Dynamic surface tension of xylem sap lipids.
Dynamic surface tension of xylem sap lipids.
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DOI：
10.1093/treephys/tpaa006
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发表时间：
2020-02
期刊：
影响因子：
4
通讯作者：
Jinlong Yang;Joseph M Michaud;S. Jansen;H. J. Schenk;Yi Y. Zuo
中科院分区：
文献类型：
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作者：
Jinlong Yang;Joseph M Michaud;S. Jansen;H. J. Schenk;Yi Y. Zuo
传统上认为木质部汁液的表面张力与纯水的表面张力接近，因为表面张力的降低被认为会增加对空气播种和栓塞的脆弱性。然而，木质部汁液含有不溶性的基于脂质的表面活性剂，其也涂覆容器和纹孔膜表面，在称为空气播种的过程中，气泡可以在负压下进入木质部。由于两亲性脂质的不溶性，在坑孔中影响空气播种的表面张力不是所提取的大体积树液的平衡表面张力，而是在气-液界面处的局部表面张力，其动态地取决于单位表面积的脂质的局部浓度。为了估计木质部质外体表面的脂质层中的动态表面张力，我们研究了时间依赖性和表面积调节的表面张力的质外体脂质提取的木质部汁液的四个木本被子植物植物使用约束滴表面测定法（CDS）。木质部脂质被发现表现出有效的表面活性，当在平衡表面积周围的50%和160%之间改变表面积时，表面张力在约25 mN/m达到平衡，并且在最小19 mN/m和最大68 mN/m之间变化。它的结论是，木质部脂质膜在自然条件下最有可能的范围从非平衡亚稳态条件下的过饱和压缩状态的不饱和膨胀状态，这取决于局部表面积的气液界面。与被子植物孔膜的最大孔收缩比以前假设的要小得多的发现，木质部的低动态表面张力原来是完全兼容的凝聚力张力和空气播种理论，以及与木质部汁液中存在的脂质涂层的纳米气泡，并与在植物中观察到的栓塞的脆弱性的范围。
The surface tension of xylem sap has been traditionally assumed to be close to that of the pure water because decreasing surface tension is thought to increase vulnerability to air seeding and embolism. However, xylem sap contains insoluble lipid-based surfactants, which also coat vessel and pit membrane surfaces, where gas bubbles can enter xylem under negative pressure in the process known as air seeding. Because of the insolubility of amphiphilic lipids, the surface tension influencing air seeding in pit pores is not the equilibrium surface tension of extracted bulk sap but the local surface tension at gas-liquid interfaces, which depends dynamically on the local concentration of lipids per surface area. To estimate the dynamic surface tension in lipid layers that line surfaces in the xylem apoplast, we studied the time-dependent and surface area-regulated surface tensions of apoplastic lipids extracted from xylem sap of four woody angiosperm plants using constrained drop surfactometry (CDS). Xylem lipids were found to demonstrate potent surface activity, with surface tensions reaching an equilibrium at ~25 mN/m and varying between a minimum of 19 mN/m and a maximum of 68 mN/m when changing the surface area between 50 and 160% around the equilibrium surface area. It is concluded that xylem lipid films in natural conditions most likely range from nonequilibrium metastable conditions of a supersaturated compression state to an undersaturated expansion state, depending on the local surface areas of gas-liquid interfaces. Together with findings that maximum pore constrictions in angiosperm pit membranes are much smaller than previously assumed, low dynamic surface tension in xylem turns out to be entirely compatible with the cohesion-tension and air-seeding theories, as well as with the existence of lipid-coated nanobubbles in xylem sap, and with the range of vulnerabilities to embolism observed in plants.