Vanhees Dorien J, Schneider Hannah M, Sidhu Jagdeep Singh, Loades Kenneth W, Bengough A Glyn, Bennett Malcolm J, Pandey Bipin K, Brown Kathleen M, Mooney Sacha J, Lynch Jonathan P
School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire, UK.
The James Hutton Institute, Invergowrie, UK.
Plant Cell Environ. 2022 Mar;45(3):789-804. doi: 10.1111/pce.14175. Epub 2021 Sep 7.
Radial expansion is a classic response of roots to a mechanical impedance that has generally been assumed to aid penetration. We analysed the response of maize nodal roots to impedance to test the hypothesis that radial expansion is not related to the ability of roots to cross a compacted soil layer. Genotypes varied in their ability to cross the compacted layer, and those with a steeper approach to the compacted layer or less radial expansion in the compacted layer were more likely to cross the layer and achieve greater depth. Root radial expansion was due to cortical cell size expansion, while cortical cell file number remained constant. Genotypes and nodal root classes that exhibited radial expansion in the compacted soil layer generally also thickened in response to exogenous ethylene in hydroponic culture, that is, radial expansion in response to ethylene was correlated with the thickening response to impedance in soil. We propose that ethylene insensitive roots, that is, those that do not thicken and can overcome impedance, have a competitive advantage under mechanically impeded conditions as they can maintain their elongation rates. We suggest that prolonged exposure to ethylene could function as a stop signal for axial root growth.
径向扩展是根系对机械阻抗的一种经典反应，一般认为这种反应有助于根系穿透土壤。我们分析了玉米节根对阻抗的反应，以验证以下假设：径向扩展与根系穿过压实土层的能力无关。不同基因型根系穿过压实土层的能力存在差异，那些对压实土层的趋近角度更陡或在压实土层中径向扩展较小的基因型更有可能穿过该土层并达到更深的深度。根的径向扩展是由于皮层细胞大小的增加，而皮层细胞列数保持不变。在压实土层中表现出径向扩展的基因型和节根类别，在水培条件下通常也会对外源乙烯作出增粗反应，也就是说，对乙烯的径向扩展反应与在土壤中对阻抗的增粗反应相关。我们提出，对乙烯不敏感的根系，即那些不会增粗且能克服阻抗的根系，在机械阻抗条件下具有竞争优势，因为它们能够保持伸长率。我们认为，长时间暴露于乙烯可能作为轴向根生长的停止信号。
