United States Department of Agriculture-Agricultural Research Service, Beckley, West Virginia 25802.
Plant Physiol. 1992 Mar;98(3):901-7. doi: 10.1104/pp.98.3.901.
The O(2) permeability of legume root nodules is under physiological control; decreases in permeability are triggered by various forms of stress. Two linked mathematical models were used to explore several hypotheses concerning the physical nature of the variable diffusion barrier in nodules. Respiration and diffusion of dissolved O(2) and oxygenated leghemoglobin were simulated for the nodule cortex and the nodule interior. Measured nodule permeabilities were shown to be inconsistent with the hypothesis that large numbers of air-filled pores penetrate the diffusion barrier. Changes in the affinity of leghemoglobin for O(2) or in the rate of cytoplasmic streaming in diffusion barrier cells did not result in the large changes in O(2) permeability reported for real nodules. The presence or absence, but not the thickness, of aqueous plugs in radial pores through the cortex was found to have a large effect on permeability. Flooding of intercellular spaces, either between layers of cells in the cortex or in the nodule interior, also caused large changes in simulated permeability. The unsteady-state O(2) method for determining nodule permeability was tested using data generated by the model. The accuracy of the method was confirmed, provided that certain assumptions (full oxygenation of leghemoglobin under pure O(2) and uniform conditions in the nodule interior) are met.
豆科植物根瘤的 O2 通透性受生理控制；通透性的降低是由各种形式的胁迫触发的。使用两个关联的数学模型来探索关于可变扩散屏障物理性质的几个假设。模拟了溶解氧和氧合豆血红蛋白在根瘤皮层和根瘤内部的呼吸和扩散。测量的根瘤通透性与假设不一致，即大量充满空气的孔穿透扩散屏障。豆血红蛋白对 O2 的亲和力或扩散屏障细胞中细胞质流动的速率的变化并没有导致实际根瘤报告的 O2 通透性的大变化。发现径向皮层孔中水性塞的存在与否（而不是厚度）对通透性有很大影响。细胞间空间的淹没，无论是在皮层的细胞层之间还是在根瘤内部，也会导致模拟通透性的大变化。使用模型生成的数据测试了用于确定根瘤通透性的非稳态 O2 方法。只要满足某些假设（纯 O2 下豆血红蛋白的完全氧合和根瘤内部的均匀条件），该方法的准确性就得到了确认。
