Xylem wall collapse in water-stressed pine needles
Xylem wall collapse in water-stressed pine needles
复制标题
DOI：
10.1104/pp.103.028357
复制
发表时间：
2004-01-01
期刊：
影响因子：
7.4
通讯作者：
Coutand, C
中科院分区：
文献类型：
--
作者：
Cochard, H;Froux, F;Coutand, C
在木质部导管壁加固被认为是防止壁内爆的负压，但在水分胁迫过程中的木质部几何形状的直接观察仍然是在很大程度上缺乏。在这项研究中，我们分析了木质部的几何形状在水分胁迫过程中的变化，在四个松树种（松属）针叶。将脱水针叶用液氮冷冻，并用冷冻扫描电子显微镜和落射荧光显微镜观察仍然冷冻的木质部横截面。在干旱期间木质部压力的减少引起了一个渐进的管胞塌陷低于特定的阈值压力（P-塌陷），与茎中的空化的发病。P-崩溃是更负的管胞直径较小，壁厚的物种，这表明木质部效率，木质部容易崩溃，和壁硬化的成本之间的权衡。在严重脱水时，管胞壁完全塌陷，但管腔仍然充满树液。当进一步脱水时，管胞栓塞，管壁松弛。脱水针头的管壁塌陷在再水化后迅速逆转。我们讨论了这一新的水力性状的木质部功能和松树水关系的理解的影响。
Wall reinforcement in xylem conduits is thought to prevent wall implosion by negative pressures, but direct observations of xylem geometry during water stress are still largely lacking. In this study, we have analyzed the changes in xylem geometry during water stress in needles of four pine species (Pinus spp.). Dehydrated needles were frozen with liquid nitrogen, and xylem cross sections were observed, still frozen, with a cryo-scanning electron microscope and an epifluorescent microscope. Decrease in xylem pressure during drought provoked a progressive collapse of tracheids below a specific threshold pressure (P-collapse) that correlates with the onset of cavitation in the stems. P-collapse was more negative for species with smaller tracheid diameter and thicker walls, suggesting a tradeoff between xylem efficiency, xylem vulnerability to collapse, and the cost of wall stiffening. Upon severe dehydration, tracheid walls were completely collapsed, but lumens still appeared filled with sap. When dehydration proceeded further, tracheids embolized and walls relaxed. Wall collapse in dehydrated needles was rapidly reversed upon rehydration. We discuss the implications of this novel hydraulic trait on the xylem function and on the understanding of pine water relations.