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C4 physiology is a system of interrelated developmental, anatomical, cellular
and biochemical traits that can significantly enhance photosynthetic
efficiency, water- and nitrogen-use efficiency, and other characteristics that
influence biomass or harvest yield under given environmental conditions. In C4
plants, physiology is regulated in cellular patterns in the leaf that both
increase the efficiency of inputs and eliminate sources of losses and
inhibitions. All existing species that are able to fix carbon dioxide through
one of the variety of C4 schemes appear to rely on an enhancement of enzymatic
activities and anatomical features, with an asymmetric distribution in most C4
species between leaf bundle sheath (BS) and mesophyll (M) cells. Most C4
species exhibit variations of Kranz anatomy, in which metabolically cooperating
BS and M cell types form successive layers around a dense pattern of minor,
intermediate, and major veins, although an intracellular compartmentalization
of cooperating activities has been found in a few C4 species. This inter- or
intracellular compartmentalization supports the delivery of CO2-derived carbon
to RuBisco in an environment that limits competition from oxygen and the loss
of fixed CO2.
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