Effects of Light and Growth Regulators on Leaf Unrolling in Barley

Abstract

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.In etiolated grass seedlings the first leaf remains tightly rolled even when it penetrates the coleoptile; however, upon illumination this leaf unrolls rapidly. Leaf unrolling is caused by a greater growth of the cells of the upper mesophyll as compared to the remamiing mesophyll (2). Virgin (10) The present studies were undertaken in order to delineate the time course of events in the leaf unrolling process of barley as influenced by hormones and light. MATERIALS AND METHODSBarley seeds (Hordeum vulgare, L., var. Arivat) were soaked for 8 hr in aerated deionized water. The seeds were then placed between layers of cheesecloth on a stainless steel gauze supported by a 4-liter beaker containing 3.5 liters of aerated 2 mm CaSO4 solution (6). The seedlings were grown in darkness at 25 C for 6.5 days. All subsequent manipulations were carried out under a dim green safelight.Sections, 7 mm in length, were cut from the primary leaves starting 1 cm below the tip. In the leaf unrolling studies samples of 10 segments were floated on 10 ml of 0.001 M sodium acetate buffer, pH 5.5, containing the test chemicals, and incubated at 25 C. Stock solutions of the inhibitors were prepared in sodium acetate buffer. Stock solutions of GA and ABA were prepared by dissolving the compounds in 0.001 M sodium acetate and adjusting to pH 5.5 with 0.001 M acetic acid.Leaf width was determined by arranging segments, which had been blotted dry, on a glass plate fitted to an overhead projector. The enlarged image (X4) was projected onto a screen and measured. RESUlLTSWhen floated on buffer and illuminated, segments of the etiolated primary leaf of barley unroll and turn green. For the first 4 to 6 hr following illumination unrolling is slow; there is then a period of rapid expansion lasting approximately 6 hr followed by a period of less rapid unfolding (Fig. 1). Leaf unrolling is complete after about 24 hr. In contrast to the illuminated segments, those floated on buffer in the dark unroll much less. The small amount of unrolling tha...

Growth Inhibitors From Etiolated Leaves of Barley (Hordeum Vulgare L.)

“…DISCUSSION The experiments described have yielded evidence to support the hypothesis, put forward by Poulson and Beevers (1970), that the lag period prior to the rapid phase of leaf unrolling might involve a decrease in level of inhibitory compounds. They suggested ABA asa possible candidate but no ABA could be detected, either by paper chromatography and wheat coleoptile bioassay or by gas chromatography, in extracts from barley leaves.…”

“…wheat seed germination and barley leaf unrolling itself). Poulson and Beevers (1970) suggested that the lag phase of leaf unrolling following exposure to red light might involve the decline of an endogenous inhibitor, perhaps abscisic acid, in the leaves. An investigation was undertaken to test for the presence of an inhibitor of physiological importance in etiolated barley leaves and to see whether its activity decreased during the lag period of leaf unrolling.…”

Nucleic Acid Metabolism during Greening and Unrolling of Barley Leaf Segments

“…Arivat) were grown in darkness at 23 C as previously described (20). The 7-mm segUrbana, Illinois 61801 ments were excised, starting 1 cm below the tip, from the primary leaves of 6.5-day-old seedings.…”

“…Batches of 800 segments were frozen in liquid nitrogen and ground to a fine powder. The 20 min at 35 C, and then 0.1-ml samples were removed and precipitated with 5 ml of ice-cold 10% trichloroacetic acid containing 1% sodium pyrophosphate. The precipitates were subsequently transferred to nitrocellulose membrane filters (Schleicher and Schuell, Bac-T-Flex B6) and washed with 50 ml of cold 5% trichloroacetic acid.…”

“…The relative importance of the two processes during the early phases of photoinduced leaf development has not been established. The observation that unrolling (1,20) and greening (4,12) can be prevented by inhibitors of protein and RNA synthesis suggest that the increase in RNA and protein levels must accompany unrolling and greening.…”