Identification of Brassinosteroids That Appear to Be Derived from Campesterol and Cholesterol in Tomato Shoots

Abstract

Brassinosteroids (BRs) are steroidal plant hormones that are widely distributed in higher plants. When applied exogenously, BRs have various physiological effects on the growth and development of plants (Sakurai and Fujioka 1993). The activities of BRs can be distinguished from those of other plant hormones, such as auxins and gibberellins (Sasse 1990, Yokota 1997). The essential roles of BRs in many aspects of plant growth, in particular cell elongation, have been demonstrated by the discovery of BRdeficient dwarf mutants of Arabidopsis thaliana, namely, det2 (Li et al. 1996), cpd/cbb3 (Szekeres et al. 1996, Kauschmann et al. 1996) and dim/cbbl (Takahashi et al. 1995, Kauschmann et al. 1996), and of Pisum sativum, namely, Ikb (Nomura et al. 1997) and Ik (Yokota et al. unpublished). These findings were supported by the identification of BR-insensitive mutants of A. thaliana, namely, bril/cbb2 (Clouse et al. 1996, Kauschmann et al. 1996) and of P. sativum, namely, Ika (Nomura et al. 1997). Tomato (Lycopersicon esculentum) is an important crop plant with well-studied genetic background and a number of tomato mutants with various growth characteristics that include dwarfism have been isolated (Karssen et al. 1987, Reid