Assignment Task: Brassinazole is a substance that inhibits the biosynthesis of brassinosteroids. You have two Arabidopsis mutants that you suspect do not produce brassinosteroids as they are both very small (pictured above), one is the dwf mutant the other the bri mutant, WT is a normal plant.
You allow seeds from dwf and bri to germinate on media supplemented with brassinosteroids.
You allow WT seeds to germinate on media supplemented with brassinazole and on normal media.
dwf plants growing on media supplemented with brassinosteroids grow like WT plants on normal media.
bri plants growing on media supplemented with brassinosteroids grow as WT on media supplemented with brassinazole.
A) Explain the results you observe. (Hint: brassinosteroid signaling), are your suspicions correct?
B) Observe the phenotypes of the mutant dwf and bri plants. Based on your observations, what would you say is the main function of brassinosteroids in plants?
Hormones in plants, unlike those in animals, have pleiotropic effects. This means that they are involved in the regulation of many different development processes. One such hormone is auxin.
C) Use your knowledge of the auxin signaling pathway and explain how auxin can regulate many different developmental processes in plants.
D) Auxin is one of many hormones that use the proteasome as a component of the signaling pathway. What is a proteasome and what is the advantage of including this mechanism in hormone signaling?