Crassulacean acid metabolism
Crassulacean acid metabolism
CAM plants, acronym for “Crassulacean Acid Metabolism” are a type of plant that have developed a particular strategy to deal with the problems related to photosynthesis in arid or dry environments, where water is scarce and temperatures can be high.
Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. In a plant using full CAM, the stomata of the leaves remain closed during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2) and allow it to diffuse into the mesophyll cells. CO2 is stored as four-carbon malic acid in vacuoles at night, then during the day the malate is transported to the chloroplasts where it is converted back to CO2, which is then used during photosynthesis. Pre-harvested CO2 concentrates around the RuBisCO enzyme, increasing photosynthetic efficiency.
With this mechanism, CAM plants reduce the loss of water through transpiration during the day, when temperatures are high and humidity is low. Unlike most plants, which open their stomata (small openings on the surface of leaves) during the day to capture carbon dioxide (CO2) for photosynthesis, CAM plants only open their stomata at night.
In this way, as mentioned, the photosynthetic process of CAM plants is divided into two main phases: the fixation of carbon dioxide (CO2) and the actual photosynthesis.
1. CO2 Fixation: Unlike C3 and C4 plants, which fix CO2 using the Rubisco enzyme during the day, CAM plants do this at night. During the night, their stomata open and absorb the CO2 present in the atmosphere. This CO2 is converted into a different chemical form, malic acid, and stored in leaf cells.
2. Photosynthesis during the day: During the day, the stomata of CAM plants remain closed to avoid water loss through transpiration. Instead, the malic acid stored in the leaf cells is transformed back into CO2, which is used for photosynthesis through the normal Calvin cycle. This stage occurs in a light-rich environment, allowing the plant to produce glucose and other nutrients necessary for its survival.
This process reduces water loss because plants avoid opening their stomata during the day, when the risk of excessive transpiration would be greatest.
CAM plants were initially discovered in some species of the Crassulaceae family (from which their mechanism takes its name), but later it was discovered that many other groups of plants have developed this adaptive strategy to survive in harsh environments. Some examples of CAM plants include some species of cacti, agave, succulent plants and some orchids.
This type of metabolism is an important adaptation for the survival of plants in arid environments or with scarce water resources, allowing them to conserve water and maintain photosynthesis despite unfavorable conditions.
In summary, CAM plants can be considered “stomatically independent” because they fix CO2 during the night when the stomata are open and then carry out photosynthesis during the day when the stomata are closed. This mechanism allows CAM plants to reduce water loss and effectively adapt to harsh environmental conditions, such as those found in arid and desert habitats.
Fonte foto:
– https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism#/media/File:CAM_cycle_English.svg