Winter Klaus, Holtum Joseph A M
Smithsonian Tropical Research Institute, PO Box 0843-03092, Panama City, Panama.
College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia.
J Plant Physiol. 2024 Mar;294:154185. doi: 10.1016/j.jplph.2024.154185. Epub 2024 Jan 28.
Five decades ago, the first report of a shift from C to CAM (crassulacean acid metabolism) photosynthesis following the imposition of stress was published in this journal. The annual, Mesembryanthemum crystallinum (Aizoaceae), was shown to be a C plant when grown under non-saline conditions, and a CAM plant when exposed to high soil salinity. This observation of environmentally triggered CAM eventually led to the introduction of the term facultative CAM, which categorises CAM that is induced or upregulated in response to water-deficit stress and is lost or downregulated when the stress is removed. Reversibility of C-to-CAM shifts distinguishes stress-driven facultative-CAM responses from purely ontogenetic increases of CAM activity. We briefly review how the understanding of facultative CAM has developed, evaluate the current state of knowledge, and highlight questions of continuing interest. We demonstrate that the long-lived leaves of a perennial facultative-CAM arborescent species, Clusia pratensis, can repeatedly switch between C and CAM in response to multiple wet-dry-wet cycles. Undoubtedly, this is a dedicated response to environment, independent of ontogeny. We highlight the potential for engineering facultative CAM into C crops to provide a flexible capacity for drought tolerance.
五十年前，本期刊发表了首篇关于胁迫下光合作用从C途径转变为景天酸代谢（CAM）途径的报告。一年生植物冰花（番杏科）在非盐渍条件下生长时表现为C植物，而在高土壤盐分条件下则表现为CAM植物。这种对环境诱导的CAM的观察最终导致了兼性CAM这一术语的引入，它将因水分亏缺胁迫而诱导或上调，在胁迫解除后又丧失或下调的CAM进行分类。从C途径到CAM途径转变的可逆性将胁迫驱动的兼性CAM反应与CAM活性单纯的个体发育增加区分开来。我们简要回顾了对兼性CAM的理解是如何发展的，评估了当前的知识状态，并突出了持续受到关注的问题。我们证明，多年生兼性CAM乔木物种普拉滕西亚克鲁西亚（Clusia pratensis）的长寿叶片能够响应多个干湿循环在C途径和CAM途径之间反复切换。毫无疑问，这是一种对环境的专门响应，与个体发育无关。我们强调了将兼性CAM引入C作物以提供灵活耐旱能力的潜力。
