Journal of Experimental Botany 58: 3047-3060 (2007)

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

Katrin Hermann, Juliane Meinhard, Peter Dobrev, Ada Linkies, Bedrich Pesek, Barbara Heß, Ivana Machácková, Uwe Fischer, Gerhard Leubner-Metzger

Institute of Biology II, Botany / Plant Physiology, Albert-Ludwigs-University Freiburg, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany, Web: 'The Seed Biology Place' (K.H., A.L., B.H., G-L.-M.)
KWS SAAT AG, Grimsehlstr. 31, D-37555 Einbeck, Germany, Web: (J.M., U.F.)
Institute of Experimental Botany CAS, Rozvojová 263, CZ-16502 Prague 6, Czech Republic, Web: (P.D., B.P., I.M.)

Received June 15, 2007; accepted June 25, 2007

Beta vulgaris germination model

Figure 7. Working model for the interaction between abscisic acid (ABA), 1-aminocyclopropane-1-carboxylic acid (ACC, ethylene precursor), ethylene, and the pericarp on the germination response (radicle emergence) of Beta vulgaris (sugar beet) fruits.
According to this model the ABA content of the seed is kept low at ca. 1 pmol/seed in accordance with the non-dormant state. This is achieved by the combined action of ABA degradation, an 'embryo ABA level sensor' and an embryo-mediated active ABA extrusion system. The pericarp supports this system and allows fast ABA extrusion leading to the low seed ABA contents. In addition, even minor elevations in the seed ABA contents cause increased ACC biosynthesis and ACO transcript expression. In contrast to this, ACC does not affect the endogenous seed ABA contents. ACC can accumulate in the seed to extremely high contents and the pericarp restricts ACC leaching. Only a fixed amount of ca. 40 pmol/seed leached out irrespective of the endogenous ACC content. The pericarp restricts oxygen uptake and as the ACO enzyme requires oxygen, the conversion of ACC to ethylene is inhibited. In addition, the pericarp inhibits ACO gene expression, which might also be regulated by hypoxia. According to our model, sugar beet radicle emergence as the germination response depends on the antagonistic interaction between ACC/ethylene and ABA in the seed and on the physicochemical characteristics of the pericarp.

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   Abstract    Fig. 1               Fig. 2
Fig. 5               Fig. 6
Fig. 3               Fig. 4                Tab. 1
Fig. 7               Suppl. Fig. S1
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