Yoshida - 1981 - Fundamentals of Rice Crop Science

196 FUNDAMENTALS OF RICE CROP SCIENCE
This reaction does not require light and can proceed in darkness.
Carbon dioxide is converted into carbohydrates during photosynthesis by two
biochemical processes: C-3 and C-4 pathways (Hatch and Slack 1970, Bjorkman
and Berry 1973). In the C-3 pathway, which is often called the Calvin Cycle,
carbon dioxide is first incorporated into 3-phosphoglycerate (PGA):
Note that the carbon atom in the CO 2 molecule (marked with an asterisk) is
incorporated into the carboxyl group of one PGA molecule. In subsequent reactions,
some PGA is converted into carbohydrates and some is used to regenerate
RuDP molecules to serve as CO 2 acceptors. PGA is a compound with three carbon
atoms per molecule; hence, the pathway is named the three-carbon photosynthetic
pathway (C-3 pathway).
In the C-4 pathway, CO 2 is first incorporated into compounds with four carbon
atoms:
+ P (5.5)
CO 2 fixation and the formation of C-4 acids, malate and aspartate, occur in the
mesophyll cells. The C-4 acids, transported to inner bundle sheath cells, are
converted into CO 2 and pyruvate (C-3 compound):
(5.6)
The released CO 2 is fixed again in the Calvin cycle to produce PGA and carbohydrate.
The pyruvate returns to the mesophyll cells, where it acquires a phosphate