Difference Between C4 and CAM Plants

The key difference between C4 and CAM plants is that in C4 plants, carbon fixation takes place in both mesophyll and bundle sheath cells while in CAM plants, carbon fixation takes place only in mesophyll cells.

Most of the plants follow the Calvin cycle, which is the C3 photosynthesis pathway. These plants grow in regions where there is adequate water availability. Furthermore, more than 90% of plants carry out the C3 pathway of carbohydrate synthesis. However, there are two other plant categories as well. They are C4 plants and CAM plants. But C4 plants and CAM plants are present in dry regions with a limited amount of water. They utilize special carbon fixation pathways to fix carbon and also to preserve the water content in their plant bodies.

CONTENTS

1. Overview and Key Difference
2. What are C4 Plants
3. What are CAM Plants
4. Similarities Between C4 and CAM Plants
5. Side by Side Comparison – C4 vs CAM Plants in Tabular Form
6. Summary

What are C4 Plants?

C4 plants are the type of plants that produce a 4-carbon compound; oxaloacetate as the first stable product of carbon fixation process. C4 plants are mesophytic. Therefore, C4 plants utilize C4 photosynthesis pathway. It is an alternative pathway to minimize the opening of stomata during day time and to increase the efficiency of Rubisco, which is the enzyme initially involved during carbon fixation. Accordingly, it takes place in both mesophyll cells and bundle sheath cells. This specialized structure where C4 photosynthesis takes place is Kranz anatomy.

Likewise, during C4 photosynthesis, the C4 plants use phosphoenolpyruvate (PEP) (an alternate enzyme present in the mesophyll cells) during the initial step of carbon fixation. PEP has a higher affinity for carbon dioxide than rubisco. Hence, carbon dioxide is fixed by PEP into oxaloacetate (C4) then to malate (C4) and transported to bundle sheath cells. Here, malate gets decarboxylated into pyruvate and carbon dioxide. This carbon dioxide is then fixed by Rubisco, present in bundle sheath cells. In the C4 pathway, carbon dioxide fixes at two regions of the leaf.

What are CAM Plants?

CAM plants are a type of plants which utilize CAM photosynthesis. CAM is Crassulacean acid metabolism. It is a special carbon fixation pathway present in plants that grow under arid conditions. Also, this mechanism was first found in the plant family Crassulaceae. Furthermore, this mechanism occurs during day time where the stomata present in leaves are kept closed.

Therefore, CAM photosynthesis prevents the water loss by the plant due to evaporation and transpiration. But during the night, stomata open and collect Carbon dioxide. Then this absorbed carbon dioxide stores as malate; a four-carbon compound in the vacuoles. Malate is derived from oxaloacetate which is the first stable compound produced by CAM plants during the night. It is then transported to the chloroplasts and converted back to carbon dioxide during day time to facilitate photosynthesis. Here, the first stable product synthesized is 3-phosphoglyceric acid. The whole process takes place only in mesophyll cells.

What are the Similarities Between C4 and CAM Plants?

• C4 plants and CAM plants are present in the environments that have low water availability.
• Also, mesophyll cells are involved in both C4 and CAM carbon fixation pathways.

What is the Difference Between C4 and CAM Plants?

C4 and CAM plants are two types of plants that carry out two different photosynthetic pathways that differ from the C3 photosynthesis. C4 plants carry out C4 photosynthesis while CAM plants carry out CAM photosynthesis. Hence, this is the key difference between C4 and CAM plants. C4 plants are mainly mesophytic while CAM plants are xerophytic. Therefore, it is another difference between C4 and CAM plants.

Furthermore, the first carbon product of the C4 plants is oxaloacetate while the first carbon products of CAM plants are oxaloacetates at night and PGA at day time. Therefore, we can consider this also as a difference between C4 and CAM plants. CAM plants can store CO₂ at night, unlike C4 plants. Moreover, CAM plants can store water as well, unlike C4 plants.

Besides, C4 plants show Kranz anatomy while CAM plants do not show Kranz anatomy. Also, in C4 plants, carbon fixation occurs in both mesophyll cells and bundle sheath cells while in CAM plants, carbon fixation occurs only in mesophyll cells. So, this is one more difference between C4 and CAM plants.

The below is an infographic on the difference between C4 and CAM plants.

Summary – C4 vs. CAM Plants

C4 and CAM plants are present in arid environments. Therefore, they utilize special carbon fixation pathways to fix carbon and also to preserve the water content in the plant body. CAM plants are a type of plants which utilize CAM photosynthesis. C4 plants are the type of plants that produce a 4-carbon compound; oxaloacetate as the first stable product of carbon fixation process. The key difference between C4 and CAM plants is that in C4 plants, carbon fixation takes place in both mesophylls (by PEP), and bundle sheath cells (by rubisco) while in CAM plants carbon fixation takes place only in mesophyll cells.

Reference:

1. “C3, C4, And CAM Plants.” Khan Academy, Khan Academy. Available here 
2. “C4 Plants: Definition, Types & Examples.” Study.com, Study.com. Available here  

Image Courtesy:

1.”Cross section of agave, a CAM plant”By Ninghui Shi – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.”Cross section of maize, a C4 plant”By Ninghui Shi – Own work, (CC BY-SA 3.0) via Commons Wikimedia