Net H+fluxes from various root zones of Arabidopsis lines treated with auxin transport inhibitor NPA. Measurements were taken from the elongation (A) and mature (B) root zone of Arabidopsis thaliana plants after 24 h of treatment with NPA. Mean ± SE (n = 8). The flux convention is “influx positive”. * significantly different from the control of that genotype (*P < 0.05, t test).