Gibberellins, brassinosteroids and light-regulated development

The regulation of plant development by light requires the action of several well-studied plant hormones. However, the mechanism by which light and hormones affect identical developmental responses remains unclear. Recently, studies of mutants altered in light signal perception or transduction have suggested a role for gibberellins and brassinosteroids in light-regulated development. For instance, mutants in the major light-stable phytochrome from several plant species exhibit altered responsiveness to, or metabolism of, gibberellins. In contrast, mutants that develop as light-grown plants in the absence of light have implicated a role for brassinosteroids in the control of cell elongation, the expression of photoregulated genes, and the promotion of apical dominance, leaf senescence and male fertility. Future studies should help elucidate whether light and hormones independently affect these developmental responses or whether hormones are involved in the sequence of events initiated by excitation of photoreceptors.