The bushy pea mutant is IAA-deficient

The bushy mutant of pea (Pisum sativum L.) is characterized by short, thin stems, very small leaves and profuse branching. The bushy phenotype is conferred by a dominant allele, termed bsh. Here we show that bushy plants contain lower levels of free indole-3-acetic acid (IAA) than wild-type (WT) plants. On emergence from the growth medium, bushy seedlings do not immediately display the mutant phenotype, and the effect of bsh on IAA content is small. After 10-14 days, the bushy phenotype begins to develop, and while the IAA content rises in WT plants, it falls in the mutant. The resulting difference in IAA level between WT and mutant can be up to 12-fold. Although there is a deficiency of free IAA in bushy plants, the total IAA content (including free and conjugated forms) was not reduced in comparison with the WT. Furthermore, in bushy plants, the level of the main IAA conjugate in pea, IAAsp, was not reduced to the same extent as that of IAA, and metabolism studies indicated that faster IAA deactivation might contribute to IAA deficiency in the mutant. Application of IAA to bushy plants did not result in a WT phenocopy. However, the short internodes and profuse branching of bushy plants is consistent with classical views on how IAA affects plant development.