Mayr S, Kartusch B, Kikuta S
Institute of Botany, University of Innsbruck, 6020 Innsbruck, Austria.
Institute of Botany, University of Natural Resources and Life Sciences, BOKU Vienna, 1180 Vienna, Austria.
J Plant Hydraul. 2014;1. doi: 10.20870/jph.2014.e004.
Water transport in plants is based on a metastable system as the xylem "works" at negative water potentials (ψ). At critically low ψ, water columns can break and cause embolism. According to the air-seeding hypothesis, this occurs by air entry via the pits. We studied the formation of embolism in dehydrating xylem sections of (Cupressaceae), which were monitored microscopically and via ultrasonic emission analyses. After replacement of water by air in outer tracheid layers, a complex movement of air-water menisci into tracheids was found. With decreasing ψ, pits started to aspirate and the speed of menisci movements increased. In one experiment, an airseeding event could be detected at a pit. The onset of ultrasonic activity was observed when pits started to close, and ultrasonic emission ceased at intense dehydration. Experiments clearly indicated that predictions of the air-seeding hypothesis are correct: At low ψ, pit mechanisms to prevent air entry failed and air spread into tracheids. ψ fluctuations caused complex movements of air-water menisci and pits, and at low ψ, air-seeding caused ultrasonic emissions. Main insights are presented in a video.
植物中的水分运输基于一个亚稳系统，因为木质部在负水势（ψ）下“工作”。在极低的ψ时，水柱会断裂并导致栓塞。根据气核引入假说，这是通过纹孔进入空气而发生的。我们研究了柏科植物脱水木质部切片中栓塞的形成，通过显微镜和超声发射分析对其进行监测。在外层管胞层中的水被空气取代后，发现气 - 水弯月面进入管胞的复杂运动。随着ψ降低，纹孔开始吸气，弯月面运动速度增加。在一个实验中，在一个纹孔处检测到了气核引入事件。当纹孔开始关闭时观察到超声活动的开始，在强烈脱水时超声发射停止。实验清楚地表明气核引入假说的预测是正确的：在低ψ时，防止空气进入的纹孔机制失效，空气扩散到管胞中。ψ波动导致气 - 水弯月面和纹孔的复杂运动，并且在低ψ时，气核引入导致超声发射。主要见解在一个视频中展示。
