AUTORADIOGRAPHIC STUDY OF RNA SYNTHESIS DURING SECONDARY RHIZOID CELL DIFFERENTIATION IN PTERIS VITTATA

Abstract

The pre‐ and postmitotic stages of rhizoid cell differentiation in Pteris vittata L. were pulsed in radioactive uridine for 30 min and the data analyzed quantitatively by autoradiography. The total grain count rises from 594 in the nondifferentiating cell to 1,369 in the corona stage; increases to 2,745 in the internally segmented rhizoid cell (IRC) and to 2,779 in the wheel; and then drops to 1,306 in the protrusion and to 1,261 in the early rhizoid. The significant increase in nucleolar labeling in the corona reflects an increase in ribosomal RNA synthesis for mitosis‐associated syntheses. The two‐fold increase in grains over the cellular compartments of the IRC and wheel reflects an increase in RNA synthesis in these postmitotic stages. The similarity of labeling profiles between these stages suggests that they are not far enough separated to show a difference in their roles. The decline in total grain counts in the protrusion and early rhizoid stages to half the maximum levels suggests that an overall decrease in RNA synthesis is attended by a shift from a differentiating phase to a steady‐state growth system.