Localisation of the site of action of tube growth stimulation by micro UV-irradiation of pine pollen.

Micro-irradiation of pine pollen grains was carried out with different doses at four different dose rates and the tube growth was observed. The irradiation of the whole pollen grains in the dehydrated state and dorsal position and of those in the hydrated state and ventral position induced stimulated tube growth after receiving low doses of UV light. The effect of stimulation depended on the ratio between dose and dose rate. After partial irradiation of pollen grains at low doses, carried out with the technique of "blind shot", a stimulation effect could also be observed. It was calculated that the irradiation of the cytoplasm had a strong, the irradiation of the active nucleus (vegetative) had a moderate and the irradiation of the dormant nucleus (generative) had little or no dose rate dependance. The dose effect of the nuclei showed a reverse tendency to the dose effect of the cytoplasm. Experiments with different light filters suggested that the dose rate dependence of the cytoplasm is probably not caused by a repair mechanism. The vegetative nucleus showed an effect of photoreactivation and probably also of a dark repair. The generative nucleus exhibited only an effect of photoreactivation.