AOBPreview originally published online on July 15, 2006
Annals of Botany 2006 98(3):545-553; doi:10.1093/aob/mcl145
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Water Uptake by Dry Beans Observed by Micro-magnetic Resonance Imaging
1 National Institute of Vegetable and Tea Science, Ano, Mie 514-2392, Japan, 2 National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan and 3 Oak-Hill Georgic Patch-Work Laboratory, 4-13-10 Miyamoto, Funabashi, Chiba 273-0003, Japan
* For correspondence. E-mail mkoizumi{at}affrc.go.jp
Received: 9 March 2006 Returned for revision: 28 April 2006 Accepted: 25 May 2006 Published electronically: 15 July 2006
• Background and Aims Water uptake by dry kidney beans (Phaseolus vulgaris ‘Rajma’) and adzuki beans (Vigna angularis) was traced using micro-magnetic resonance imaging in order to elucidate the channel of water entry, the manner of water delivery and the timing of swelling of the seeds.
• Methods Magnetic resonance images of beans absorbing water were continuously measured with the single-point imaging method for 16 h or 20 h at 15-min intervals. With this technique, it was possible to detect and visualize the location of water in the beans, at a low water content, in the initial stages of water entry.
• Key Results Water was taken up through a specified tissue, the lens, near the hilum, and distributed primarily to the testa. When water reached the radicle, it began to be incorporated into cotyledons with considerable swelling of the seeds. Water uptake took place within a short time for kidney beans. The initial process of water entry was associated with mechanical vibration of the seed. Rapid hydration of the testa and the swelling of the cotyledons were then observed. Water was supplied to cotyledons through the adaxial epidermis. In contrast, it took a long time, approx. 7 h, to activate the water channel of the lens for adzuki beans which have a tightly fitting testa. Steeping of the testa was not uniform, which induced temporary slanting before enlargement of the seed.
• Conclusions The activation of the lens as the sole water channel, the delivery of water to the radicle within the testa, the swelling of the cotyledons, and the further increment of water are physiologically different processes during imbibition, and were separated by locating water in various tissues and by analysing the time course of water uptake using magnetic resonance imaging with the single-point imaging method.
Key words: Water uptake, dry beans, the role of testa, lens, real-time imaging, MRI, Phaseolus vulgaris, Vigna angularis
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