Intake of Radionuclides in the Trees of Fukushima Forests 4. Binding of Radioiodine to Xyloglucan

Abstract

The 1,4-linked glucans such as xyloglucan and amylose are known to form a complex with iodine/iodide ions and to also be precipitated with CaCl2 in the presence of iodine. Here, we show that iodine gas could be specifically incorporated into xyloglucan. Furthermore, we show that [125I]I2 gas is, over time, incorporated at high levels into the entire outer surface of poplar seedlings but that spraying seedlings with abscisic acid to close stomata decreases the incorporation of the gas. There was less incorporation of the gas in a transgenic poplar overexpressing xyloglucanase at the early stages when compared with a wild type. This shows that xyloglucan serves as a key absorber of iodine gas into a plant body. After individual leaves of cultured seedlings were exposed to the gas for 30 min, no radioiodine was emitted from those leaves over the following two weeks, indicating that no turnover occurs in radioiodine once it is bound to the polysaccharides in plant tissues. We conclude that forest trees could serve as one of the largest enormous capture systems for the radioiodine fallout following the nuclear power plant accident in Fukushima.

Intake of Radionuclides in the Trees of Fukushima Forests 5. Earthquake Could Have Caused an Increase in Xyloglucan in Trees

“…Here, we showed that radioiodine-targeted xyloglucan was elevated in the annual rings of forest trees after a megathrust earthquake (Figure 2). Therefore, we conclude that the increased xyloglucan signals that we observed in the growth rings of forest tree trunks in the wild were likely caused, at least in part, by earthquakes, different from the intake of radionuclide in the trees due to the accident involving a nuclear power plant [1][2][3][4]. The 2011 megathrust earthquake not only triggered a nuclear power plant accident that dispersed radioiodine, which then became bound to xyloglucan in trees as an artificial event due to a human error, but also increased xyloglucan signaling in annual rings of forest trees as a plant response against seismic stress under natural phenomena.…”

“…The earthquake and tsunami on 11 March 2011 led to a meltdown followed by a hydrogen explosion at the Fukushima-Daiichi nuclear power plant in Japan, causing the dispersal of abundant radionuclides into forests and local residences by gaseous or aerosol forms [1][2][3][4]. Radioiodine and radiocesium were likely incorporated and fixed in forest trees.…”