Immunological Determination of Phosphoenolpyruvate Carboxylase and the Large and Small Subunits of Ribulose 1,5-Bisphosphate Carboxylase in Leaves of the C4 Plant Pearl Millet

Abstract

The light-dependent development of the photosynthetic apparatus in the 1st leaf of the C4 plant pearl millet, was monitored by immunologically determining the concentration of phosphoenolpyruvate carboxylase and ribulose 1,5-bisphosphate carboxylase. A competitive enzyme-linked immunosorbent assay procedure using antibodies to the monomeric subunit of phosphoenolypyruvate carboxylase and the large and small subunit of ribulose 1,5-bisphosphate carboxylase was used to quantitate the amounts of these polypeptides in the 1st leaf of etiolated seedlings and etiolated seedlings exposed to light for varying periods of time. Phosphoenolypyruvate carboxylase was present in etiolated tissues; light stimulated its synthesis nearly 23-fold. Maximum accumulation of phosphoenolpyruvate carboxylase occurred .apprx. 4 days after etiolated plants were placed in the light. Both the large subunit and the small subunit of ribulose 1,5 bisphosphate carboxylase were present in leaves of etiolated seedlings. Light also stimulated the synthesis of both of these polypeptides, but at different rates. In etiolated leaves there was .apprx. a 3-fold M excess of the small subunit to large subunit. Exposure of the etiolated leaves to light resulted in the molar ratio of the large subunit to the small subunit increasing to .apprx. 0.72. The net synthesis of these 2 polypeptides is not coordinately regulated at all times.