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)-³H after incubation with thymidine-³H in the presence of millimolar deoxyadenosine. Most of this dTTP-³H 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-³H 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-³H, 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.