Planta
Planta (1983) 159:289 299
9 Springer-Verlag 1983
The role of endogenous gibberellins in the formation of a-amylase by aleurone layers of germinating barley caryopses Rainer Atzorn and Elmar W. Weiler Lehrstuhl ffir Pflanzenphysiologie, Ruhr-Universit/it, Postfach 102148, D-4630 Bochum, Federal Republic of Germany
Abstract. Using sensitive and selective immunological assays we have shown that in germinating caryopses of Hordeum vulgare L. cv. Himalaya, the level of gibberellin A 4 (GA4) rises approximately 18- to 20-fold shortly ( 2 4 h) before 0~-amylase activity increases. Gibberellin A 4 is the predominant immunoreactive gibberellin during these developmental stages and reaches a peak amount of approximately 9 pmol per caryopsis about 48 h after imbibition. Isolated aleurone layers produce G A 4 in the presence of an exogenous gibberellin, such as GA1, which is not a biosynthetic precursor for GA 4 . Experiments with inhibitors of gibberellin biosynthesis indicate that gibberellin synthesis is required in this tissue for the induction of a-amylase. The inductive effect of exogenously applied GA 1 is indirect and appears to be mediated by GA 4. Embryos form predominantly GA1; however, very little of this material is released by isolated embryos into the incubation medium. The results presented make it unlikely that the role of the embryo in the process of 0~-amylase induction in aleurone layers is to provide gibberellins or gibberellin precursors. Key words: Aleurone layer co-Amylase - Ancymidol - Germination (barley) - Gibberellin and c~amylase - Gibberellin immunoassay - Hordeum (aleurone layer, gibberellin).
induce the formation of several hydrolytic enzymes, the most prominent being c~-amylase. This view is based upon the fact that the embryo is necessary for starch hydrolysis to occur in the endosperm (Haberlandt 1890) and that it can be replaced effectively by gibberellic acid (GA3; e.g. Paleg 1960). Gibberellin-like activity increases transiently in germinating barley caryopses, as a rule, but not under all conditions, several hours before the level of a-amylase increases (Groat and Briggs 1969). However, these experiments were always conducted with whole caryopses and thus, there exists no direct information as to whether the embryo is the source of GAs for the aleurone layer. In fact, isolated embryos failed to release physiologically active GAs rapidly enough to account for c~-amylase production in some experiments (Yomo and Iinuma 1967) but not in others (Radley 1967; Cohen and Paleg 1967). The nature of the endogenous GAs possibly involved is not clear. Most experiments indicated that GA 3 was predominant (Briggs 1973) while other workers found mainly GA 1 (Radley 1967). However, using a selective and sensitive immunological assay for GA3, no changes in the level of GA 3 in germinating caryopses of barley were detected (Weiler and Wieczorek 1981). The present study was carried out to obtain more detailed information on the nature, kinetics, tissue distribution and physiological significance of several GAs in germinating barley caryopses.
Introduction
It is generally assumed that in germinating barley gibberellins (GAs) produced by the embryo or the scutellum diffuse to the aleurone layer where they Abbreviations." ABA = abscisic acid; GA = gibberellin; GA 3 = gibberellic acid; RIA=radioimmunoassay; TLC=thin-layer chromatography
Material and methods Plant material. Hordeum vulgare L. cv. Himalaya, harvest 1978, grown locally in an isolated plot from material obtained in 1973 from the Washington State University, Pullman, USA, was used throughout. Compared with grain raised in Pullman (harvest 1980) which became available after the completion o f this study, the grain used here had a lower background amylase
290 level (
Planta (1983) 159:289 299
9 Springer-Verlag 1983
The role of endogenous gibberellins in the formation of a-amylase by aleurone layers of germinating barley caryopses Rainer Atzorn and Elmar W. Weiler Lehrstuhl ffir Pflanzenphysiologie, Ruhr-Universit/it, Postfach 102148, D-4630 Bochum, Federal Republic of Germany
Abstract. Using sensitive and selective immunological assays we have shown that in germinating caryopses of Hordeum vulgare L. cv. Himalaya, the level of gibberellin A 4 (GA4) rises approximately 18- to 20-fold shortly ( 2 4 h) before 0~-amylase activity increases. Gibberellin A 4 is the predominant immunoreactive gibberellin during these developmental stages and reaches a peak amount of approximately 9 pmol per caryopsis about 48 h after imbibition. Isolated aleurone layers produce G A 4 in the presence of an exogenous gibberellin, such as GA1, which is not a biosynthetic precursor for GA 4 . Experiments with inhibitors of gibberellin biosynthesis indicate that gibberellin synthesis is required in this tissue for the induction of a-amylase. The inductive effect of exogenously applied GA 1 is indirect and appears to be mediated by GA 4. Embryos form predominantly GA1; however, very little of this material is released by isolated embryos into the incubation medium. The results presented make it unlikely that the role of the embryo in the process of 0~-amylase induction in aleurone layers is to provide gibberellins or gibberellin precursors. Key words: Aleurone layer co-Amylase - Ancymidol - Germination (barley) - Gibberellin and c~amylase - Gibberellin immunoassay - Hordeum (aleurone layer, gibberellin).
induce the formation of several hydrolytic enzymes, the most prominent being c~-amylase. This view is based upon the fact that the embryo is necessary for starch hydrolysis to occur in the endosperm (Haberlandt 1890) and that it can be replaced effectively by gibberellic acid (GA3; e.g. Paleg 1960). Gibberellin-like activity increases transiently in germinating barley caryopses, as a rule, but not under all conditions, several hours before the level of a-amylase increases (Groat and Briggs 1969). However, these experiments were always conducted with whole caryopses and thus, there exists no direct information as to whether the embryo is the source of GAs for the aleurone layer. In fact, isolated embryos failed to release physiologically active GAs rapidly enough to account for c~-amylase production in some experiments (Yomo and Iinuma 1967) but not in others (Radley 1967; Cohen and Paleg 1967). The nature of the endogenous GAs possibly involved is not clear. Most experiments indicated that GA 3 was predominant (Briggs 1973) while other workers found mainly GA 1 (Radley 1967). However, using a selective and sensitive immunological assay for GA3, no changes in the level of GA 3 in germinating caryopses of barley were detected (Weiler and Wieczorek 1981). The present study was carried out to obtain more detailed information on the nature, kinetics, tissue distribution and physiological significance of several GAs in germinating barley caryopses.
Introduction
It is generally assumed that in germinating barley gibberellins (GAs) produced by the embryo or the scutellum diffuse to the aleurone layer where they Abbreviations." ABA = abscisic acid; GA = gibberellin; GA 3 = gibberellic acid; RIA=radioimmunoassay; TLC=thin-layer chromatography
Material and methods Plant material. Hordeum vulgare L. cv. Himalaya, harvest 1978, grown locally in an isolated plot from material obtained in 1973 from the Washington State University, Pullman, USA, was used throughout. Compared with grain raised in Pullman (harvest 1980) which became available after the completion o f this study, the grain used here had a lower background amylase
290 level (
