The isolation and characterization of mutants of the C4 photosynthetic pathway

Abstract

Three novel classes of the C₄ plant Amaranthus edulis are described. (1) A mutant that contains less than 10% of the normal activity and protein of phosphoenol-pyruvate carboxylase. (2) A mutant that is deficient in NAD-malic enzyme activity, but contains the normal two subunits of the enzyme protein. (3) Four mutant plants that accumulate high concentrations of glycine following exposure to air. A common characteristic of all the mutant plants is that they grow poorly in air and exhibit very low rates of photosynthetic CO₂ assimilation. The characteristics of the mutant lines are discussed with reference to our current knowledge of the regulation of the C₄ photosynthesis pathway. The possibility that C₄ plants undergo photorespiratory nitrogen and carbon metabolism when grown in air is considered in detail.