Water stress deforms tracheids peripheral to the leaf vein of a tropical conifer
Water stress deforms tracheids peripheral to the leaf vein of a tropical conifer
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DOI：
10.1104/pp.104.058156
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发表时间：
2005-03-01
期刊：
影响因子：
7.4
通讯作者：
Holbrook, NM
中科院分区：
文献类型：
--
作者：
Brodribb, TJ;Holbrook, NM
就像湿透的纸质稻草在口渴的饮水者施加的吸力下容易屈服一样，树叶中的木质部管胞似乎容易随着水势的下降而崩溃，阻碍它们的功能。在这里，我们描述了在张力下，阔叶雨林针叶树叶脉周围木质化细胞的崩溃。罗汉果叶片的特征是与叶脉垂直排列的圆柱形管胞，显然参与了水分在叶肉中的径向分布。在叶片干燥过程中，这些管胞中的大多数在水势-1.5到-2.8兆帕的范围内从圆形坍塌到平面。叶片导水率(K叶)的下降反映了水分胁迫下管胞塌陷百分率的增加，这对水分运输效率有直接影响。气孔对水分胁迫的响应是在-2.0 Mpa下关闭，此时有45%的细胞坍塌，K叶下降了25%。这仍然大大早于最初的迹象，即空化导致叶片叶脉在-3兆帕下失去水力传导性。干旱至49%的管胞崩溃的植株在复水后1周完全恢复管胞形状和叶片功能。一个简单的管胞塌陷力学模型，从管子的理论屈曲压力出发，准确地预测了在F.grayi观察到的塌陷动力学，证实了对细胞壁弹性和测量的叶水势的估计。讨论了可塌陷血管组织可能的适应性优势。
Just as a soggy paper straw is prone to yielding under the applied suction of a thirsty drinker, the xylem tracheids in leaves seem prone to collapse as water potential declines, impeding their function. Here we describe the collapse, under tension, of lignified cells peripheral to the leaf vein of a broad-leaved rainforest conifer, Podocarpus grayi de Laub. Leaves of Podocarpus are characterized by an array of cylindrical tracheids aligned perpendicular to the leaf vein, apparently involved in the distribution of water radially through the mesophyll. During leaf desiccation the majority of these tracheids collapsed from circular to flat over the water potential range -1.5 to -2.8 MPa. An increase in the percentage of tracheids collapsed during imposed water stress was mirrored by declining leaf hydraulic conductivity (K-leaf) implying a direct effect on water transport efficiency. Stomata responded to water stress by closing at -2.0 MPa when 45% of cells were collapsed and K-leaf had declined by 25%. This was still substantially before the initial indications of cavitation-induced loss of hydraulic conductance in the leaf vein, at -3 MPa. Plants droughted until 49% of tracheids had collapsed were found to fully recover tracheid shape and leaf function 1 week after rewatering. A simple mechanical model of tracheid collapse, derived from the theoretical buckling pressure for pipes, accurately predicted the collapse dynamics observed in F. grayi, substantiating estimates of cell wall elasticity and measured leaf water potential. The possible adaptive advantages of collapsible vascular tissue are discussed.