Difference Between Mesophyll and Bundle Sheath Cells

The key difference between mesophyll and bundle sheath cells is that in C4 plants, light-dependent reactions of photosynthesis take place in the mesophyll cells, while light-independent reactions or Calvin cycle take place in the bundle sheath cells.

C4 plants are a group of plants that carry out C4 photosynthesis or C4 carbon fixation. These plants are able to minimize photorespiration by separating initial CO2 fixation and the Calvin cycle in space. In order to do this, they have a special cell arrangement called Kranz leaf anatomy. In Kranz anatomy, each vascular bundle is surrounded by bundle sheath cells. Mesophyll cells then surround bundle sheath cells.

Mesophyll and bundle sheath cells have structurally and functionally different chloroplasts. Mesophyll cells possess thin cell walls and randomly arranged chloroplasts with stacked thylakoids. They do not have starch granules. On the other hand, bundle sheath cells have thick cell walls and centrifugally arranged chloroplasts with large starch granules.

CONTENTS

1. Overview and Key Difference
2. What are Mesophyll Cells
3. What are Bundle Sheath Cells
4. Similarities Between Mesophyll and Bundle Sheath Cells
5. Side by Side Comparison – Mesophyll vs Bundle Sheath Cells in Tabular Form
6. Summary

What are Mesophyll Cells?

Mesophyll cells are ground tissues found in plant leaves. Their primary role is photosynthesis. There are two distinct types of mesophyll cells in leaves. They are palisade parenchyma and spongy parenchyma. Both types of cells have chloroplasts and appear in green colour. Palisade parenchyma is the upper ground tissue present in the plant leaves. It is located just below the upper epidermis of dorsiventral leaves. It consists of columnar shaped cells. The cells are tightly packed without intercellular spaces. Spongy parenchyma is the lower and second ground tissue in plant leaves. It is located below the palisade parenchyma, towards the lower epidermis. Spongy parenchyma cells are loosely arranged; hence, there are a lot of intercellular spaces between cells. The cells are oval-shaped or irregular shaped.

In C4 plants, mesophyll cells are differentiated to carry out only light dependant reactions of photosynthesis in order to minimize photorespiration. Therefore, mesophyll cells of C4 plant leaves are seen surrounding the bundle sheath cells. They have thin cell walls and randomly arranged chloroplasts. Moreover, mesophyll cells have stacked thylakoids and little or no starch granules.

What are Bundle Sheath Cells?

Bundle sheath cells are special types of cells seen in C4 plant leaves. They are seen around leaf veins surrounding the vascular bundles. The light-independent reactions of photosynthesis or the Calvin cycle take place in bundle sheath cells. Rubisco enzyme in bundle sheath cells fix CO2 and produce sugars.

Bundle sheath cells have thick cell walls. Moreover, they have centrifugally arranged chloroplasts. They have starch granules and unstacked thylakoid membranes.

What are the Similarities Between Mesophyll and Bundle Sheath Cells?

• Both mesophyll and bundle sheath cells are living plant cells.
• They are found in C4 plant leaves.
• Both types of cells are differentiated cells.
• They are in direct contact with each other.
• Moreover, both types of cells have chloroplasts and chlorophylls, and they participate in photosynthesis.
• There is a division of labour between mesophyll and bundle sheath cells in C4 plants.

What is the Difference Between Mesophyll and Bundle Sheath Cells?

Mesophyll cells are the cells in C4 plants that carry out light dependant reactions of photosynthesis. In contrast, bundle sheath cells are the cells surrounding the leaf veins of C4 plants that carry out light-independent reactions. So, this is the key difference between mesophyll and bundle sheath cells. Also, another difference between mesophyll and bundle sheath cells is that mesophyll cells carry out the light reaction in C4 plants, while bundle sheath cells carry out the dark reaction in C4 plants.

Moreover, mesophyll cells are present in the middle of the leaf around the bundle sheath cells, while bundle sheath cells are present surrounding the leaf veins. Besides, structurally, mesophyll cells have thin cell walls while bundle sheath cells have thick cell walls.

The below infographic summarizes the difference between mesophyll and bundle sheath cells.

Summary – Mesophyll vs Bundle Sheath Cells

In C4 plants, both mesophyll and bundle sheath cells are photosynthetic tissues. Mesophyll cells are present in the middle of the leaf surrounding the bundle sheath cells. The light-dependent reaction takes place in mesophyll cells in C4 plants. On the other hand, bundle sheath cells surround leaf veins or vascular bundles of C4 plants. The light-independent reaction takes place in bundle sheath cells. So, this is the summary of the difference between mesophyll and bundle sheath cells.

Reference:

1. “C3, C4, And CAM Plants (Article).” Khan Academy, Khan Academy, Available here.
2. “C4 Carbon Fixation.” Wikipedia, Wikimedia Foundation, 23 Feb. 2020, Available here.

Image Courtesy:

1. “C4 Plant Anatomy”  By Adam Schwendt – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Angiosperm Morphology Bundle Sheaths in Zea Leaf (36808119403)” By Berkshire Community College Bioscience Image Library – Angiosperm Morphology: Bundle Sheaths in Zea Leaf (CC0) via Commons Wikimedia