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C4 Leaf Anatomy-2

WB01338_2.gif (869 bytes) There are two types of Chloroplasts in the Mesophyll versus the Bundle Sheath cells of C4 Leaves.

Typical Chloroplasts with Grana are observed in Mesophyll Cells.

However, Chloroplasts without Grana (Agranal) are found in the Bundle Sheath cells.

The Bundle Sheath Plastids usually contain a lot of Starch while the Mesophyll Plastids have little Starch.


WB01338_1.gif (869 bytes) Small Vascular Bundle from Sugarcane (C4) leaf. The Yellow square labeled TEM is shown on the Right. The Mesophyll Cells are colored green in the TEM photos.


Note the differences between the Chloroplasts in the Bundle Sheath compared to the Mesophyll which have grana while the Bundle Sheath Plastids are Agranal and contain Starch.

TEM image of a Bundle Sheath Cell: Note the many Chloroplasts which contain Starch (See below.)


TEM image of Mesophyll Cells: Note the many Grana and the relative absence of Starch in these Chloroplasts.


Bundle Sheath Chloroplast containing lots of Starch


Mesophyll Chloroplast with many Grana and small Starch deposits

WB01338_1.gif (869 bytes) Starch accumulates in the Bundle Sheath Chloroplasts during active periods of photosynthesis. Most of it is transported to the Phloem during the night.

Small amounts of starch occur in Mesophyll Cell Chloroplasts during Photosynthesis but most of the CO2 fixation occurs in the Bundle Sheath Chloroplasts and that is why most of the Starch is deposited there.

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