Water Movement Through Root Systems
Water Movement Through Root Systems
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通过根系的水分运动
DOI：
10.1098/rstb.1976.0025
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
E. Newman
中科院分区：
文献类型：
--
作者：
E. Newman
根系对水流有相当大的阻力。这种抗性很重要，因为它会影响植物地上部分的水分不足，即使根系在潮湿的土壤中，水分不足也会增加。单位表面积根系的渗透性因种而异，也因同一根的不同部位而异（取决于树龄）。它对温度、氧气和盐度等环境条件很敏感；这表明阻力的主要部分存在于“径向流动途径”中的生物物质中，即根表面和进入木质部之间。哪一条是径向流动的主要途径是不确定的。可能的替代途径有：(1)液泡途径，从一个液泡传递到另一个液泡，穿过皮层和其他组织；(2)自由空间/内胚层通路，水在细胞壁内移动，但在内胚层处进入原生质；或(3)同质途径，水在原生质中移动，并通过胞间连丝从一个细胞传递到另一个细胞。本文以已知细胞尺寸和根通透性的玉米初生根为基础，进行了计算，以显示膜、壁材料和胞间连丝的通透性对三种途径中的每一种都是必要的。这些计算预测了最可能的途径是同质。由于细胞壁材料的渗透性太低，自由空间/内皮层通路不太可能。一些实验证据也支持同质途径。在木质部纵向流动中，根的渗透性在种间有很大的差异。通常这种木质部流动将呈现比径向流动途径小得多的阻力。然而，没有足够的证据表明，在水压力下，容器内的气泡是否会大大增加阻力。
The root system provides a considerable resistance to water flow through it. This resistance is important because it influences the water deficits which can build up in the above-ground parts of the plant even when the roots are in moist soil. The permeability of roots per unit surface area varies between species, and between different parts of the same root (depending on age). It is sensitive to environmental conditions such as temperature, oxygen and salinity; this suggests that a major part of the resistance lies in living material in the 'radial-flow pathway', i.e. between the root surface and entry to the xylem. It is uncertain which is the main pathway of radial flow. Possible alternatives are: (1) the vacuolar pathway, crossing the cortex and other tissues by passing from vacuole to vacuole; (2) the free-space/endodermis pathway, water moving in the cell walls except at the endodermis where it enters the protoplasm; or (3) the symplasm pathway, water moving in the protoplasm and passing from cell to cell by plasmodesmata. Calculations are presented, based on the primary root of maize whose cell dimensions and root permeability are known, to show what permeabilities of membranes, wall material and plasmodesmata would be necessary to allow each of the three pathways to predominate. These calculations predict the symplasm as the most likely pathway. The free-space/endodermis pathway is unlikely because the permeability of cell wall material is too low. Several pieces of experimental evidence also favour the symplasm pathway. There are large variations between species in the permeability of roots for longitudinal flow in the xylem. Usually this xylem flow will present much less resistance than the radial flow pathway. However, there is no adequate evidence on whether the resistance may be greatly increased by bubble formation in vessels under water stress.