1-Aminocyclopropane-1-carboxylic acid and abscisic acid during the germination of sugar beet (Beta vulgaris L.): a comparative study of fruits and seeds

Abstract

The control of sugar beet (Beta vulgaris L.) germination by plant hormones was studied by comparing fruits and seeds. Treatment of sugar beet fruits and seeds with gibberellins, brassinosteroids, auxins, cytokinins, and jasmonates or corresponding hormone biosynthesis inhibitors did not appreciably affect radicle emergence of fruits or seeds. By contrast, treatment with ethylene or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) promoted radicle emergence of fruits and seeds. Abscisic acid (ABA) acted as an antagonist of ethylene and inhibited radicle emergence of seeds, but not appreciably of fruits. High endogenous contents of ACC and of ABA were evident in seeds and pericarps of dry mature fruits, but declined early during imbibition. ABA-treatment of seeds and fruits induced seed ACC accumulation while ACC-treatment did not affect the seed ABA content. Transcripts of ACC oxidase (ACO, ethylene-forming enzyme) and ABA 8'-hydroxylase (CYP707A, ABA-degrading enzyme) accumulate in fruits and seeds upon imbibition. ABA and ACC and the pericarp did not affect the seed CYP707A transcript levels. By contrast, seed ACO transcript accumulation was promoted by ABA and by pericarp removal, but not by ACC. Quantification of the endogenous ABA and ACC contents, ABA and ACC leaching, and ethylene evolution, demonstrate that an embryo-mediated active ABA extrusion system is involved in keeping the endogenous seed ABA content low by 'active ABA leaching', while the pericarp restricts ACC leaching during imbibition. Sugar beet radicle emergence appears to be controlled by the pericarp, by ABA and ACC leaching, and by an ABA-ethylene antagonism that affects ACC biosynthesis and ACO gene expression.

Regulation of ethylene biosynthesis at the level of 1-aminocyclopropane-1-carboxylate oxidase (ACO) gene

“…As shown in pea seeds, ethylene may regulate its own biosynthesis through a positive feedback loop that enhances ACO expression (Petruzzelli et al 2000). Though, in contrast with pea seeds, no such autocatalytic enhancement was observed for ACO in germinating sugar beet (Hermann et al 2007), or the ACO2 orthologs of Sysimbrium officinale (Iglesias-Fernández and Matilla 2009) and Lepidium (Linkies et al 2009). The levels of ACO transcripts have been shown to be regulated not only by ethylene itself but also other phytohormones (Lin et al 2009).…”

“…Accumulation of ACOs and increased ethylene evolution accompany seed germination in several species (Munoz de Rueda et al 1995;Petruzzelli et al 2000;Hermann et al 2007;Linkies et al 2009;Iglesias-Fernández and Matilla 2010). In many instances it is ACO that controls the ethylene evolution during seed germination.…”

Ethylene Interacts with Abscisic Acid to Regulate Endosperm Rupture during Germination: A Comparative Approach UsingLepidium sativumandArabidopsis thaliana

“…Translation of ACO1 and ACO2 transcripts combined with mechanisms that regulate ACO protein stability could therefore explain the ACO activities in the radicle and endosperm cap of Lepidium seeds. In contrast with pea seeds, where a positive feedback loop involving ACO promotes ethylene biosynthesis (Petruzzelli et al, 2000), no such autocatalytic enhancement was evident for the ACO in germinating sugar beet (Beta vulgaris; Hermann et al, 2007) or the ACO2 orthologs of the Brassicaceae species Sisymbrium officinale (Iglesias-Fernandez and Matilla, 2009) and Lepidium (Figures 7 and 8). We found, however, that a basal level of ethylene signaling is required to maintain ACO2 transcript levels during germination.…”

“…Increased ethylene evolution and/or ACO accumulation is associated with the germination of many seeds (e.g., Leubner-Metzger et al, 1998;Petruzzelli et al, 2000;Chiwocha et al, 2005;Matilla et al, 2005;Hermann et al, 2007;Iglesias-Fernandez and Matilla, 2009). Ethylene evolution during seed germination is regulated by ACO, which catalyzes the final rate-limiting step in ethylene biosynthesis (Kucera et al, 2005;Matilla and Matilla-Vazquez, 2008).…”

Calcium Carbide-induced Changes in Germination, Morpho-phenological and Yield Traits in Cucumber (Cucumis sativus)

“…Germination starts with absorption of water, resulting in expansion and elongation of seed embryo and is completed when radicle protrudes from seed covering (Hermann et al, 2007). A large body of literature has been documented regarding the role of plant hormones and their interaction with various environmental factors on seed germination and seedling growth (Kucera et al, 2005;Müller et al, 2006;Hermann et al, 2007). Among various plant hormones, gibberellic acid and ethylene are well known regarding their role in breaking seed dormancy, while ABA is known to cause seed dormancy (Matilla and Matilla-Vazquez, 2008;Linkies et al, 2009).…”