The regulation of pollen tube growth in Douglas-fir following high doses of ionizing radiation.

Acute irradiation of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) pollen by X-rays enhances pollen tube elongation. To determine whether this effect was due to physical damage of the pollen membranes or to metabolic processes, irradiated and control pollen were grown under conditions of anoxia. Thus, it was determined that physical damage only could be of minor importance. As parameters for metabolic processes RNA- and protein synthesis were studied. The only difference between irradiated and control pollen with respect to RNA synthesis was the time at which it started. Protein synthesis in vitro revealed that polyribosomes from irradiated pollen were more active than those from control pollen at lower concentrations. These results were confirmed by in ovo experiments with both polysomal preparations. The results indicate that X-ray irradiation is interfering with the main regulatory mechanism of pollen tube growth, which is de- and re-masking of, mainly, presynthesized mRNA.