Variation in the oxygen isotope ratio of phloem sap sucrose from castor bean. Evidence in support of the Peclet effect
Variation in the oxygen isotope ratio of phloem sap sucrose from castor bean. Evidence in support of the Peclet effect
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DOI：
10.1104/pp.123.2.671
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发表时间：
2000-06-01
期刊：
影响因子：
7.4
通讯作者：
Farquhar, GD
中科院分区：
文献类型：
--
作者：
Barbour, MM;Schurr, U;Farquhar, GD
理论表明，O-18在植物有机物质（Delta）源水以上的富集水平可以提供控制水分流失的综合指标。然而，我们对影响德尔塔的过程的理解仍然存在差距。一个这样的差距是在叶片内蒸发位点处的水的模拟富集与作为整体的叶片水的测量富集之间观察到的差异（Δ（L））。Farquhar和Lloyd（1993）认为这可能是由Peclet效应引起的。也不清楚叶片中形成的有机物质是否反映了叶片或Delta（L）内蒸发部位的水分富集。为了探讨蓖麻（Ricinus communis L.）将仍然附着在植物上的叶子密封在受控环境的气体交换室中，并使叶子与空气的蒸气压差发生阶跃变化。在平衡条件下，在叶与空气的蒸汽压差变化后，每小时从室内叶柄的切口收集一次蔗糖，持续6小时。韧皮部汁液中蔗糖的氧同位素组成（Delta（L））反映了模拟的Delta（L）。提出了一个描述同位素稳态下Delta（δ）的模型，并解释了实测Delta（δ）的96%变化。这些数据有力地支持了Peclet效应理论。
Theory suggests that the level of enrichment of O-18 above source water in plant organic material (Delta) may provide an integrative indicator of control of water loss. However, there are still gaps in our understanding of the processes affecting Delta. One such gap is the observed discrepancy between modeled enrichment of water at the sites of evaporation within the leaf and measured enrichment of the leaf water as a whole (Delta(L)). Farquhar and Lloyd (1993) suggested that this may be caused by a Peclet effect. It is also unclear whether organic material formed in the leaf reflects enrichment of water at the sites of evaporation within the leaf or Delta(L). To investigate this question castor bean (Ricinus communis L.) leaves, still attached to the plant, were sealed into a controlled-environment gas exchange chamber and subjected to a step change in leaf-to-air vapor pressure difference. Sucrose was collected from a cut on the petiole of the leaf in the chamber under equilibrium conditions and every hour for 6 h after the change in leaf-to-air vapor pressure difference. Oxygen isotope composition of sucrose in the phloem sap (Delta(suc)) reflected modeled Delta(L). A model is presented describing Delta(suc) at isotopic steady state, and accounts for 96% of variation in measured Delta(suc). The data strongly support the Peclet effect theory.