STUDIES OF LIGNIN BIOSYNTHESIS USING ISOTOPIC CARBON: II. SHORT-TERM EXPERIMENTS WITH C¹⁴O₂

Abstract

The formation of lignin in wheat plants from C 14 O 2 , during the period of rapid lignification, has been studied over the first few hours of photosynthesis by measuring the incorporation of carbon-14 into the guaiacyl and syringyl portions of the lignin molecule. Plants grown 62 days from seeding were exposed to 20 microcuries of C 14 O 2 in a closed chamber for 20 min., and grown for periods of 1 to 24 hr. in a normal atmosphere before harvesting. Synthesis of lignin is most rapid four to six hours from activation, the syringyl residues apparently being formed more slowly than the guaiacyl. A slower rate of formation persists for the remainder of a one-day period, probably as a result of recycling in the carbon pool. Cellulose acquires carbon-14 more rapidly than lignin during the period immediately following administration of C 14 O 2 , but after three or four hours when synthesis of lignin has become rapid, the total carbon-14 content of both components reaches about the same value.