Effects of N-1-naphthylphthalamic Acid and Exogenous IAA and GA_3 on the Elongation and Gravitropic Responses of Arabidopsis Roots

The seedlings of Arabidopsis were treated with N-1-naphthylphthalamic acid (NPA), IAA and GA3 respectively and also treated with NPA associated with IAA or GA3 respectively. The root length and curvature were measured after the primary root was placed horizontally for a period of time. The results indicated that at low concentrations both IAA (0.001 μmol·L-1) and GA3 (0.01-1 μmol·L-1) could facilitate the root elongation and gravitropic curvature and at high concentrations IAA (0.001-10 μmol·L-1) and GA3 (10-100 μmol·L-1) could restrain the root elongation and gravitropic curvature, that NPA could exert its inhibitions on the root elongation and gravitropic curvature as a whole, but at low concentrations NPA (0.4 μmol·L-1) tended to promote the root elongation, that at low concentrations both IAA and GA3 could oppose the prohibitive action of NPA on the root elongation and that the stimulative action of GA3 at low concentrations on the root elongation was independent of IAA.