Koizumi Mika, Kikuchi Kaori, Isobe Seiichiro, Ishida Nobuaki, Naito Shigehiro, Kano Hiromi
National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan.
Ann Bot. 2008 Sep;102(3):343-52. doi: 10.1093/aob/mcn095. Epub 2008 Jun 19.
Imbibition of Japanese soybean (Glycine max) cultivars was studied using micro-magnetic resonance imaging (MRI) in order to elucidate the mechanism of soaking injury and the protective role of the seed coat.
Time-lapse images during water uptake were acquired by the single-point imaging (SPI) method at 15-min intervals, for 20 h in the dry seed with seed coat, and for 2 h in seeds with the seed coat removed. The technique visualized water migration within the testa and demonstrated the distortion associated with cotyledon swelling during the very early stages of water uptake.
Water soon appeared in the testa and went around the dorsal surface of the seed from near the raphe, then migrated to the hilum region. An obvious protrusion was noted when water reached the hypocotyl and the radicle, followed by swelling of the cotyledons. A convex area was observed around the raphe with the enlargement of the seed. Water was always incorporated into the cotyledons from the abaxial surfaces, leading to swelling and generating a large air space between the adaxial surfaces. Water uptake greatly slowed, and the internal structures, veins and oil-accumulating tissues in the cotyledons developed after the seed stopped expanding. When the testa was removed from the dry seeds before imbibition, the cotyledons were severely damaged within 1.5 h of water uptake.
The activation of the water channel seemed unnecessary for water entry into soybean seeds, and the testa rapidly swelled with steeping in water. However, the testa did not regulate the water incorporation in itself, but rather the rate at which water encountered the hypocotyl, the radicle, and the cotyledons through the inner layer of the seed coat, and thus prevented the destruction of the seed tissues at the beginning of imbibition.
利用微观磁共振成像（MRI）研究日本大豆（Glycine max）品种的吸胀过程，以阐明浸泡损伤的机制以及种皮的保护作用。
通过单点成像（SPI）方法，每隔15分钟获取吸水过程中的延时图像，带种皮的干种子吸水20小时，去除种皮的种子吸水2小时。该技术可视化了种皮内的水分迁移，并展示了吸水早期子叶肿胀相关的变形。
水分很快出现在种皮中，并从靠近种脊处绕过种子的背面，然后迁移到种脐区域。当水分到达下胚轴和胚根时，会出现明显的突出，随后子叶肿胀。随着种子增大，在种脊周围观察到一个凸起区域。水分总是从子叶的远轴面进入，导致肿胀，并在近轴面之间产生一个大的气腔。种子停止膨胀后，吸水速度大大减慢，子叶中的内部结构、叶脉和油脂积累组织开始发育。在吸胀前从干种子上去除种皮，子叶在吸水1.5小时内就会受到严重损伤。
水分进入大豆种子似乎不需要水通道的激活，种皮在水中浸泡时会迅速膨胀。然而，种皮本身并不调节水分的进入，而是调节水分通过种皮内层接触下胚轴、胚根和子叶的速度，从而在吸胀开始时防止种子组织被破坏。
