Reversible Deformation of Transfusion Tracheids in Taxus baccata Is Associated with a Reversible Decrease in Leaf Hydraulic Conductance1[OPEN]
Reversible Deformation of Transfusion Tracheids in Taxus baccata Is Associated with a Reversible Decrease in Leaf Hydraulic Conductance1[OPEN]
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DOI：
10.1104/pp.114.243105
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发表时间：
2014-06
期刊：
影响因子：
7.4
通讯作者：
Yong-Jiang Zhang;F. E. Rockwell;James K. Wheeler;N. Holbrook
中科院分区：
文献类型：
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作者：
Yong-Jiang Zhang;F. E. Rockwell;James K. Wheeler;N. Holbrook
干燥条件下，红豆杉叶片输血管的可逆坍缩与叶片水力导度的可逆下降有关，表明其具有类似断路器的功能，保护木质部免受过度紧张的影响。叶片水力导度（Kleaf）随水分胁迫的增加而下降归因于叶片木质部的空化。然而，在针叶树的叶子中，输注气管的可逆塌陷可能提供了另一种解释。利用红豆杉（Taxus baccata，一种没有树脂的针叶树），我们开发了一种改进的复水技术，该技术允许在水势松弛到- 1 MPa时将Kleaf的下降分为两个组分：一个可逆组分和一个不可逆组分。我们使用冷冻扫描电镜观察了叶片在水势范围内的空化证据，并使用冷冻荧光显微镜量化了脱水引起的输注气管结构变化。当叶片水势大于- 3 MPa时，叶片水分不可逆下降。低温荧光显微镜显示，在−2和−3 MPa之间，Kleaf下降是可逆的，并伴有输注气管塌陷。低温扫描电镜结果显示，输注或木质部管胞空化均未导致叶片叶片在可逆范围内的下降。此外，输注气管的变形是很快可逆的，因此作为一个断路器调节通过叶片脉管系统的水通量。由于输注组织存在于所有裸子植物中，输注管的可逆塌陷可能是裸子植物保护叶木质部免受活叶组织产生的过度负荷的一般机制。
The reversible collapse of leaf transfusion tracheids of Taxus baccata under desiccation is related to reversible declines in leaf hydraulic conductance, suggesting a circuit breaker-like function that protects the xylem from excessive tensions. Declines in leaf hydraulic conductance (Kleaf) with increasing water stress have been attributed to cavitation of the leaf xylem. However, in the leaves of conifers, the reversible collapse of transfusion tracheids may provide an alternative explanation. Using Taxus baccata, a conifer species without resin, we developed a modified rehydration technique that allows the separation of declines in Kleaf into two components: one reversible and one irreversible upon relaxation of water potential to −1 MPa. We surveyed leaves at a range of water potentials for evidence of cavitation using cryo-scanning electron microscopy and quantified dehydration-induced structural changes in transfusion tracheids by cryo-fluorescence microscopy. Irreversible declines in Kleaf did not occur until leaf water potentials were more negative than −3 MPa. Declines in Kleaf between −2 and −3 MPa were reversible and accompanied by the collapse of transfusion tracheids, as evidenced by cryo-fluorescence microscopy. Based on cryo-scanning electron microscopy, cavitation of either transfusion or xylem tracheids did not contribute to declines in Kleaf in the reversible range. Moreover, the deformation of transfusion tracheids was quickly reversible, thus acting as a circuit breaker regulating the flux of water through the leaf vasculature. As transfusion tissue is present in all gymnosperms, the reversible collapse of transfusion tracheids may be a general mechanism in this group for the protection of leaf xylem from excessive loads generated in the living leaf tissue.