Crassulaceae metabolism

CAM plants use the same chemistry but package it differently. Specifically, they lack the Kranz anatomy that is the defining characteristic of the C4 plants. Kranz is the German word for wreath and refers to the appearance—in a cross-sectioned leaf—of the cells which sheath the vascular bundles in C4 plants. CAM stands for Crassulacean Acid Metabolism. There is no such thing as crassulacean acid. The name instead refers to the initial discovery of this pathway of carbon fixation, in which oxaloacetic, malic, and pyruvic acids play key roles, in plants from the family Crassulaceae. cam plants open their stomata, take in CO2, and produce malate at night. Temperatures and, consequently, water losses are lower. During the day, the stomata are closed and the malate is processed as in the bundle-sheath cells of C4 plants. Diffusive losses of CO2 are, however, greater than those in C4 plants. 

Crassulacean acid metabolism (CAM) is yet another adaptation to increase the efficiency of the Calvin cycle. Crassulacean acid metabolism, named after the genus Crassulacea (the succulents), is a response to drought as well as warm conditions. In CAM plants, the stomata of the leaves are closed in... 

Crassulacean Acid Metabolism has been documented in at least 18 flowering plant families (Table 1.1). As of 1977, there were recorded in the literature 109 genera and over 300 species of flowering plants (cf. Black and Williams, 1976 Szarek and Ting, 1977) with CAM. The largest and most important CAM families are the Cactaceae, the Crassulaceae, the Euphorbiaceae, the Aizoaceae, and perhaps the Liliaceae, especially if Agavaceae are included with the lilies. The epiphytic forms of the Bromeliaceae and the Orchidaceae make these families important. 

Finally, it should be made clear that the Cactaceae type of CAM shift is quite different from the shift reported in the Aizoaceae, Portulacaceae, and certain Crassulaceae. In the latter, the response to photoperiod and water stress appear to be a real shift in metabolic pathway. Not only do acids begin to fluctuate concomitant with gas exchange at night, but enzymes change quantitatively. Hence, the evidence suggests a reversible shift from C3 to CAM. 

Reynolds, J.S., Kimbrough, T.D., and Weekley, L.B. (198A). Evidence for enzymatic 5-hydroxylation of indole-3-acetic acid m vitro by extracts of Sedum morganianum. Z. fur Pflanzenphysiol., 112, 465-470. Reynolds, J.D., Kimbrough, T.D., and Weekley, L.B. (1985). The effect of light quality on 5-hydroxyindole metabolism in leaves of Sedum morganianum (Crassulaceae). Biochem. Physiol. Pflanzen., 180,... 

A further modification (referred to as crassula-cean acid metabolism) is conducted by the family, Crassulaceae, mainly found in South Africa. These plants live in extremely arid conditions. To prevent dehydration, their stomata remain closed during daylight hours but open after dark to absorb COj which is fixed by the carboxylation of phospho-enolpyruvate to malate. Large quantities of malate can be stored in the large cellular vacuoles until the following day when decarboxylation of malate releases COj for photosynthesis. 

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