Cryo-scanning electron microscopy observations of vessel content during transpiration in walnut petioles.: Facts or artifacts?
Cryo-scanning electron microscopy observations of vessel content during transpiration in walnut petioles.: Facts or artifacts?
复制标题
DOI：
10.1104/pp.124.3.1191
复制
发表时间：
2000-11-01
期刊：
影响因子：
7.4
通讯作者：
Cruiziat, P
中科院分区：
文献类型：
--
作者：
Cochard, H;Bodet, C;Cruiziat, P
目前关于植物中水分上升的“内聚-张力”的争论源于Canny及其同事（1995）最近对木质部导管含量的低温扫描电子显微镜（cryo-SEM）观察。在这些观察的基础上，有人声称，在蒸腾作用活跃的过程中，导管是排空和重新充盈的，这与以前的理论直接矛盾。在这项研究中，我们比较了冷冻扫描电镜数据与标准的液压方法对核桃（核桃）叶柄。这两种技术的结果是明显冲突的，不可能都是正确的。冷冻扫描电镜观察核桃叶柄冻结完整的树在一个浴的液氮（LN 2）表明，血管空化发生和扭转自己的昼夜基础上。中午时，多达30%的血管被栓塞。与此相反，切除叶柄段的水力传导度（PLC）的损失的百分比保持接近0%全天。为了找出哪种技术是错误的，我们首先分析了当木质部压力释放时PLC值迅速返回到零的可能性。我们使用离心力来测量叶柄段暴露于非常负的压力和建立这种技术的相关性的木质部电导。然后，我们分析了暴露于LN时血管部分充气的可能性。低温扫描电镜观察叶柄段冻结后不久，他们的木质部压力恢复到大气值完全同意与PLC值。我们证实，与充满水的毛细管暴露于一个大的离心力，这是不可能的冷冻完整的内容与液氮。我们的结论是，在我们的研究中，部分充满空气的管道是冷冻扫描电镜技术的工件。我们认为，最近发表的低温扫描电镜观察结果可能应该重新考虑我们的结果之前，他们可能会被用来作为反对凝聚力-张力理论的论据。
The current controversy about the "cohesion-tension" of water ascent in plants arises from the recent cryo-scanning electron microscopy (cryo-SEM) observations of xylem vessels content by Canny and coworkers (1995). On the basis of these observations it has been claimed that vessels were emptying and refilling during active transpiration in direct contradiction to the previous theory. In, this study we compared the cryo-SEM data with the standard hydraulic approach on walnut (Juglans regia) petioles. The results of the two techniques were in clear conflict and could not both be right. Cryo-SEM observations of walnut petioles frozen intact on the tree in a bath of liquid nitrogen (LN2) suggested that vessel cavitation was occurring and reversing itself on a diurnal basis. Up to 30% of the vessels were embolized at midday. In contrast, the percentage of loss of hydraulic conductance (PLC) of excised petiole segments remained close to 0% throughout the day. To find out which technique was erroneous we first analyzed the possibility that PLC values were rapidly returned to zero when the xylem pressures were released. We used the centrifugal force to measure the xylem conductance of petiole segments exposed to very negative pressures and established the relevance of this technique. We then analyzed the possibility that vessels were becoming partially air-filled when exposed to LN,. Cryo-SEM observations of petiole segments frozen shortly after their xylem pressure was returned to atmospheric values agreed entirely with the PLC values. We confirmed, with water-filled capillary tubes exposed to a large centrifugal force, that it was not possible to freeze intact their content with LN2. We concluded that partially air-filled conduits were artifacts of the cryo-SEM technique in our study. We believe that the cryo-SEM observations published recently should probably be reconsidered in the light of our results before they may be used as arguments against the cohesion-tension theory.