Change in the Phytohormonal Status of Japanese Red Pine after the Fukushima Accident

After the accident at the Fukushima Daiichi Nuclear Power Plant, an increased frequency of cancellation of the apical dominance has been revealed in young pine trees. The detected morphoses are most likely to result from radiation damage to the apical meristems of the conifers and also from changes in their phytohormonal status. To test this hypothesis, we have checked Japanese red pine populations from areas contaminated with radionuclides after the Fukushima accident for the frequency of morphoses related to cancellation of the apical dominance and estimated the content of main phytohormone classes: indoleacetic acid (IAA), indolylbutyric acid (IBA), zeatin, gibberellic acid (GA), and abscisic acid (ABA). The concentrations of phytohormones in the needles of young trees (5–8 years) were determined by high performance liquid chromatography. It has been shown for the first time that chronic radiation exposure changes the ratio of the main phytohormone classes in the needles of Japanese red pine: the concentrations of IAA, zeatin, and ABA increase, while the concentrations of GA decreases. The results have allowed us to explain the phenomenon of the increased frequency of cancellation of the apical dominance in the populations of young conifer trees from the zone of the Fukushima accident.