Photosynthesis in c(4) plant tissue cultures: significance of kranz anatomy to c(4) Acid metabolism in c(4) plants

The pattern of photosynthetic carbon metabolism was determined in tissue cultures of Portulaca oleracea. Four-carbon acids are the most heavily labeled photosynthetic products during short term exposure to ¹⁴CO₂, containing greater than 40% of the total radioactivity incorporated. Phosphoglyceric acid and sugars account for only 10% of the label after equal exposure times. Other features of the CO₂ assimilation pattern in Portulaca callus tissue include a relatively large percentage of label located in various minor products throughout the time course studied, and a greater incorporation of ¹⁴C into sugars in tissue cultures than occurs in leaves. Ultrastructurally, the chloroplasts and cells of the callus are like those in the mesophyll cells of Portulaca leaves. The requirement for Kranz anatomy for operation of functional C₄ physiology is discussed.