Journal Article

Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to <i>Geranium carolinianum</i>

N. S. Gama-Arachchige, J. M. Baskin, R. L. Geneve and C. C. Baskin

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 105, issue 6, pages 977-990
Published in print June 2010 | ISSN: 0305-7364
Published online April 2010 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcq078
Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to Geranium carolinianum

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  • Ecology and Conservation
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Background and Aims

Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum.

Methods

Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments.

Key Results

Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the ‘hinged valve’ (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. The morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium.

Conclusions

Dislodgment of swollen ‘hinged valve’ palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap (‘hinged valve gap’) differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.

Keywords: Erodium; Geraniaceae; Geranium; physical dormancy; seed-coat anatomy; seed burial; seed germination; water gap

Journal Article.  8422 words.  Illustrated.

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

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