Brassinosteroids (BRs) are a group of naturally occurring plant steroids with structural similarities to insect and animal steroid hormones. Exogenous application of BRs to plant

plant steroids with structural similarities to insect and animal steroid hormones. Exogenous application of BRs to plant tissues at nanomolar to micromolar concentrations evokes cell elongation, proliferation, differentiation, and organ bending and also affects a number of other physiological processes. Recent molecular genetic studies of BR action have revealed that these compounds regulate gene expression and are essential for normal plant growth and development. However, to understand the mechanism by which BRs regulate the growth and development of plants, it is necessary to identify proteins regulated by BR. Lamina inclination, which resembles the epinasty phenomenon caused by ethylene, is the result of the greater cell expansion of adaxial cells relative to the adorsal cells in the joint region. A change in cell wall extensibility or loosening is necessary for cell expansion. Xyloglucan endotransglycosylase, a cell wall-loosening enzyme, has been shown to be up-regulated by brassinolide (BL) in rice (Oryza sativa L.). Although the molecular basis for cell wall modifications is in large part unknown, it is possible that BL and its induced ethylene might work in sequence or together, resulting in lamina inclination. In addition, treatment with nanomolar or micromolar concentrations of BL, respectively, promotes or inhibits the growth of rice roots. However, there is still little information about proteins induced by BRs in rice plants. High-resolution two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is very useful for separating complex protein mixtures, and sequence analysis of protein separated by 2D-PAGE became possible with the gas-phase protein sequencer. Computer-aided image analysis and 2DPAGE have contributed to the development of the rice protein database. The techniques of proteome analysis have been employed to study alterations in rice cellular protein expression in response to various stimuli or as a result of differentiation and development. The study of partial amino acid sequence analysis of plant proteins will contribute greatly to the field of molecular biology for the identification of proteins through homology search. The information thus obtained from amino acid sequencing of these proteins will be helpful in predicting the function of the proteins and for molecular cloning in future experiments. Moreover, knowing which proteins are being synthesized in rice seedlings under a variety of physiological conditions can lead to identifying the roles of those proteins. Furthermore, 2D-PAGE separation and analysis provide a convenient way to study the various proteins that are present or induced in rice seedlings under different growth conditions, both normal and under stress. In this study, we investigated the rice lamina joint and root proteins induced by treatment with BL using proteome analysis techniques. The effects of BL concentration on intact lamina inclination and root growth in rice were examined and the N-terminal amino acid sequences of proteins increased and decreased by BL treatment were determined. The function of these proteins and the relationship between BL and ethylene after the amino acid sequences determined here were compared with those of known proteins.