C-4 Pathway in <Emphasis Type="Italic">Pennisetum purpureum</Emphasis>

HIGH rates of photosynthesis and low rates of photorespiration are found in several plant species in which the photosynthetic carbon reduction (PCR) cycle is augmented by a second carboxylation system, the C-4 pathway^1,2. This pathway does not result in a net fixation or reduction of carbon, but seems to operate as a mechanism for concentrating CO₂ at the site of reductive assimilation. It has been widely accepted that the carboxylation reaction of the C-4 pathway is associated with the chloroplasts of mesophyll -cells, while PCR cycle activity is restricted to the bundle sheath chloroplasts. Investigations^3–5 indicate, however that mesophyll chloroplasts do contain PCR cycle activity, arni that the C-4 pathway is located in the cytoplasm of non-green and mesophyll cells.