Tube growth stimulation of pine pollen by low doses of irradiation. Dose rate, reproducibility and comparison between UV-light and ionizing rays.

Stimulation of the tube growth of pine pollen by low doses of UV-light or X-rays is a reproducible process, but it depends strongly of the dose rate applied. It can be proved that the observed effect is more determined by dose rate and irradiation time than by the dose itself which can vary by nearly one order of magnitude for achieving the same increase in tube elongation. The range of absorbed energy at which the stimulation effect can be observed is rather broad and overlapping between UV and X-rays. In the average the UV-energy needed is 5 times higher than X-ray energy.