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Title: 一仮道管内の長さ方向における細胞壁厚さの変異
Other Titles: The Variation in the Cell Wall Thickness along the Length of a Conifer Tracheid
Authors: 奥村, 正悟  KAKEN_name
原田, 浩  KAKEN_name
佐伯, 浩  KAKEN_name
Author's alias: Okumura, Shogo
Harada, Hiroshi
Saiki, Hiroshi
Issue Date: 14-Dec-1974
Publisher: 京都大学農学部附属演習林
Journal title: 京都大学農学部演習林報告
Volume: 46
Start page: 162
End page: 169
Abstract: アカマツの一仮道管内の長さ方向における二次壁中層 (S_2) の厚さ変化を, 春材と夏材について, 連続木口切片でSEMを用い検討した。夏材仮道管では, 接線壁のS_2層はその全長にわたってほぼ一様であったが, 半径壁では中央部で最も厚く先端に向って顕著に減少し, それは接線方向直径の減少とかなりの直線的相関を有していた。また仮道管の中央部では半径壁でのS_2層が接線壁のそれよりも厚いが, 先端部ではその関係は逆になっている。春材仮道管ではS_2層の厚さはほぼ一様と考えられ特別な変化傾向は見出し得ななかったが, 全長にわたって常に接線壁での厚さが半径壁よりも大きかった。S_2層の断面積は夏材仮道管の場合には長さ方向のかなりの範囲にわたって変化するが, 春材の場合には先端の極近くで減少するのみであった。春・夏材とも放射組織との交差域で断面積が減少することは見られなかった。
The thickness variation of the S2 layer along the length of a mature tracheid was studied by serial transverse sectioning to examine the Wardrop's progressive longitudinal deposition theory for secondary wall layers. The 1-2 μ thick sections were obtained from the epoxyembedded materials (Pinus densiflora SIEB. et ZUCC.) using a glass knife; were mounted on a small piece of glass slide (ca 8×8mm); and then were dried. After removing the embedding medium with KOH saturated ethanol solution, the sections were coated with carbon and gold and examined in a JSM-U3 scanning electron microscope. Cells were arbitrarily marked to be followed from section to section. In a latewood tracheid, the thickness of the S2 layer was relatively uniform along the tracheid length in the tangential wall, whereas in the radial wall it conspicuously decreased from the mid-region of the tracheid towards its tip (Photo. 2; Fig. 1). The S2 layer was much thicker in the radial wall at the mid-region of a tracheid than in the tangential one, but the relation reversed near the tips (Figs. 1 and 3). The reduction in thickness towards the cell tips appeared to be related to the tangential diameter of cells (Fig. 1). The thickness, in fact, showed a linear relationship to the tangential diameter (Fig. 6). In an earlywood tracheid, the S2 layer did not distinctly reduce the thickness towards cell tips, but it might show the rather even thickness through the tracheid length, especially in the radial wall (Photo. 3; Fig. 4). As contrasted with a latewood tracheid, the S2 layer thickness in an earlywood tracheid was greater in the tangential wall through the whole length than in the radial one (Fig. 4). Incidentally, the area of the S2 layer in the transverse sections also decreased gradually from the mid-region of the latewood tracheid towards its tip (Fig. 2), and the decrease was constantly related to the tangential diameter (Fig. 7), while in an earlywood tracheid it showed a slight decrease only in the close vicinity of the tips (Fig. 5). The reduction of the S2-layer area was seldom recognized in the region where the tracheid crosses the ray, though a distinct increase was sometimes observed in an earlywood tracheid (Figs. 2 and 5). Because of the considerable variation in wall thickness, not only along the tracheid length, but also between the radial and the tangential wall, the mechanism and the process for the secondary wall deposition need further examination.
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