Radioautographic Localization of Deoxythymidine Triphosphate in Tradescantia Pollen Grains during Dna Synthesis

Tradescantia pollen grains, isolated during the period of DNA synthesis in the generative cell, accumulate deoxythymidine triphosphate (dTTP)-(3)H after incubation with thymidine-(3)H in the presence of millimolar deoxyadenosine. Most of this dTTP-(3)H was found to resist extraction by the fixative, cold ethanol-acetic acid, and its location was investigated by radioautography with thin, dry emulsion. Substantial binding of dTTP-(3)H occurred as an artifact; but when nuclei were isolated from the fixed pollen grains by sonication, it was found that they were differentially labeled: generative nuclei contained dTTP-(3)H, vegetative nuclei did not. This observation is discussed and is interpreted as evidence supporting the idea that thymidine is phosphorylated only in the generative cell of the pollen grain.