RuBisCo is
an enzyme that acts both as a carboxylase and oxygenase. Why do you
think RuBisCo carries out more carboxylation in C4
plants?
RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C4 plants?
The enzyme
RuBisCo is absent from the mesophyll cells of C4 plants.
It is present in the bundle-sheath cells surrounding the vascular
bundles. In C4 plants, the Calvin cycle occurs in the
bundle-sheath cells. The primary CO2 acceptor in the
mesophyll cells is phosphoenol pyruvate – a three-carbon
compound. It is converted into the four-carbon compound oxaloacetic
acid (OAA). OAA is further converted into malic acid. Malic acid is
transported to the bundle-sheath cells, where it undergoes
decarboxylation and CO2 fixation occurs by the Calvin
cycle. This prevents the enzyme RuBisCo from acting as an oxygenase.
The enzyme RuBisCo is absent from the mesophyll cells of C4 plants. It is present in the bundle-sheath cells surrounding the vascular bundles. In C4 plants, the Calvin cycle occurs in the bundle-sheath cells. The primary CO2 acceptor in the mesophyll cells is phosphoenol pyruvate – a three-carbon compound. It is converted into the four-carbon compound oxaloacetic acid (OAA). OAA is further converted into malic acid. Malic acid is transported to the bundle-sheath cells, where it undergoes decarboxylation and CO2 fixation occurs by the Calvin cycle. This prevents the enzyme RuBisCo from acting as an oxygenase.
