Crassulacean acid metabolism
From Free net encyclopedia
Crassulacean acid metabolism (CAM) is a carbon fixation pathway in some photosynthetic plants. CAM is usually found in plants living under arid conditions, including those found in the desert (for example, cacti or pineapple). It is named after the plant family it was first discovered in, the Crassulaceae.
Synopsis
Plants that are adapted to dry climates are called xerophytes. Some of these plants have small, thick leaves with a reduced surface area. They may also have a thickened cuticle to protect themselves from the environment. The stomata may be sunken into pits. Some xerophytes shed their leaves during the driest seasons and others can store water such as cacti. CAM plants uptake CO2 at night and store it as malic acid that can be broken down during the day for sugars.
These plants close their stomata (tiny pores used for gas exchange) during the day in order to conserve water. Normally, they wouldn't be able to carry out photosynthesis, since carbon dioxide from the air wouldn't be available. Therefore, their stomata are open during the night, and it is then that they take in carbon dioxide. They store it as malate and other, simple organic compounds. Malate in particular is easily broken down into pyruvate, which can be phosphorylated into PEP and then be recycled to fix more carbon.
In some ways, CAM resembles C4 metabolism, except that CAM plants contain no bundle sheaths around their veins, and C4 metabolism is continuous (as long as there is light), while CAM only occurs at night. CAM metabolism is present in many plant families. An example of these plants are the cacti.da:CAM-plante de:CAM-Pflanzen es:Metabolismo ácido de las crassulaceae fr:Métabolisme acide crassulacéen ko:CAM 식물 ja:CAM型光合成 zh:景天酸代謝植物