Looking for classes? Ksquare Career Institute, Bengaluru →
In the leaves of $C_4$ plants, malic acid formation during $CO_2$ fixation occurs in the cells of
A
bundle sheath
B
phloem
C
epidermis
D
mesophyll
Detailed Solution
The leaves of $C_4$ plants show Kranz anatomy, with mesophyll cells and large bundle sheath cells around the vascular bundles.
In $C_4$ plants the $C_4$ cycle occurs in the mesophyll cells and the $C_3$ (Calvin) cycle occurs in the bundle sheath cells.
The primary $CO_2$ acceptor, phosphoenol pyruvate (PEP), is present in the mesophyll cells, where the enzyme PEP carboxylase fixes $CO_2$ to form oxaloacetic acid (OAA).
OAA is then reduced to malic acid (or converted to aspartic acid) in the mesophyll cells themselves.
The malic acid is transported to the bundle sheath cells, where it is broken down to release $CO_2$ for the Calvin cycle.
So malic acid formation occurs in the mesophyll cells.
In $C_4$ plants the $C_4$ cycle occurs in the mesophyll cells and the $C_3$ (Calvin) cycle occurs in the bundle sheath cells.
The primary $CO_2$ acceptor, phosphoenol pyruvate (PEP), is present in the mesophyll cells, where the enzyme PEP carboxylase fixes $CO_2$ to form oxaloacetic acid (OAA).
OAA is then reduced to malic acid (or converted to aspartic acid) in the mesophyll cells themselves.
The malic acid is transported to the bundle sheath cells, where it is broken down to release $CO_2$ for the Calvin cycle.
So malic acid formation occurs in the mesophyll cells.