Crassulacean Acid Metabolism (CAM Pathway)

Crassulacean

Acid

Metabolism

(CAM Pathway)

Group 4

Simon Tantuan

Iana Tan

Shaira Sandigan

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 : Phosphoenolpyruvic acid

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 xerophyticcharacters, 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.

SUMMARY

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!

Hi there!

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!

Thanks Mr. Cactus. And

thank you listeners!