Cell-wall structure and chemical components in the root endodermis and exodermis of cereal roots as an environmental response and their functional meanings.

研究了谷类作物根部对干旱、渍水和盐分的解剖响应。干旱条件下，水稻根系表现为根内皮层细胞壁增厚，特别是耐旱旱稻品种。此外，耐旱性强的旱稻品种加厚的细胞壁中硅的含量高于旱稻品种。另一方面，所有水稻品种在淹水条件下内胚层细胞壁的增厚都是有限的。在旱地作物小麦中，淹水条件下根内胚层的细胞壁厚度与旱作条件下相似或更大。此外，在水淹条件下，以氨为氮源的生长介质促进了小麦和玉米内胚层细胞壁的增厚和木质化。旱地谷类作物内胚层细胞壁的增厚和木质化的增强，可能有助于减少还原土壤中有害成分向根中央组织的渗透。盐分胁迫降低了水稻种子根中Casparian带形成位置与根尖的距离。为了弄清胁迫是否真的加速了Casparian带的形成，开发了一种新的水稻育苗实验系统，即只用甘露醇引起的高渗透压处理一侧种子根。用这种方法生长的种子根的横切面与同龄的处理侧和对照侧相同。切片观察表明，较高的渗透压不会加速Casparian带的形成，但会加速Suberin片层的增厚。

Anatomical response of roots to drought, water-logging and salinity in the root of cereal crops was investigated. Rice roots exhibited cell wall thickening of root endodermis in drought, in particular in drought-tolerant upland rice varieties. Besides, the drought-tolerant upland rice varieties had higher content of silicon in the thickened cell walls than the lowland rice variety. On the other hand, the thickening of endodermal cell wall was limited in all the rice varieties under flooded conditions. In wheat, an upland crop, the cell wall of root endodermis showed similar or rather larger thickness under flooded condition than in aerobic condition. Moreover, presence of ammonium as the nitrogen source in the growth medium enhanced the cell wall thickening and lignification of endodermal cell wall under flooded condition in wheat and maize. Those enhancement of thickening and lignification of endodermal cell wall in upland cereal crops may contribute to decline the infiltration of harmful components in reduced soil into the central tissues of roots. Salinity stress decreased the distance of the position of Casparian band formation from the root apex in rice seminal roots. To clarify if the onset of Casparian band formation is really accelerated by the stress, a new experimental system to grow rice seedlings with treating only one side of the seminal root with high osmotic pressure caused by mannitol was developed. A cross section of the seminal roots grown with this method had treated side and control side with the same age. The observation of the cross sections suggested that the Casparian band formation was not hastened but the thickening of the suberin lamellae was accelerated by the higher osmotic pressure.