Compartmentation of Terpenoid Biosynthesis in Green Plants

On the basis of radioisotope-incorporation experiments it is suggested that acetyl-CoA, an obligatory intermediate in chloroplast terpenoid biosynthesis, may be formed inmaize from photosynthetically fixed carbon dioxide by the route carbon dioxide --> glycollate -÷ glyoxylate -* glycine --serine --> pyruvate -acetyl-CoA. The proposed route is supported by conventional radioisotope-dilution studies and by experiments with inhibitors affecting reactions involved in the pathway. The proposed route appears to play little part in formation of extrachloroplastidic sterol.