Dormancy of the Barley Grain Is Correlated with Gibberellic Acid Responsiveness of the Isolated Aleurone Layer

Abstract

The relationship between barley grain dormancy and gibberellic acid (GA3) responsiveness of aleurone layers has been investigated. Barley (Hordeum distichum L. cvs Triumph and Kristina) grains were matured under defined conditions in a phytotron. Grains of Triumph plants grown under long-day/warm conditions had lower dormancy levels than grains of plants grown under short-day/cool conditions. Aleurone layers isolated from grains of long-day Triumph plants secreted more a-amylase and had a higher responsiveness to GA3 as measured by a-amylase secretion. Storage of the grains increased both the percentage of germination and the responsiveness of the aleurone to GA3. Use of different sterilization methods to break dormancy confirmed the correlation between germination percentage and aleurone layer GA3 responsiveness. The response of embryoless Triumph grains to GA3 was lower than that of the isolated aleurone layers, suggesting a role of the starchy endosperm in regulating the GA3 response of the aleurone layer. Grains of the cultivar Kristina harvested from short day-and long day-grown plants lacked dormancy, and their isolated aleurone layers had a similar responsiveness to GA3 as measured by aamylase secretion. The data indicate that the physiological state of the aleurone layers contributes to the percentage germination of the grains.During germination, the growing barley embryo synthesizes and secretes gibberellins into the starchy endosperm. Subsequently, the gibberellins diffuse into the aleurone to trigger the synthesis and secretion of hydrolytic enzymes. This classical view, reviewed in detail by Briggs (2), is based on the following observations. Isolated embryos synthesize gibberellins, whereas embryoless grains or isolated aleurone layers generally fail to synthesize hydrolytic enzymes. Addition of gibberellins or gibberellin-synthesizing embryos to half-grains or to aleurone layers induces a-amylase synthesis in a dose-dependent manner (2,3,13).Synthesis of gibberellins by isolated embryos, however, does not necessarily reflect the situation in whole grains. Radley (17) shows that an isolated scutellum synthesizes gibberellins, whereas a scutellum attached to the grain does not; synthesis of gibberellins in isolated embryos can be completely inhibited by low concentrations of sugars. Moreover, the studies on correlations between level of gibberellins

Integrated control of seed maturation and germination programs by activator and repressor functions of Viviparous-1 of maize.

“…This view is supported by our results showing that overexpression of VP1 in aleurone of germinating maize seeds was effective in repressing Amy-GUS (Table 2). A role of VP1 in maintaining seed dormancy is also consistent with the finding that dormancy in barley is correlated with a reduced GA inducibility of a-amylase genes in the aleurone (Schuurink et al 1992;Skadsen 1993). Hence, we suggest that VP1 plays a role in integrating the control of seed maturation, dormancy, and germination programs.…”

Gibberellin Requirement for Arabidopsis Seed Germination Is Determined Both by Testa Characteristics and Embryonic Abscisic Acid

“…The first one is the induction of the expression of genes encoding enzymes hydrolyzing the endosperm. This tissue confers part of the mechanical resistance to radicle protrusion, as demonstrated in tomato (Groot and Karssen, 1987;Groot et al, 1988), tobacco (LeubnerMetzger et al, 1996), and barley (Schuurink et al, 1992). The second mechanism consists of a direct stimulating effect on the growth potential of the embryo, as suggested for Arabidopsis (Karssen and Laçka, 1986).…”

Transcripts encoding an oleosin and a dormancy‐related protein are present in both the aleurone layer and the embryo of developing barley (Hordeum vulgare L.) seeds

“…In many plant species, seeds are dormant right after maturity and will not germinate when imbibed. In the aleurone layer, dormancy takes the form of unresponsiveness to GA-stimulation (Schuurink et a/., 1992). The pBS128 transcript from B. secalinus, which is maintained at a high level in dormant, but not in nondormant hydrated seeds, has been suggested to play a role in the maintenance of embryo dormancy (Goldmark et a/., 1992).…”