Non-Autotrophic Carbon Dioxide Metabolism in Cacti

Non-autotrophic ("dark") 14CO2 metabolism and associated acid accumulation were studied in the Cactaceae. Carbon dioxide assimilation and oxygen uptake were generally lower than in crassulacean succulents. The primary products were organic acids (malic acid) and amino acids. Little or no 14C activity was detected in lipoidal or neutral components. After a 2-hr dark CO2 fixation period, the first-order rate constant for steady-state...