Brassinosteroid:: A modulator of the developmental window for salt-adaptation in Sorghum bicolor?

Leaf development of salt-treated Sorghum bicolor plants is influenced by treatment with 24-epibrassinolide (EBL), but only during a short period in development. This transient sensitivity coincides with a critical period of reorganization of regulations already identified in Sorghum, during which adaptation (through integration of effects of external perturbation in the new regulation network) is possible. By measuring, the effect of EBL on leaf malformations during their unfolding in plants exposed to 150 mM NaCl, it is shown that treatments with brassinosteroids (BR) enable modification of initiation, duration, and intensity of this critical period of reorganization. A critical period is characterized by modification of cell sensitivity to informative substances. Accordingly, it is suggested that BR, at specific concentrations and time in development, may induce changes in cellular sensitivity to many growth regulators. The parallels in the effects of EBL and NaCl Suggest that the transient inhibition in leaf elongation is not directly caused by the perturbation (addition of EBL or sublethal NaCl treatment). Rather, it results from interference between an exogenous perturbation and the structure of the regulation network.