Blockage of Brassinosteroid Biosynthesis and Sensitivity Causes Dwarfism in Garden Pea

Abstract

Endogenous brassinosteroids (BRs) in the dwarf mutants lka and lkb 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 lkb 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 lkb seedlings. These findings indicate that the lkb 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 lka plants contained only 50% less brassinolide and 5 times more castasterone than the equivalent wild-type tissues. The lka seedlings were approximately 100 times less responsive to brassinolide than the lkb mutant, and application of castasterone had only a marginal effect on lka internode growth, suggesting that the lka lesion results in impaired sensitivity to BR.