The effect of electron acceptors on the phytochrome-controlled germination of Paulownia tomentosa seeds.
The effect of substances with different redox potentials on the phytochrome-controlled germination of Paulownia tomentosa seeds was examined. Up to 25% of water-imbibed seeds germinated upon irradiation with 5 min red light. Up to 80% germination was observed for seeds irradiated with 5 min red light and incubated in potassium nitrate, potassium hexacyanoferrate (III) or potassium hexachloroiridate (IV) and sodium nitroprusside. The optimum concentration was between 1 and 10 msmallcap˜M. Other electron acceptors such as 2,6-dichlorophenol-indophenol, phenazine methosulfate and methylene blue failed to produce any effect. The effectiveness of all these compounds is discussed in relation to their redox potential. The germination-promoting effect was obtained when the substances were supplied to the incubation medium from the onset of imbibition or at the onset of irradiation. Delay of application of these chemicals until after the red light treatment diminished their effectiveness and the effect was lost after 48 h. The escape from far-red reversibility was evident in the presence of substances which stimulated germination. The results presented support the view that phytochrome-broken dormancy of P. tomentosa seeds is closely connected with redox changes.