FACTORS AFFECTING DEVELOPMENT OF PEROXISOMES AND GLYCOLATE METABOLISMAMONG ALGAE OF DIFFERENT EVOLUTIONARY LINES OF THE PRASINOPHYCEAE

Leaf-type peroxisomes are not present in the primitive unicellular Pra sinophycean line of algae but are present in the multicellular algae M ougeotia, Chara, and Nitella, which are in the one evolutionary line, Charophyceae, that led to higher plants. Processes related to glycolat e metabolism that may have been modified or induced with the appearanc e of peroxisomes have been examined. The algal dissolved inorganic car bon-concentrating mechanism and alkalization of the medium during phot osynthesis were not lost when peroxisomes appeared in the members of t he Charophycean line of algae. Therefore, it is unlikely that lowering of the CO2 concentration in the environment was a major factor in the evolutionary appearance of peroxisomes. Multicellular Mougeotia, earl y members of the Charophycean line of algae, have peroxisomes, but the y excrete excess glycolate into the medium. The cytosolic pyruvate red uctase for D-lactate synthesis and the glycolate dehydrogenase activit y almost disappeared when peroxisomal glycolate oxidase, which also ox idizes L-lactate, appeared. These biochemical changes do not indicate what caused the induction of leaf-type peroxisomes in this evolutionar y line of algae. The oxygenase activity of ribulose-1,5-bisphosphate c arboxylase/oxygenase and glycolate oxidase require about 200 to 400 mu M O-2 for 0.5 V-max. These high-O-2-requiring steps in glycolate meta bolism would have functioned faster with increasing atmospheric O-2, w hich might have been the causative factor in the induction of peroxiso mes.