Crassulaceae family

Although first discovered in species of the Crassulaceae, the presence of CAM is now well established in various families of higher plants with succulent stems or leaves [15]. 

ROSEROOT, Sedi rosei rhizoma The drug consists of the rhizome of Sedum roseum (L.). Scop. (syn. Rhodiola rosea L.), family Crassulaceae. 

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. 

IsocHricacid HOOC-CH2-CH(COOH)-CHOH-COOH, a monohydroxy tricarboxylic acid, an isomer of citric acid, which is widely distributed in the plant kingdom and occurs in free form especially in plants of the stone-crop family (Crassulaceae), and in fruits. The salts of I. a., isocitrates, are important metaboli-cally as intermediates in the Tricarboxylic acid cycle (see), where they are formed from citrate by the enzyme aconitase, then oxidized to 2-oxoglutarate. In the Glyoxylate cycle (see), isocitrate is cleaved to succinate and glyoxylate. 

Malic acid monohydroxysuccinic acid, HOOC-CHOH-CHj- OOH, a dicarboxylic acid found in many plant juices, usually in the L(-i-)-form, m.p. 100°C, b.p. 140°C (d.). The malate ion is formed in the Thcarboxylic acid cycle (see) and in the Glyoxy-late cycle (see). Malate plays an important role in the Diurnal acid rhythm (see) of the Crassulaceae (stonecrop family). 

Occurrence in Non-solanaceous/Non-convolvulaceous Taxa. Later it was reported that hygrine and/or closely related derivatives are also constituents of different unrelated families found throughout the plant kingdom. Such sporadic occurrence was discovered - besides the Erythroxylaceae (see above) - for certain Sedum spp. (Crassulaceae) (Stevens et al. 1992 Kim et al. 1996), Carallia brachiata (Lour.) Merr. (Rhizophoraceae), Cochlearia arctica Slecht (Brassicaceae), as well as for Dendrobium chrysanthum Wall. (Orchidaceae) (Massiot and Delaude 1986 and references therein) and Picea breweriana S.Watson, Pinaceae (Schneider et al. 1995). 

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. 

The Crassulaceae are a reasonably large family with some 30 or more genera and over 1000 species. The largest genera are Crassula, Sedum, and Kalanchoe. Most are distinctly leaf succulents (Lawrence, 1955). 

Of the 11 succulent families surveyed by Dittrich et al. (1973) the Asclepiada-ceae, Bromeliaceae, Euphorbiaceae, Liliaceae, and Vitaceae had substantial PEP carboxykinase activity (a mean of about 8 pmol min" mg chi" ). The remaining seven families (Agavaceae, Aizoaceae, Asteraceae, Cactaceae, Crassulaceae, Orchidaceae, and some members of the Liliaceae) showed little or no PEP carboxykinase activity. 

Finally, virtually all the CAM plant families have some economic importance as ornamentals. Perhaps the most important are the Crassulaceae and the Cacta-ceae, but the orchids and bromeliads are extensively used. 

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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