BOTANY Higher Secondary Second Year - Textbooks Online

3. Malic acid or aspartic acid formed in chloroplast of mesophyll
cells is transferred to the chloroplasts of bundle sheath where it is
decarboxylated to form CO 2 and pyruvic acid in the presence of
NADP + specific malic enzyme.
4. Now, second carboxylation occurs in chloroplasts of bundle sheath
cells. Ribulose bisphosphate accepts CO 2 produced in step (3) in the
presence of RuBP carboxylase and yields 3-phosphoglyceric acid. Some
of the 3-phosphoglyceric acid molecules are utilised to produce sucrose
and starch, while remaining PGA molecules are used for the regeneration
of RuBP.
5. The pyruvic acid produced in step (3) is transferred to the chloroplasts
of mesophyll cells where it is phosphorylated to regenerate
phosphoenolpyruvic acid . This reaction is catalysed by pyruvate kinase
in the presence of Mg 2+ .
Adenylate kinase
The AMP is phosphorylated by ATP in the presence of adenylate
kinase to form 2 molecules of ADP.
C 4 plants are photosynthetically more efficient than C 3 plants, because
the net requirement of ATP and NADPH 2 for the fixation of one molecule
of CO 2 is considerably lower in C 4 plants than in C 3 plants.
186