To clarify the distribution of radioactive contamination in bed logs, which can transfer to shiitake (Lentinula edodes) fruiting bodies, the concentration of radioactive cesium (Cs) in the trunks of konara oak (Quercus serrata) trees was measured in 10-year-old stands emerging after the Fukushima nuclear accident. While the ratio of Cs concentration (per kg) in bark and stem wood was 1.9 : 1, the overall quantity in bark was 26% of total Cs, due to the relative contributions of bark and wood to trunk weight. This result differed significantly from the distribution of radioactive contamination in standing trees directly affected by the fallout. Disc samples taken from trees at a height of 1 to 3 m revealed that the concentration of radioactive Cs in both the bark and wood tended to be higher at 1 m. On the other hand, in determining correlations in Cs between the trunk (disc) and branch, bark or wood, the highest correlation was found between trunk and wood (R2 = 0.875). These results indicated that an evaluation method using the wood of logs below 1 m of standing trees is effective as a simple inspection method for stands of trees that emerged after the nuclear accident, which are to be used for bed log cultivation of shiitake mushrooms.

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Recently, there has been growing interest in γ-aminobutyric acid (GABA) as a functional component of foods. In the general metabolic pathway, GABA is produced from decarboxylation of glutamic acid by glutamic acid decarboxylase (GAD), which is a pyridoxal 5’-phosphate (PLP)-dependent enzyme. GAD has been reported in various organisms. However, there are few reports of the purification and characterization of the enzyme in relation to GABA formation in Basidiomycetes, including edible mushrooms, even though a number of mushrooms contain GABA in the fruiting body. In this study, we described the purification and characterization of an enzyme related to GABA synthesis from Lentinula edodes. The enzyme was purified to 9.28-fold with a yield of 7.14% by 4 steps, and showed a single band on SDS-PAGE. The purified enzyme from L. edodes showed a wide range of substrate specificity, reacting not only with L-glutamic acid but also L-aspartic acid, aminoadipic acid, ibotenic acid and norvaline; whereas, it is well-known that GAD reacts only with L-glutamic acid. A homology search of the amino acid database using ForestGEN indicated that the internal amino acid sequence of the enzyme was identical to phosphatidylserine decarboxylase (PSD) of L. edodes.

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For transmission electron microscopic (TEM) observation of biological specimens, ultrathin sections are cut from resin-embedded specimens. No data have been reported on the effect of adding an accelerator to the resin mixture on TEM images of mushroom fruiting bodies. The purpose of this study was to evaluate the effect of adding an accelerator to the resin mixture during the resin-infiltration process in the fruiting bodies of Pleurotus ostreatus. When a resin mixture containing the accelerator was used, the plasma membrane and intracellular membrane-bound organelles were clearly detectable. When a resin mixture without an accelerator was used, the contrast was relatively low. In particular, the membrane structure of the mitochondria and most of the nuclear envelope and rough endoplasmic reticulum were not detectable. These results suggest that the use of a resin mixture containing an accelerator is essential during the embedding process for the analysis of intracellular membranes in the fruiting bodies of mushrooms.

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Gymnopilus junonius is widely distributed in Japan and is well known as a hallucinogenic mushroom. A recent study revealed that gymnopilin produced by this mushroom has a biological effect on animal tissues, and its physiological and pharmacological activities have been investigated. In spite of the emerging research interest in this mushroom, the availability of fruiting bodies as a research material has been sporadic owing to the lack of an artificial cultivation method for this mushroom. In this study, we aimed to develop a sustainable cultivation method for G. junonius. Spawned substrates were processed using three treatments: cold stimulation, soaking and casing. Fruiting bodies were not observed on the substrates subjected to cold stimulation or soaking treatment. In comparison, fruiting bodies were consistently produced on the substrate subjected to casing treatment. Fruiting body formation was observed in the medium containing rice bran at 10 － 20% (v/v), but not on those at 0% or over 30%. When the substrate subjected to casing treatment was incubated under light, a high yield of normal fruiting bodies was observed. These results suggest that sustainable fruiting body formation can be achieved in medium containing rice bran at 10%, with casing treatment and incubation under light.

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Production and consumption of jelly fungi, such as Auricularia auricula-judae and Auricularia polytricha, have increased over the past decade. Both of these mushroom species are customarily classified as "kikurage" in Japan. Of those distributed in Japan, 90% are imported from China. This study focuses on the elemental composition of Auricularia species commercially available in Japan (A. polytricha from Japan and China, and A. auricula-judae from China), attempts to identify their elemental characteristics, and investigates the risk assessment of domestic mushrooms. For 20 elements, the content differed significantly depending on mushroom species and geographic origin. Levels for 19 of the 24 elements studied were the highest in A. auricula-judae from China. Major elements (K, Mg, P, and Ca) were higher in A. polytricha from Japan, and elements such as Fe, Mn, Cr, Al, and Pb were higher in A. polytricha from China. Multiple regression analysis indicated that the content of many elements was more influenced by species than geographic origin.

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