Growth & geotropic curvature of Avena coleoptiles in presence of n-1-naphthylphthalamic acid

The fact that geotropic curvature is mediated by unequal rates of elongation on opposite sides of the bending structure has led to the general implication that depression of these growth rates should cause a corresponding inhibition of geotropic curvature. Recently published results have revealed that this expected relationship was not always observed when plants were treated with compounds such as 2,3,6trichlorobenzoic acid and n-1-naphthylphthalamic acid (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12). Selective inhibition of geotropic curvature bv n-1-naphthylphthalamic acid (NP) has been reported for a number of plants, including seedlings of corn, crucifer, cucumber, pea, lentil, sunflower, and tomato (3, 4, 5, 8). Since the data of Tsou Ching, Hamilton, and Bandurski (8) did not reveal a differential effect of NP on growth and geotropic curvature of intact Avena coleoptiles, the present study was undertaken to explore, in additional detail, the effects of NP on elongation and negative geotropism of isolated apical segments of Avena coleoptiles.