DISTRIBUTIONS OF GROWTH, NUCLEIC ACIDS, AND NUCLEIC‐ACID SYNTHESIS IN SEEDLING ROOTS OF ZEA MAYS

Abstract

W oodstock , L owell W., and F olke S koog . (U. Wisconsin, Madison.) Distributions of growth, nucleic acids, and nucleic‐acid synthesis in seedling roots of Zea mays . Amer. Jour. Bot. 49(6): 623–633. Illus. 1962.—The rate of growth of each of 6 inbred lines of Zea mays was shown earlier to be directly proportional to the amount of ribonucleic acid (RNA) in the apex. In the present communication, 2 of these lines, W–58 and W–148, have been studied with respect to the distribution of growth and RNA in a further attempt to elucidate the relationship between cell elongation and RNA. Two‐day‐old W–58 roots grew 1.01 mm/hr, had a growing region of 9.0 mm, and a maximum relative elemental rate of elongation of 0.23 mm/hr/mm. Two‐day‐old W–148 roots grew 1.56 mm/hr, had a growing region of 11.0 mm, and a maximum relative elemental rate of elongation of 0.26 mm/hr/mm. In W–58, rapid RNA synthesis occurred over the apical 2.0 mm and the maximum level was 1.40 × 10 ‐4 μg RNA/cell. In W–148, rapid RNA synthesis occurred over the first 4.0 mm to give a maximum level of 2.34 × 10 ‐4 μg RNA/cell. Fresh weights per cell increased to 122 × 10 ‐6 mg in W–58 and to 160–190 × 10 ‐6 mg in W–148. The estimated duration of rapid cell elongation of an individual cell was 13.9 hr in W–58 and 13.4 hr in W–148. The results are in agreement with the hypothesis that the amount of RNA synthesis by the cells while still in the apex determines their subsequent rate of elongation as well as their final size.