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CAM plants, metabolism and examples

CAM plants, metabolism and examples

CAM plants: examples of CAM plants, metabolism and difference with C3 plants and C4 plants. Elements of plant physiology and explanations.

After explaining the differences between C3 and C4 plants, I couldn't help but talk about theCAM plants.

The termCAMis an acronym is stands forCrassulacean Acid Metabolism, acid metabolism of crassulaceae. The CAM metabolism, for the first time it was in fact observed in the Crassulaceae family.

CAM plants

Plants C3, C4 and CAM plants have a different anatomy. CAM plants are characterized by aaquifer parenchymawith non-photosynthetic cells. This tissue has plant cells with a particularly pronounced vacuole responsible for water supply.

It is no coincidence that theCAM plantsthey see their natural habitat in areas with an arid climate, where the soil is dry and the air is clear. For this reason, theCAM plantshad to develop adaptation mechanisms both to limit the phenomenon of foliar transpiration (the loss of water through the foliar epidermis) and to increase the concentration of carbon dioxide at the level of the rubiscus, the enzyme that allows the fixation of carbon and the beginning of the Calvin cycle.

CAM metabolism

Since CAM plants live in arid climates, they keep their stomata closed during the day and open during the night to avoid desiccation. For this reason, carbon organization and decarboxylation take place at two different times: day and night.

During the night, the stomata are open, CO2 enters and dissolves in the bicarbonate ion. The bicarbonate ion is used by the enzyme PEP-carboxylase to fix the carbon on an oxaloacetate molecule.

Thanks to a dehydrogenase, oxaloacetate is reduced in malic acid. Malic acid is gradually accumulated in the vacuole.

During the day the situation is reversed. The patient escapes from the vacuoles and is transferred to the chloroplasts where the NADP-dependent malic enzyme is present. This enzyme releases CO2 (and pyruvate) from malic acid thus operating the decarboxylation useful for increasing the CO2 levels available to RUBISCO.

During the day, the activity of the rubisk is guaranteed by photosynthesis and the Calvin cycle can start thanks to the high levels of CO2 due to the decarboxylation of malic acid accumulated during the night.

With theCAM metabolism, during the day, even if the stomata are closed and gas exchanges with the outside cease, the Rubisco still has a large amount of CO2 available.

Difference between CAM and C4 plants

The CAM plants and C4 plants they have a lot in common. They both have aaccumulation of carbon dioxide, a mechanism that is completely missing in theplants C3.

In theplants C4, however, both the carboxylation operated by the PEP-Carboxylase enzyme and the decarboxylation operated by the NADP-dependent malic enzyme, occur during the day.

In CAM there is a temporal separation of the two phases: day and night. In theplants C4there is a separationstructural, in fact the carboxylation occurs in the cells of the foliar mesophyll where the PSII is present and the steal is absent while the decarboxylation takes place in the chloroplasts of the cells of the collar sheath, here the steal is present but the PSII is absent.

The absence of the PSII is clear. Photosystem II is absent where it is present I steal it simply to avoid the production of Oxygen. The PSII, in fact, is associated with the oxygen evolving system, a hydrophobic pocket that strips electronics from the water (photolysis) allowing the release of O2 in the chloroplast.

Oxygen is a competitive inhibitor of CO2. ThereI steal, in fact, it can react with both carbon dioxide and molecular oxygen. To understand how Rubisco works, I invite you to read the dedicated paragraph in the article on the differences between C3 plants and C4 plants.

Examples of CAM plants

When it comes toCAM plantsone immediately thinks of succulent plants. It is true, succulent plants are an example of plants with CAM metabolism but other plants such as orchids or pineapples are also CAM plants.


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Video: How C3, C4 and CAM Plants Do Photosynthesis (January 2022).