Journal Article

ABA Inhibits Embryo Cell Expansion and Early Cell Division Events During Coffee (<i>Coffea arabica</i> ‘Rubi’) Seed Germination

E. A. Amaral Da Silva, Peter E. Toorop, André A. M. Van Lammeren and Henk W. M. Hilhorst

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 102, issue 3, pages 425-433
Published in print September 2008 | ISSN: 0305-7364
Published online July 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn112
ABA Inhibits Embryo Cell Expansion and Early Cell Division Events During Coffee (Coffea arabica ‘Rubi’) Seed Germination

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Coffee seed germination represents an interplay between the embryo and the surrounding endosperm. A sequence of events in both parts of the seed determines whether germination will be successful or not. Following previous studies, the aim here was to further characterize the morphology of endosperm degradation and embryo growth with respect to morphology and cell cycle, and the influence of abscisic acid on these processes.

Methods

Growth of cells in a fixed region of the axis was quantified from light micrographs. Cell cycle events were measured by flow cytometry and by immunocytochemistry, using antibodies against β-tubulin. Aspects of the endosperm were visualized by light and scanning electron microscopy.

Key Results

The embryonic axis cells grew initially by isodiametric expansion. This event coincided with reorientation and increase in abundance of microtubules and with accumulation of β-tubulin. Radicle protrusion was characterized by a shift from isodiametric expansion to elongation of radicle cells and further accumulation of β-tubulin. Early cell division events started prior to radicle protrusion. Abscisic acid decreased the abundance of microtubules and inhibited the growth of the embryo cells, the reorganization of the microtubules, DNA replication in the embryonic axis, the formation of a protuberance and the completion of germination. The endosperm cap cells had smaller and thinner cell walls than the rest of the endosperm. Cells in the endosperm cap displayed compression followed by loss of cell integrity and the appearance of a protuberance prior to radicle protrusion.

Conclusions

Coffee seed germination is the result of isodiametric growth of the embryo followed by elongation, at the expense of integrity of endosperm cap cells. The cell cycle, including cell division, is initiated prior to radicle protrusion. ABA inhibits expansion of the embryo, and hence subsequent events, including germination.

Keywords: Abscisic acid; β-tubulin; Coffea arabica; coffee seed; cell morphology; germination; microtubules

Journal Article.  6156 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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