Blockage of brassinosteroid biosynthesis and sensitivity causes dwarfism in garden pea

Endogenous brassinosteroids (BRs) in the dwarf mutants Ika and Ikb of garden pea (Pisum sativum L.) and comparable wild-type plants were quantified by gas chromatography-selected ion monitoring using deuterated internal standards. In young shoots of the Ikb mutant, the levels of brassinolide, castasterone, and 6-deoxocastasterone were 23-, 22-, and 9-fold lower, respectively, than those of wild-type plants. Applications of brassinolide, castasterone, typhasterol, 3-dehydroteasterone, and teasterone normalized internode growth of Ikb seedlings. These findings indicate that the Ikb plants are BR-deficient mutants, probably as a consequence of a block in the BR biosynthetic pathway prior to the production of teasterone. Young shoots of Ika plants contained only 50% less brassinolide and 5 times more castasterone than the equivalent wild-type tissues. The Ika seedlings were approximately 100 times less responsive to brassinolide than the Ikb mutant, and application of castasterone had only a marginal effect on Ika internode growth, suggesting that the Ika lesion results in impaired sensitivity to BR.