Crassulacean Acid Metabolism (CAM Pathway) Group 4 Simon Tantuan Iana Tan ShairaSandigan
Historical Background CAM was first discovered in the late 1940s. It was observed by the botanists Ranson and Thomas, in the Crassulaceae family of succulents (which includes jade plants and Sedum). Its name refers to acid metabolism in Crassulaceae, not the metabolism of Crassulacean acid.
What is Crassulacean Acid Metabolism? It is a carbon fixation pathway present in some plants. Also known as CAM photosynthesis. These plants fix carbon dioxide (CO2) during the night, storing it as the four-carbon acid malate.
The CO2 is released during the day, where it is concentrated around the enzyme RuBisCO, increasing the efficiency of photosynthesis. The CAM pathway allows stomata to remain shut during the day, reducing evapotranspiration; therefore, it is especially common in plants adapted to arid conditions. CAM plants ~> subset of C-4 plants
We know that RuBisCo can react to Carbon and Oxygen, right? Since this is the case, CAM plants can’t use this because the fixation process is too wasteful. Plants eventually had to “evolve” in order to be able to adapt to their environment. This is what happens to the CAM plants in order to have a more efficient photosynthesis:
The fixation process now occurs in mesophyll cells (found in the leaves) so that they will be more exposed to the air & in order to take in more CO2. The malate, which is the product of the fixation process, is pumped deeper in (the leaf) so that it won't be exposed to air and to oxygen. This is to avoid photorespiration and the wasteful process, since RuBisCo is used in the Calvin cycle.
The process is a lot like the C-4 pathway. CAM plants ~> subset of C-4 plants
Overview of CAM: a two-part cycle
During the night… The CAM plant's stomata are open, allowing CO2 to enter and be fixated as organic acids that are stored in vacuoles. The carbon dioxide is fixed in the mesophyll cell's cytoplasm by a PEP reaction.
PEP : Phosphoenolpyruvicacid
During the day the stomata are closed (thus preventing water loss), and the carbon is released to the Calvin cycle so that photosynthesis may take place.
During the day… The carbon in the organic acids is freed from the mesophyll cell's vacuoles and enters the chloroplast's stroma and, thus, into the Calvin cycle.
Identifying a CAM plant CAM can be considered an adaptation to arid conditions. CAM plants often display other xerophytic characters, such as thick, reduced leaves with a low surface-area-to-volume ratio; thick cuticle; and stomata sunken into pits. Some shed their leaves during the dry season; others (the succulents) store water in vacuoles. CAM plants not only are good at retaining water but also use nitrogen very efficiently.
CAM plants can also be recognized as plants whose leaves have an increasing sour taste during the night yet become sweeter-tasting during the day. This is due to malic acid stored in the vacuoles of the plants' cells during the night and then used up during the day.
The benefits of CAM The most important benefit to the plant is the ability to leave most leaf stomata closed during the day. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evapotranspiration, allowing CAM plants to grow in environments that would otherwise be far too dry.
CAM pathway is a carbon fixation pathway in some plants. These plants fix carbon during the night, storing it as the four-carbon acid malate.
CAM usually occurs in plants that are found in deserts, arid places, etc.
Let’s ask Mr. Cactus to tell you how he survives in the hot desert everyday!
It so hot here in the desert! But I don’t want my water to evaporate… AHA! I will use my Crassulacean Acid Metabolism!
Cactus: Here is how I do it!
We CAM plants are a subset of C-4 plants. So we have a (sort of) similar process with C-4 plants. But some of these plants grow in places where water is abundant like in the rainforest... So, they don't have to worry about losing water. But we do! We live in the desert. Our process becomes a little different now.
MY process becomes a little different now. I have to keep my stomata close during the day time so that not so much water will evaporate out of me. The problem? Photosynthesis can only occur in the day time because of the so-called LIGHT DEPENDENT REACTIONS! I also need photons, you know. HAHAY! OMG!
... But our kind has found a way to solve this. YIPPEE! We have decided that we will do carbon fixation AT NIGHT! O, ha?
So what I do every night is... Open my stomata Take in CO2 Do carbon fixation and make a four-carbon acid malate by using an enzyme called PEP carboxylase because it can only react to carbon. Since I can't do photosynthesis yet, I just store the malate in my BIG vacuoles.
When the sun is now up... I close my somata Start doing photosynthesis Since I can't take in CO2 now because my stomata are closed, I use the malate that has been stored in my vacuoles In the Calvin cycle, the RuBisCo will not be able to waste energy since it cannot react to oxygen anymore. The enzyme can only react to the carbon I can now produce sugar in a very efficient way!!!
So, do you get it now? Well, I have to go now. Bye!