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

Abstract

The formation of lignin in wheat plants from C14O2 during the period of rapid lignifica-tion, has been studied over the 1st few hrs. of photosynthesis by measuring the incorporation of C14 into the guaiacyl and syringyl portions of the lignin molecule. Plants grown 62 days from seeding were exposed to 20 microcuries of C14O2 in a closed chamber for 20 min., and grown for periods of 1 to 24 hrs. in a normal atmosphere before harvesting. Synthesis of lignin is most rapid 4 to 6 hrs. from activation, the syringyl residues apparently being formed more slowly than the guaiacyl. A slower rate of formation persists for the remainder of a 1-day period, probably as a result of recycling in the carbon pool. Cellulose acquires C14 more rapidly than lignin during the period immediately following administration of C14O2 but after 3 or 4 hrs. when synthesis of lignin has become rapid, the total C14 content of both components reaches about the same value.