Bloom A J
Department of Biological Sciences, Stanford University, Stanford, California 94305.
Plant Physiol. 1979 Apr;63(4):749-53. doi: 10.1104/pp.63.4.749.
In experiments with the facultative Crassulacean acid metabolism (CAM) species, Mesembryanthemum crystallinum, only plants which received high levels of inorganic salts fixed substantial amounts of CO(2) by the CAM pathway. Equivalent osmolarities of polyethylene glycol 6000 did not yield any CAM fixation. Plant water potential and turgor pressure had no detectable influence on the amount of CAM fixation. These observations rule out the possibility that the inorganic ions were acting as osmotic agents.Carbon dioxide and water exchange analysis showed that when water supply was not limiting, salt-deprived plants sustained higher reductive pentose phosphate cycle carbon fixation rates than salt-treated plants. Under water stress conditions, salt-deprived plants using only the reductive pentose phosphate cycle pathway assimilated less carbon and were less efficient in their water use than salt-treated plants using predominately the CAM pathway. These results support the hypothesis that the ability to use the CAM pathway reduces the capacity for reductive pentose phosphate cycle fixation but permits higher productivity in water-limited environments.
在用兼性景天酸代谢（CAM）植物松叶菊进行的实验中，只有接受高浓度无机盐的植株才通过CAM途径固定大量二氧化碳。等渗的聚乙二醇6000不会产生任何CAM固定作用。植物水势和膨压对CAM固定量没有可检测到的影响。这些观察结果排除了无机离子作为渗透剂起作用的可能性。二氧化碳和水分交换分析表明，当水分供应不受限时，缺盐植株维持的还原戊糖磷酸循环碳固定速率高于经盐处理的植株。在水分胁迫条件下，仅使用还原戊糖磷酸循环途径的缺盐植株同化的碳较少，水分利用效率也低于主要使用CAM途径的经盐处理植株。这些结果支持了以下假设：使用CAM途径的能力降低了还原戊糖磷酸循环固定的能力，但在水分有限的环境中允许更高的生产力。
