The Role of Brassinosteroids in Shoot Gravitropism

In the current model of gravitropism, negative gravitropic (upward) growth of the shoot of a dicotyledonous plant involves sedimentation of starch-containing plastids (statoliths) in the endodermis (starch sheath). Here we show that high levels of brassinosteroids (BRs) counteract gravitropic growth, while BR deficiency enhances gravitropism irrespective of the presence of a functional starch sheath. These data support a role for BRs as negative regulators of the shoot graviresponse.