PHYSIOLOGICAL AND MOLECULAR EFFECTS OF BRASSINOSTEROIDS ON ARABIDOPSIS-THALIANA

We examined the effects of brassinosteroids on Arabidopsis thaliana (L .) Henyh. ecotype Columbia in order to develop a model system for stud ying gene regulation by plant steroids. Submicromolar concentrations o f two brassinosteroids, brassinolide and 24-epibrassinolide, stimulate d elongation of Arabidopsis peduncles and inhibited root elongation, r espectively. Furthermore, brassinolide altered the abundance of specif ic in vitro translatable mRNAs from peduncles and whole plants of Arab idopsis. Root elongation in the auxin-insensitive Arabidopsis mutant a xr1 was inhibited by 24-epibrassinolide but not by 2,4-D, indicating a n independent mode of action for these growth regulators in this physi ological response.