Effects of Light and Growth Regulators on Leaf Unrolling in Barley

The influence of light, gibberellic acid, and abscisic acid on unrolling of etiolated barley leaf segments was investigated. Gibberellic acid stimulated unrolling of both illuminated and nonilluminated leaf segments. In contrast, abscisic acid prevented light-stimulated unrolling and abolished the slight unrolling of segments maintained in the dark.Analysis of the time course of photoinduced unrolling showed a lag period of 6 hours before the onset of rapid leaf unrolling. The application of gibberellic acid to illuminated segments shortened this lag phase. Also, incubating the segments in buffer in darkness prior to illumination eliminated the lag period. Inhibitors of RNA and protein synthesis prevented light- and gibberellic acid induced unrolling, indicating a requirement for macromolecular synthesis. The possibilities that the lag period of unrolling following illumination represents the time required for the removal of endogeneous inhibitor or the synthesis of essential macromolecules are discussed.