CONTROL OF INTERNODE LENGTH IN PISUM-SATIVUM - FURTHER EVIDENCE FOR THE INVOLVEMENT OF INDOLE-3-ACETIC-ACID

The effects of altered endogenous indole-3-acetic (IAA) levels on elon gation in garden pea (Pisum sativum L.) plants were investigated. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 9-hydr oxyfluorene-9-carboxylic acid (HFCA) were applied to elongating intern odes of wild-type and mutant lkb plants. The lkb mutant was included b ecause elongating lkb internodes contained 2- to 3-fold less free IAA than those of the wild type. In the wild type, TIBA reduced both the I AA level and internode elongation below the site of application. Both TIBA and HFCA strongly promoted the elongation of lkb internodes and a lso raised IAA levels above the application site. The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) also markedly increased interno de elongation in lkb plants and virtually restored petioles and tendri ls to their wild-type length. In contrast, treatment of wildtype plant s with TIBA, HFCA, or 2,4-D caused little or no increase in elongation above the application site. The ethylene synthesis inhibitor aminoeth oxyvinylglycine also increased stem elongation in lkb plants, and comb ined application of HFCA and aminoethoxyvinylglycine restored lkb inte rnodes to the wild-type length. It is concluded that the level of IAA in wild-type internodes is necessary for normal elongation, and that t he reduced stature of lkb plants is at least partially attributable to a reduction in free IAA level in this mutant.