Photosynthesis by the pericarp of developing cereal grain

• Main Author: Nutbeam, Anthony Roger
• Published: University of Edinburgh 1979
• Subjects: 571.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660124

Some photosynthetic properties of the chlorophyll containing layers of the immature cereal pericarp are described. The tissue was found to be capable of high rates of photosynthesis as determined by light dependent oxygen evolution. These rates were, however, reduced when isolated pericarps were used. The activity and kinetic properties of the enzyme phosphoenol pyruvate carboxylase (DC 4.1.1.31) were investigated in some detail. In general enzyme activity followed chlorophyll content of the pericarp, although these results depended upon the exact conditions of plant growth. The dependence of enzyme activity on phosphoenol pyruvate and glucose 6 - phosphate concentration was investigated. The kinetic properties of the barley pericarp enzyme were found to be very similar to that from the maize leaf. The pericarp was found to contain high concentration of phenols. These could be oxidised either in non-enzymic reactions by metal ions or enzymically by polyphenol oxidase. Thus extraction and reaction media were devised in which enzyme degradation by the products of phenol oxidation was minimised. The products of carbon dioxide fixation in isolated pericarps were in part identified, and resembled those reported for plants having the C4 pathway. Further, the measured enzyme activities correlated with those found in plants with this pathway. The metabolic events leading to the synthesis of phosphoenol pyruvate remain unresolved.