Transgenic Flaveria bidentis
C4 plants are a group of relatively recently evolved angiosperms which are represented in a large number of both monocot and dicot genera (see Hatch 1987, 1992). C4 plants are of agricultural importance not only because they are strongly represented among tropical and subtropical crop species (maize, sorghum, sugarcane, and amaranth, for example, are C4), but also because of their acknowledged role as some of the world’orst weeds. C4 plants are so named because they initially fix atmospheric CO2 via phosphoenolpyruvate carboxylase to form the C4 acid oxaloacetate (Fig. 1; Hatch 1987). This C4 acid is converted to either aspartate or malate and transported to the bundle sheath cells, where it is decarboxylated to produce CO2, the substrate for Rubisco (Fig. 1). The C4 mechanism operates as a biochemical pump which concentrates CO2 at the site of Rubisco to levels up to ten times atmospheric. This high CO2 concentration means that Rubisco is operating at saturating CO2 in ambient air and photorespiration is almost totally suppressed. This has important implications for the efficiency of photosynthesis in air at higher temperatures and also improves the water use efficiency of C4 plants. Consequently, most C4 plants thrive under warmer and often more arid environments.
KeywordsBundle Sheath Sheath Cell Phosphoenolpyruvate Carboxylase Bundle Sheath Cell Orthophosphate Dikinase
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