針葉樹二次木部放射柔組織のエイジングに伴う細胞生存率の変化

Abstract

針葉樹について, 辺材部の放射柔細胞が形成層からの加齢すなわちエイジングの過程で示す変化を, 細胞生存率という観点から調べた。得られた結果は以下の通りである。1. 放射柔細胞が壊死し始める位置からは, 3つの型に分類された。すなわち, I型 : 辺材部のすべての放射柔細胞が生存しているタイプ (アカマツ・ゴヨウマツ・イチイ・アスナロ・ネズミサシ・コノテガシワ)。II型 : 辺材内層部において放射柔細胞が壊死し始めるタイプ (スギ・ヒノキ・カヤ・トガサワラ・ツガ)。III型 : 辺材外層部において放射柔細胞が壊死し始めるタイプ (モミ・カラマツ・トドマツ・ヨーロッパトウヒ) である。2. 辺材中で壊死する放射柔細胞中には, 脂質 (スギ・ヒノキ等), 結晶 (モミ・ヨーロッパトウヒ), タンニン (ツガ・カラマツ) 等が含まれていたが, すべての樹種において, でんぷんは全く存在しなかった。3. 辺・心材境界またはその近くで, 細胞生存率が急激に低下する場合は, 生理学的に見て, 辺・心材の境界が明確な樹種と推定される。

In order to obtain some fundamental information on the role of wood parenchyma, the rate of survival of ray parenchyma cells was investigated. Specimen blocks were taken from 20 coniferous trees by means of an increment borer. The blocks, which included sapwood and heartwood, were fixed in 3% glutar aldehyde. Series of radial-longitudinal sections were cut to cover the distance from cambium to pith and stained with safranin-light green. Other staining methods were also employed. From the position of the dying of ray parenchyma cells, survival curves showed three types. Type I: All cells survive from cambium to the transition zone between sapwood and heartwood (Akamatsu, Goyômatsu, Ichii, Asunaro, Nezumisashi, Konotegashiwa). Type II: A part of ray parenchyma cells die in the inner sapwood (Sugi, Hinoki, Kaya, Togasawara, Tsuga). In this type the dying of the ray cells starts generally in the upper and lower cell rows of ray parenchyma or in the cell rows adjacent to ray tracheids. Type III: A part of ray parenchyma cells die in the outer sapwood (Momi, Karamatsu, Todomatsu, Yôroppatôhi). From the lightmicroscopy, the inclusions of dead cells were lipid (Sugi, Hinoki etc.), crystals (Momi, Yôroppatôhi) and tannic materials (Tsuga, Karamatsu) and no starch grains were observed in all species investigated. The tree species which showed abrupt decrease of the rate of survival in the inner sapwood or the transition zone between sapwood and heartwood would belong to the group having physiologically distinct boundary between sapwood and heartwood.