Root Cortex Provides a Venue for Gas-Space Formation and Is Essential for Plant Adaptation to Waterlogging
Root Cortex Provides a Venue for Gas-Space Formation and Is Essential for Plant Adaptation to Waterlogging
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DOI：
10.3389/fpls.2019.00259
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发表时间：
2019-03-29
影响因子：
5.6
通讯作者：
Nakazono, Mikio
中科院分区：
文献类型：
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作者：
Yamauchi, Takaki;Abe, Fumitaka;Nakazono, Mikio
溶生通气组织是淹水土壤中植物根系皮层细胞死亡和溶解而形成的通气组织，是植物体内氧从地上部向根尖长距离运输的关键。虽然许多研究集中在根中通气组织的数量，通气组织形成的根皮层的大小的意义受到较少的研究关注。在本研究中，我们评估了高地作物，小麦（Triticum aestivum）和玉米（Zea mays ssp.）mays）和湿地作物水稻（Oryza sativa）在通气或停滞缺氧条件下的生长;后者可以模拟淹水土壤中气体成分的变化。分析表明，在滞水条件下，三种植物的全根和皮层面积均增加。水稻根的皮层与中柱的比值（CSR）和通气组织与皮层的比值（ACR）与气室的面积有关，均远高于小麦和玉米根，这表明这些解剖特征对根沿着的高氧运输能力是必不可少的。为了验证这一假设，径向氧损失（ROL），这是从根内到外部介质中的氧扩散通量，从厚和薄的不定根的水稻使用圆柱形（根套）的氧电极测量，植物的芽在空气中和根在无氧介质中。正如预期的那样，具有较大皮层和通气组织面积的粗根的ROL率高于细根。ROL率最高的是在水稻根的顶端部分，几乎没有检测到通气组织，但在皮层立方细胞排列提供组织孔隙。我们的结论是，高CSR结合大根直径是一个功能，促进氧气运输从地上部基地的植物根尖。此外，我们建议，CSR应该是一个有用的定量指标，评价和改良的根系性状有助于作物耐涝。
Lysigenous aerenchyma, which develops by death and subsequent lysis of the cortical cells in roots, is essential for internal long-distance oxygen transport from shoot base to root tips of plants in waterlogged soil. Although many studies focus on the amounts of aerenchyma in roots, significance of the size of the root cortex in which aerenchyma forms has received less research attention. In the present study, we evaluated the cross-sectional area of each root tissue in adventitious roots of upland crops, wheat (Triticum aestivum) and maize (Zea mays ssp. mays), and the wetland crop, rice (Oryza sativa) under aerated or stagnant deoxygenated conditions; the latter can mimic the changes in gas composition in waterlogged soils. Our analyses revealed that the areas of whole root and cortex of the three species increased under stagnant conditions. In rice roots, cortex to stele ratio (CSR) and aerenchyma to cortex ratio (ACR), which is associated with the areas of gas spaces, were much higher than those in wheat and maize roots, suggesting that these anatomical features are essential for a high capacity for oxygen transport along roots. To test this hypothesis, rates of radial oxygen loss (ROL), which is the diffusive flux of oxygen from within a root to the external medium, from thick and thin adventitious roots of rice were measured using a cylindrical (root-sleeving) oxygen electrode, for plants with shoots in air and roots in an oxygen-free medium. As expected, the rate of ROL from thick roots, which have larger cortex and aerenchyma areas, was higher than that of thin roots. The rate of ROL was highest at the apical part of rice roots, where aerenchyma was hardly detected, but at which cuboidal cell arrangement in the cortex provides tissue porosity. We conclude that high CSR in combination with large root diameter is a feature which promotes oxygen transport from shoot base to root tips of plants. Moreover, we propose that CSR should be a useful quantitative index for the evaluation and improvement of root traits contributing to tolerance of crops to soil waterlogging.