Photosynthesis in C 4 Plant Tissue Cultures

Abstract

sue cultures of Portulaca oleracea. Four-carbon adds are the most heavily lbeled photosynthetic products during short term exposure to The pattern of photosynthetic carbon metabolism was determined in 14CO2, containing greater than 40% of the total radioactivity incorpo- rated. Phosphoglyceric acid and sugars account for only 10% of the label after equal exposure times. Other features of the CO2 assimiation pattern in Portulaca caUus tissue indude 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 tissoe cultures than occurs in leaves. Ultrastructurafly, 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 physiol- ogy is discussed.