Effects of 2,4-Dichlorophenoxyacetic acid, antiauxins, and metabolic perturbations on cytoplasmic and vacuolar pH of corn root tips measured by in vivo 31P-NMR.
Kasai F. | Bayer D.E.
Cytoplasmic pH (pHcyt) and vacuolar pH (pHvac) of corn (Zea mays L. cv Pioneer 3377) root tips measured by in vivo 31P-NMR were typically 7.6 and 5.5, respectively, and both were stable under the external pH variation (6.5 to 4.5). The treatment with 200 micromolar 2,4-Dichlorophenoxyacetic acid (2,4-D) did not affect pHvac and ATP peaks on 31-NMR spectra, but slightly reduced pHcyt. This suggests that 2,4-D accumulation occurs in cytoplasm rather than in vacuoles. Antiauxins 100 micromolar p-chlorophenoxyisobutyric acid (PCIB) and 100 micromolar N-1-naphthylphthalamic acid did not affect pHvac, pHcyt, nor ATP peaks. In contrast, anaerobic conditions and the treatment with an uncoupler. 50 micromolar carbonylcyanide-m-chlorophenylhydrazone, caused a remarkable reduction in pHcyt with decreasing ATP peaks. The pHvac was relatively stable even under these conditions. These results support the hypothesis that metabolic inhibitors inhibit 2,4-D accumulation in plant cells by reducing pHcyt and an antiauxin, PCIB, inhibits 2,4-D accumulation without affecting pHcyt.
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