THE INCORPORATION OF C 14 -ADENINE AND C 14 -PHENYLALANINE BY DEVELOPING ROOT-TIP CELLS

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Abstract
The incorporation of C14-phenylalanine and C14-adenine was followed in the cells of the root tip of Allium cepa by autoradiographic techniques. The apical initials had a very low incorporation of both compounds, indicating little or no protein or RNA synthesis in this tissue. The cells in radial enlargement had a steady rate of incorporation which appears to be an indication of steady protein and RNA synthesis with time, resulting in a net increase in both as the cells are displaced from the tip. With elongation, cytoplasmic incorporation of radioactivity increases greatly, while the RNA and protein content of the cells remains constant, indicating either a greater increase of synthesis with an equally significant increase in breakdown or an exchange phenomenon associated with elongation. There is no change in nuclear or nucleolar incorporation of either radioactive compound with elongation. Cytoplasmic incorporation of C14-adenine is higher when mitosis occurs, while the incorporation of C14-pheaylalanine is unaffected by cell division. Nuclear and nucleolar incorporation of C14-phenylalanine is much higher during mitosis while C14-adenine incorporation is not affected. Treatment of the roots with RNA-ase before incorporation of the radioactive compounds resulted in a significant effect on C14-phenylalanine incorporation by the cytoplasm but not on nuclear incorporation.