Boyer John S
College of Earth, Ocean and Environment (formerly Marine Biology/Biochemistry Program), College of Marine Studies, University of Delaware, Lewes, DE 19958, USA
J Exp Bot. 2015 May;66(9):2625-33. doi: 10.1093/jxb/erv065. Epub 2015 Mar 3.
Leaf photosynthesis relies on CO₂ diffusing in while water vapour diffuses out. When stomata close, cuticle waxes on the epidermal tissues increasingly affect this diffusion. Also, changes in turgor can shrink or swell a leaf, varying the cuticle size. In this study, the properties of the cuticle were investigated while turgor varied in intact leaves of hypo stomatous grape (Vitis vinifera L.) or amphistomatous sunflower (Helianthus annuus L.). For grape, stomata on the abaxial surface were sealed and high CO₂ concentrations outside the leaf were used to maximize diffusion through the adaxial, stoma-free cuticle. For sunflower, stomata were closed in the dark or with abscisic acid to maximize the cuticle contribution to the path. In both species, the internal CO₂ concentration was measured directly and continuously while other variables were determined to establish the cuticle properties. The results indicated that stomatal closure diminished the diffusion of both gases in both species, but for CO₂ more than for water vapour. Decreasing the turgor diminished the movement of both gases through the cuticle of both species. Because this turgor effect was observed in the adaxial surface of grape, which had no stomata, it could only be attributed to cuticle tightening. Comparing calculated and measured concentrations of CO₂ in leaves revealed differences that became large as stomata began to close. These differences in transport, together with turgor effects, suggest calculations of the CO₂ concentration inside leaves need to be viewed with caution when stomata begin to close.
叶片光合作用依赖于二氧化碳的扩散进入以及水蒸气的扩散出去。当气孔关闭时，表皮组织上的角质层蜡质对这种扩散的影响日益增大。此外，膨压的变化会使叶片收缩或膨胀，从而改变角质层的大小。在本研究中，对气孔下生的葡萄（欧亚种葡萄）或双面气孔的向日葵（向日葵）完整叶片在膨压变化时的角质层特性进行了研究。对于葡萄，将叶片背面的气孔密封，并使用叶片外部的高二氧化碳浓度来最大化通过叶片正面无气孔角质层的扩散。对于向日葵，在黑暗中或使用脱落酸使气孔关闭，以最大化角质层对扩散路径的贡献。在这两个物种中，直接且连续地测量内部二氧化碳浓度，同时测定其他变量以确定角质层特性。结果表明，气孔关闭减少了这两个物种中两种气体的扩散，但对二氧化碳的影响大于对水蒸气的影响。降低膨压减少了这两个物种中两种气体通过角质层的移动。由于在没有气孔的葡萄叶片正面观察到了这种膨压效应，它只能归因于角质层的收紧。比较叶片中计算得出的和测量得到的二氧化碳浓度，发现随着气孔开始关闭，差异变得很大。这些传输差异以及膨压效应表明，当气孔开始关闭时，对叶片内部二氧化碳浓度的计算需要谨慎看待。
