Abstract
We studied the organ-specificity of BR biosynthesis in Arabidopsis, using two different approaches: we analyzed the expression of BR-related genes using real-time quantitative RT-PCR, and analyzed endogenous BRs using gas chromatography-mass spectrometry. Endogenous BRs and the expression of BR-related genes were detected in all organs tested. The highest level of endogenous BRs and the highest expression of the BR6ox1, the BR6ox2, and the DWF4 genes were observed in apical shoots, which contain actively developing tissues. These genes are important in BR biosynthesis, since they encode the rate-limiting or farthest downstream enzyme in the BR biosynthesis pathway. The second highest level of endogenous BRs and expression of BR6ox1 and DWF4 were observed in siliques, which contains actively developing embryos and seeds. These findings indicate that BRs are synthesized in all organs tested, but are most actively synthesized in young actively developing organs. In contrast, synthesis was limited in mature organs.
