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

A megathrust earthquake caused the Fukushima–Daiichi nuclear power plant accident, which dispersed abundant radioiodines, causing them to be bound to xyloglucan into forest trees. Nevertheless, targeted xyloglucan was found in increased quantities in the annual rings of forest trees affected by the earthquake. We propose that trees could acclimate rapidly to shaking stress through an increase in xyloglucan deposition as a plant response under natural phenomena

Intake of Radionuclides in the Trees of Fukushima Forests 3. Removal of Radiocesium from Stem Wood, Cryptomeria Japonica (L.f.) D. Don.

Nuclear power plant accidents have dispersed radiocesium into the atmosphere to contaminate trees with no turnover in heartwood, as occurred in Fukushima, and as has persisted for over 30 years around Chernobyl. Here we employ the ponding method, in which radiocesium can be flushed out from the cross-cut edges of Japanese cedar, Cryptomeria japonica (L.f.) D. Don., stem with water due to xyloglucan degradation in tracheids. Furthermore, lab-scale ponding experiments have shown that a non-detectable level of radiocesium has been observed not only in the pool water used for 575 days but also in the water containing recombinant xyloglucanase. This traditional technology is now a new biotechnology

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

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

Effect of dormancy on the development of phloem fiber clusters

The development of phloem fibers was investigated in poplars grown under artificially fixed conditions and under an artificially shortened annual cycle system that includes a dormancy phase. The phloem tissues in these trees formed two- or three-layer fiber clusters; however, clusters in trees that underwent periodic dormancy were larger than those in trees that did not. Individual fibers were also larger in the former than in the latter, as assessed on transverse sections. Differences were most pronounced in the radial diameter of fibers in the layer nearest the cambium. These results suggest that dormancy affects both the size of fiber clusters and the diameter of individual fibers. Furthermore, these results imply that dormancy affects the development of phloem fibers, and that the shortened annual cycle system is a useful model for investigating phloem development caused by dormancy repetition

Experimental Study of Intra-Ring Anatomical Variation in <i>Populus alba</i> L. with Respect to Changes in Temperature and Day-Length Conditions

There are various studies on annual ring structural variations in plants grown in the field under varying meteorological statistics. However, related experimental approach is limited, hitherto. In this study, complete artificial conditions with growth chambers were adopted to evaluate the influence of day length and temperature on intra-ring structure formation. The basic artificial growing conditions have been previously reported as “shortened annual cycle system”, which consisted of the following three stages mimicking seasons approximately: Stage 1, spring/summer; Stage 2, autumn; and Stage 3, winter. This system shortens an annual cycle of Populus alba to 5 months. In this study, Stage 2 was modified in two ways: one was a condition in which the temperature was fixed and the day length was gradually shortened, and the other was a condition with a fixed day length and gradually lowered temperature. In the former condition, the cell wall of fibers thickened from the middle of the ring, and the vessel diameter became smaller from the same position. The wood in the latter condition appeared more natural in terms of wall thickness and vessel shape; however, the thickness of the wall reduced in the starting position of Stage 2. It may have been caused by the shortage of material for cell production under a high temperature but a short day length

Characterization of Poplar Overexpressing Xylanase

We expressed Hordeum vulgare (barley) xylanase constitutively in Populus tremula x alba (poplar). The expression of xylanase reduced not only the amount of hemicellulose but also the amount of lignin in the secondary xylem. Stem and leaf growth rates were accelerated in transgenic plants. The stems also developed increased flexibility, especially in their younger parts, specifically, the regions above the 10th internode from the top. The secondary walls in the xylem would be slower to mature in xylanase-expressing poplar than in the wild type

Wood Characteristic of Superior Sengon Collection and Prospect of Wood Properties Improvement through Genetic Engineering

Many tree breeding programs ranging from conventional to molecular genetics approach were applied to produce clone or tree genetic industrially desirable wood. This study was aimed to evaluate the wood properties of selected sengon (Paraserianthes falcataria) tree which has high score of  growth parameter and stem form and to evaluate stem properties of transgenic sengon and mangium (Acacia mangium) overexpressing wall hydrolases. Physical and chemical wood properties including basic density, shrinkage and thickness swelling, estimated stand volume, cellulose, lignin and water content were examined for two selected plus tree sengon namely PI and PII, which were grown at Germ Plasm Collection Garden of Research Centre for Biotechnology - LIPI. Both of two sengon tree has high value of  estimated stand volume and basic density (0.43 and 0.49 g/cm3). The PII tree has lower lignin and water content than P I. Cellulase overexpression in sengon and xyloglucanase overexpression in mangium could alter stem cell walls composition. Transgenics mangium stem have higher cellulose content (37.70~53.64%) and lower hemicelluloses content (30~40%) than the wild type.

Intake of Radionuclides in the Trees of Fukushima Forests 1. Field Study

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 the atmosphere and ocean. The radionuclides were deposited onto trees and local residences in aerosol or gaseous forms that were partly absorbed by rain or melting snow. Here, we show that the radionuclides attached to the surfaces of trees, in which some radiocesium was incorporated into the xylem through ray cells and through symplastic pathways. The level of incorporated radiocesium varied based on tree species and age because of the ability of radiocesium to attach to the surface of the outer bark. After four years, the radiocesium level in the forest has been decreasing as it is washed out with rainwater into the sea and as it decays over time due to its half-life, but it can also be continuously recycled through leaf tissue, litter, mulch, and soil. As a result, the level of radiocesium was relatively increased in the heartwood and roots of trees at four years after the event. In private forest fields, most trees were left as afforested trees without being used for timber, although some trees were cut down. We discuss an interdisciplinary field study on the immediate effects of high radiation levels upon afforested trees in private forest fields