Morphogenesis of land plants and gravity-Mechanism of their resistance to gravity mediated by plant hormones-

Lignin formation in secondary cell walls is assumed to be essential for the evolution of land plants. Our microarray analysis of hypergravity-treated Arabidopsis inflorescence stems revealed that expression of genes involved in auxin signaling was modulated in response to hypergravity as well as those which are involved in lignin biosynthesis. Hypergravity treatment at 300g significantly increasedβ-glucuronidase activity in inflores-cence stems of DR5 :: GUS plants, indicating that endogenous auxin accumulation was enhanced by hypergravity treatment. The hypergravity-related increased expression levels of both DR5 :: GUS and lignin biosynthesis-related genes in inflorescence stems were suppressed after disbudding, indicating that the increased expression of lignin biosynthesis-related genes is dependent on an increase in auxin influx from the shoot apex.