Abstract
Zeatin and zeatin-9, β-ribonucleoside enhance the germination of dormant ash embryos. While the first macroscopic signs of germination appear only after about 72 hours, 12 hours of exposure to 50 μm zeatin is as effective as continuous incubation. There must be barriers against transport out of the embryos since 8-14C-zeatin and its metabolites, zeatin-9, β-ribonucleoside, the 5′-mono and the suspected di- and triphosphates, accumulate against a concentration gradient. Zeatin ribonucleoside is about as effective as zeatin in enhancing embryo germination, yet the internal 8-14C-zeatin level is lower by a factor of about 50 when the ribonucleoside is fed. The physiological effects of zeatin and abscisic acid on the germination of ash embryos are antagonistic. There is, however, no evidence that abscisic acid has a significant effect on 8-14C-zeatin uptake or conversions.
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