Physiological analysis of heterozygous *nhr1* mutant seedlings. Effects of an inhibitor of polar auxin transport and hormones on wild-type and heterozygous *nhr1* seedlings root growth. Seedlings grew on NM for 4 d and were transferred to media containing various concentrations of NPA (A), 2,4-dichlorophenoxyacetic acid (2,4-D; B), 1-naphtalene acetic acid (NAA; C), or ABA (D). Four days later, root growth was measured and plotted as a percentage of root growth on NM. A, Roots of heterozygous *nhr1* seedlings were resistant to the growth-inhibiting properties of NPA. The difference was significant at 10 and 50 μm (Student's *t* test, *P* = 0.01, *P* = 0.0055). B, The auxin 2,4-D equally inhibited root growth in both heterozygous *nhr1* and wild-type seedlings. C, The growth of heterozygous *nhr1* roots showed decreased sensitivity to NAA. The difference was significant at 0.01 and 0.3 μm NAA (Student's *t* test, *P* = 0.001, *P* = 0.02). D, Roots of heterozygou*s nhr1* seedlings were resistant to the growth-inhibiting properties of ABA. The difference was significant at 1 and 10 μm ABA (Student's *t* test, *P* = 0.09, *P* = 4 × 10^{−5}). Error bars represent the mean ± sd (*n* = 15). Absence of bar indicates that sd was less than the thickness of the symbol. The graphs are representative of three independent experiments.

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