The effects of temperature and IAA concentration on the latent period for IAA-induced rapid growth of Avena coleoptile segments.

Indoleacetic acid buffered at pH 7.0 induces a high growth rate in Avena coleoptile segments after a latent period, the duration of which is dependent upon both IAA concentration and temperature. A minimum latent period of 7.3 min is observed at 25° C with 10(-3) M IAA in phosphate buffer at pH 7.0.In contrast, 5×10(-3) M IAA made up in 0.01 M KH2PO4 alone, promotes elongation almost immediately, regardless of whether the segments have been previously incubated in 0.01 M KH2PO4 at pH 4.7, or phosphate buffer at pH 7.0. This immediate response is unaffected by 10(-4) M KCN which abolishes the rapid growth induced by 5×10(-3) M IAA buffered at pH 7.0 but does not affect the immediate appearance of low-pH-induced growth. Since we consistently find solutions of 5×10(-3) M IAA in 0.01 M KH2PO4 to have a pH of 3.5, our results indicate that the immediate growth response elicited by this solution is attributable to its low pH rather than to the presence of IAA as previously reported in the literature.