Simultaneous occurrence of C₃ and C₄ photosyntheses in relation to leaf position in Mollugo nudicaulis

Abstract

Since the discovery of C₄ photosynthesis higher plants have been categorised into C₃ plants, which form 3-phosphoglycerate (PGA) as the first labelled intermediate, and C₄ plants, which form 4-carbon acids as the predominant early photosynthetic products, C₄ plants can also be distinguished by features such as Kranz leaf anatomy, low photorespiration, high photosynthetic efficiency and reduced ¹³C discrimination. Although 943 C₄ plants are known to be distributed among 18 families, only 18 genera from 10 families include both C₃ and C₄ plants. Kennedy and Laetsch described Mollugo verticillata as intermediate for C₃ and C₄ photosynthesis. But Brown and Brown felt that it was a typical C₃ plant. Recently three Panicum species (P. milioides, P. hians and P. laxum) have been found to have photosynthetic characteristics intermediate between C₃ and C₄ plants. We now report that a single plant of Mollugo nudicaulis can have some leaves with C₃ characteristics and others with C₄ characteristics according to their position on the stem.