Quantitative Studies of Nucleic Acids in Contrasting Zones of Tissue Differentiation in Germinating Mimosa Seedlings

Abstract

Groups of germinating mimosa seedlings (Albizzia julibrissin Durazzini) were harvested at 3, 5, 7, and 9 days from planting. Five-millimeter root tips, second 5-mm root sections, and epicotyls were used at each age for quantitative ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) determinations. Base ratios of the RNA extracts were also determined. A comprehensive statistical analysis was run using all of the data. Epicotyl dry weight and epicotyl RNA per seedling section both increased significantly with age. In the epicotyl, DNA per seedling section and the RNA/DNA ratios increased significantly with age. Five-millimeter root-tip dry weight, second 5-mm root-section dry weight, and epicotyl DNA per unit dry weight all decreased significantly with age. Curvilinear trends were found for 5-mm root-tip RNA per unit dry weight with a peak at 7 days and for 5-mm root-tip RNA/DNA ratios with a peak at 6 days. RNA and DNA per unit dry weight, RNA and DNA per seedling section, and RNA/DNA ratios varied significantly between types of seedling sections. Individual base quantities differed significantly within each RNA extract, and base ratios varied between types of seedling sections. Only the base ratios of the second 5-mm root sections, when compared to the other two seedling sections, contributed to the difference between types of seedling sections. No significant linear or curvilinear associations were found between base ratios and seedling ages. Microscopic slide sections were made for examination of each of the two root segments. Zones of division, elongation, and differentiation and maturation were located in order to relate base ratios with the degree of differentiation of tissues. It was concluded that RNA base ratios differed between types of seedling sections, probably depending upon the degree of differentiation occurring within each section.