The potential of higher plants with the phosphopyruvic acid cycle

Abstract

Optimal conditions for photosynthesis by intact higher plants are considered as those resulting in the maximum production of organic matter from carbon dioxide over a prolonged period of time. Photosynthetic yields may be limited by the ability of plants to fix and retain carbon from an atmosphere containing high concentrations of oxygen and low concentrations of carbon dioxide. In many plants photosynthetic capacity is decreased under these conditions as a result of loss of carbon from the photosynthetic carbon reduction cycle as glycollic acid. Photosynthesis is further decreased by the loss of carbon dioxide from the leaf during the further metabolism of this glycollate in photorespiratory processes. Other plants, tropical grasses in particular, are resistant to inhibition by high concentrations of oxygen. This resistance is associated with an apparent lack of photorespiration, a characteristic leaf anatomy, dimorphic chloroplasts and an ancillary mechanism for trapping carbon dioxide— the phosphopyruvic acid cycle. It is concluded that a tropical grass such as sugar cane could produce the optimum yield of organic material in an artificial environment.