Yang Dongmei, Pereira Luciano, Peng Guoquan, Ribeiro Rafael V, Kaack Lucian, Jansen Steven, Tyree Melvin T
College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
Laboratory of Crop Physiology, Department of Plant Biology, Institute of Biology, P.O. Box 6109, University of Campinas (UNICAMP), Campinas 13083-970, Brazil.
Tree Physiol. 2023 Jan 5;43(1):88-101. doi: 10.1093/treephys/tpac105.
The pneumatic method has been introduced to quantify embolism resistance in plant xylem of various organs by applying a partial vacuum to cut-open xylem. Despite the similarity in vulnerability curves between the pneumatic and other methods, a modeling approach is needed to investigate if changes in xylem embolism during dehydration can be accurately quantified based on gas diffusion kinetics. Therefore, a unit pipe pneumatic (UPPn) model was developed to estimate gas extraction from intact conduits, which were axially interconnected by inter-conduit pit membranes to cut-open conduits. The physical laws used included Fick's law for diffusion, Henry's law for gas concentration partitioning between liquid and gas phases at equilibrium and the ideal gas law. The UPPn model showed that 91% of the extracted gas came from the first five series of embolized, intact conduits and only 9% from the aqueous phase after 15 s of simulation. Considering alternative gas sources, embolism resistance measured with a pneumatron device was systematically overestimated by 2-17%, which corresponded to a typical measuring error of 0.11 MPa for P50 (the water potential equivalent to 50% of the maximum amount of gas extracted). It is concluded that pneumatic vulnerability curves directly measure embolism of intact conduits due to the fast movement of gas across interconduit pit membranes, while gas extraction from sap and diffusion across hydrated cell walls is about 100 times slower. We expect that the UPPn model will also contribute to the understanding of embolism propagation based on temporal gas dynamics.
通过对切开的木质部施加部分真空，已引入气动方法来量化各种器官植物木质部中的栓塞抗性。尽管气动方法与其他方法的脆弱性曲线相似，但仍需要一种建模方法来研究基于气体扩散动力学，脱水过程中木质部栓塞的变化是否能够被准确量化。因此，开发了一种单位管道气动（UPPn）模型来估计从完整导管中提取的气体，这些导管通过导管间纹孔膜轴向连接到切开的导管。所使用的物理定律包括用于扩散的菲克定律、用于平衡时液相和气相之间气体浓度分配的亨利定律以及理想气体定律。UPPn模型显示，在模拟15秒后，91%的提取气体来自前五组栓塞的完整导管，只有9%来自水相。考虑到其他气体来源，用气压计装置测量的栓塞抗性被系统地高估了2%-17%，这对应于P50（相当于最大气体提取量50%的水势）的典型测量误差0.11MPa。得出的结论是，由于气体在导管间纹孔膜上的快速移动，气动脆弱性曲线直接测量完整导管的栓塞，而从汁液中提取气体并通过水合细胞壁扩散的速度要慢约100倍。我们预计UPPn模型也将有助于基于时间气体动力学理解栓塞的传播。
