Radioisotopic studies of DNA biosynthesis in relation to growth of Zea mays roots

Abstract

Root growth consists of two basic processes, cell division and cell elongation. An integral part of the first process is the synthesis of deoxyribonucleic acid (DNA). DNA biosynthesis was studied in primary roots of Zea mays through incorporation of ³H-thymidine by autoradiography and liquid scintillation spectrometry. DNA synthesis was restricted to the meristematic region of the primary root. The curve representing this process was bell-shaped with a peak at 1.5 mm from the tip. Up to 3 mm distance from the tip, the root was growing both by cell division and cell elongation. This was also the region of DNA synthesis. The root region between 3 to 9 mm from the tip. was growing only by cell elongation. The relative elemental rate of elongation had a maximum at 3.5 mm from the tip, or shortly after cessation of DNA synthesis and cell division. Cells stopped elongating at 9 mm distance from the tip.