Crassulacean Acid Metabolism

Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO₂). The CO₂ is stored as the four-carbon acid malate in vacuoles at night, and then in the daytime, the malate is transported to chloroplasts where it is converted back to CO₂, which is then used during photosynthesis. The pre-collected CO₂ is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency. This metabolism was first studied in plants of the Crassulaceae family. These mainly include succulents. The first time it was studied, Crassula was used as a model organism.

CAM was first suspected by de Saussure in 1804 in his Recherches Chimiques sur la Vegetation, confirmed and refined by Aubert, E. in 1892 in his Recherches physiologiques sur les plantes grasses and expounded upon by Richards, H. M. 1915 in Acidity and Gas Interchange in Cacti, Carnegie Institution. The term CAM may have been coined by Ranson and Thomas in 1940, but they were not the first to discover this cycle. It was observed by the botanists Ranson and Thomas, in the Crassulaceae family of succulents (which includes jade plants and Sedum). Its name refers to acid metabolism in Crassulaceae, not the metabolism of "crassulacean acid".

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