respectively, and both were stable under the external pH variation (6.5 to 4.5). The treatment with 200 mu M 2,4-Dichlorophe noxyacetic acid (2,4-D) did not affect pH(vac) and ATP peaks on P-31-N MR spectra, but slightly reduced pH(cyt). This suggests that 2,4-D acc umulation occurs in cytoplasm rather than in vacuoles. Antiauxins 100 mu M p-chlorophenoxyisobutyric acid (PCIB) and 100 mu M N-1-naphthylph thalamic acid did not affect pH(vac), pH(cyt), nor ATP peaks. In contr ast, anaerobic conditions and the treatment with an uncoupler, 50 mu M carbonylcyanide-m-chlorophenylhydrazone, caused a remarkable reductio n in pH(cyt) with decreasing ATP peaks. The pH(vac) was relatively sta ble even under these conditions. These results support the hypothesis that metabolic inhibitors inhibit 2,4-D accumulation in plant cells by reducing pH(cyt) and an antiauxin, PCIB, inhibits 2,4-D accumulation without affecting pH(cyt). (C) 1995 Academic Press, Inc.