Ceusters Johan, Borland Anne M, De Proft Maurice P
Faculty of Bioscience Engineering, Department of Biosystems, Division of Crop Biotechnics, Katholieke Universiteit Leuven, Heverlee, Belgium.
Plant Signal Behav. 2009 Mar;4(3):212-4. doi: 10.4161/psb.4.3.7813.
Nocturnal CO uptake in CAM plants is sustained by the degradation of storage carbohydrate which provides the acceptor (PEP) for the nocturnal carboxylase (PEPC). The investment of resources into a transient storage carbohydrate pool unavoidably places restriction on other metabolic activities including dark respiration, growth and acclimation to abiotic stress. In our recent report the flexible use of different storage carbohydrate pools is shown to be involved in the acclimation process to drought and recovery from dehydration. While starch breakdown stoichiometrically accounts for nocturnal CO uptake under well-watered conditions, the sucrose pool is maintained in preference to starch during progressing drought and sucrose becomes the major source of carbon fuelling the dark reactions after 45 days of water deprivation. Re-watering plants results in a recovery to the original situation, with starch constituting the main carbohydrate reserve for nocturnal provision of PEP. However, substantial amounts of starch are also retained in the leaves of re-watered plants by restricting export/respiration and thus provides a potential buffer capacity against a return to water deprivation. This significant conservation of starch suggests the ability to perceive, remember and anticipate the formerly encountered drought stress in some way, with the adaptation of the equilibrium of carbohydrate balance as a central factor underpinning the physiological homeostasis of CAM plants.
景天酸代谢（CAM）植物夜间对二氧化碳的吸收由储存碳水化合物的降解维持，这些储存碳水化合物为夜间羧化酶（磷酸烯醇式丙酮酸羧化酶，PEPC）提供受体（磷酸烯醇式丙酮酸，PEP）。将资源投入到一个短暂的储存碳水化合物库不可避免地会限制其他代谢活动，包括暗呼吸、生长以及对非生物胁迫的适应。在我们最近的报告中，不同储存碳水化合物库的灵活利用被证明参与了干旱适应过程以及脱水后的恢复过程。在水分充足的条件下，淀粉分解在化学计量上解释了夜间对二氧化碳的吸收，而在干旱进展过程中，蔗糖库优先于淀粉得以维持，并且在缺水45天后，蔗糖成为为暗反应提供碳源的主要来源。给植物重新浇水会使其恢复到原来的状态，淀粉成为夜间提供PEP的主要碳水化合物储备。然而，通过限制输出/呼吸作用，大量淀粉也保留在重新浇水植物的叶片中，从而提供了一种潜在的缓冲能力，以应对再次缺水的情况。淀粉的这种显著保留表明植物能够以某种方式感知、记住并预测之前遇到的干旱胁迫，碳水化合物平衡的平衡调整作为一个核心因素支撑着CAM植物的生理稳态。
