School of Biology and Environmental Science, Science Centre West, University College Dublin, Belfield, Dublin 4, Ireland.
J Exp Bot. 2011 Jan;62(2):717-33. doi: 10.1093/jxb/erq312. Epub 2010 Oct 25.
Prior to an assessment of the role of aquaporins in root water uptake, the main path of water movement in different types of root and driving forces during day and night need to be known. In the present study on hydroponically grown barley (Hordeum vulgare L.) the two main root types of 14- to 17-d-old plants were analysed for hydraulic conductivity in dependence of the main driving force (hydrostatic, osmotic). Seminal roots contributed 92% and adventitious roots 8% to plant water uptake. The lower contribution of adventitious compared with seminal roots was associated with a smaller surface area and number of roots per plant and a lower axial hydraulic conductance, and occurred despite a less-developed endodermis. The radial hydraulic conductivity of the two types of root was similar and depended little on the prevailing driving force, suggesting that water uptake occurred along a pathway that involved crossing of membrane(s). Exudation experiments showed that osmotic forces were sufficient to support night-time transpiration, yet transpiration experiments and cuticle permeance data questioned the significance of osmotic forces. During the day, 90% of water uptake was driven by a tension of about -0.15 MPa.
在评估水通道蛋白在根系吸水过程中的作用之前，需要了解不同类型根系中水分移动的主要途径和昼夜期间的驱动力。本研究以水培生长的大麦（Hordeum vulgare L.）为材料，分析了 14-17 天龄植株的两种主要根系类型的水力传导率与主要驱动力（静水压力、渗透压）的关系。胚根对植物水分吸收的贡献为 92%，不定根为 8%。与胚根相比，不定根的贡献较低，这与根的表面积和数量较小以及轴向水力传导率较低有关，尽管不定根的内皮层发育较差。两种类型根系的径向水力传导率相似，受流行驱动力的影响很小，这表明水分吸收是沿着涉及跨膜的途径进行的。渗出实验表明，渗透压足以支持夜间蒸腾，但蒸腾实验和角质层渗透率数据质疑渗透压的重要性。白天，约 90%的水分吸收是由约 -0.15 MPa 的张力驱动的。
