AOBPreview published online on May 19, 2007
Annals of Botany, doi:10.1093/aob/mcm070
Morphology and Anatomy of Physical Dormancy in Ipomoea lacunosa: Identification of the Water Gap in Seeds of Convolvulaceae (Solanales)
1 Department of Biology, University of Kentucky, Lexington, KY 40506, USA
2 Department of Horticulture, University of Kentucky, Lexington, KY 40546, USA
3 Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546, USA
* For correspondence. E-mail: ccbask0{at}uky.edu
Received: 15 January 2007 Returned for revision: 13 February 2007 Accepted: 26 February 2007
Background and Aims: Convolvulaceae is the most advanced plant family (asterid clade) that produces seeds with physical dormancy (water-impermeable seed coat). There are several different opinions about the nature of the specialized structure (‘water gap’) in the seed coat through which water initially enters seeds of Convolvulaceae, but none of them has been documented clearly. The primary aim of the study was to identify the water gap in seeds of Ipomoea lacunosa (Convolvulaceae) and to describe its morphology, anatomy and function.
Methods: Light microscopy, scanning electron microscopy, tissue-sectioning, dye-tracking and blocking experiments were used to describe the morphology, anatomy and function of the water gap in seeds of I. lacunosa.
Key Results: Dormancy-breaking treatments caused slits to form around the two bulges on the seed coat adjacent to the hilum, and dye entered the seed only via the disrupted bulges. Bulge anatomy differs from that of the rest of the seed coat. Sclereid cells of the bulges are more compacted and elongated than those in the hilum pad and in the rest of the seed coat away from the bulges.
Conclusions: The transition area between elongated and square-shaped sclereid cells is the place where the water gap opens. Morphology/anatomy of the water gap in Convolvulaceae differs from that of taxa in the other 11 angiosperm plant families that produce seeds with physical dormancy for which it has been described.
Key words: Convolvulaceae, Ipomoea, seed coat anatomy, seed dormancy, seed germination, palisade layer, physical dormancy, water gap, water-impermeable seed coat
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