仮道管切開法による細胞壁構造の研究

Abstract

針葉樹仮道管を切開法によって平面に展開し, 半径壁と接線壁を同一平面上で観察することを試みた。切開操作はミクロマニピュレーターで行ない, 切開仮道管は電顕的あるいは光顕的に観察した。この方法で完成した春材仮道管ばかりでなく, 二次壁形成中の春材仮道管も切開することができた。春材仮道管の二次壁中層 (S_2) のミクロフィブリル傾角を, この方法を適用して一仮道管内の半径壁と接線壁で比較した。その結果, 仮道管中央部の膜孔のない半径壁とそれに隣接する接線壁との間には傾角の顕著な差は認められなかった。一方, 半径壁に膜孔の存在する場合, 特に先端寄りの部分では, その上下近辺で傾角が大きくなり, 接線壁との差は主消光位で比較すると15 - 20°に達した。

The microdissection technique for a single tracheid, originated by DUNNING (1968, 1969), was further developed in order to observe simultaneously both radial and tangential walls at an even level, along the length of an individual tracheid. Mature or partially differentiated earlywood tracheids were isolated by chemical treatment with Jeffrey's solution and then freeze-dried. They were pressed onto the surface of dried rubber cement (Neoprene W) (Figure, a). The upper side of the tracheid wall was slit open with a knife, which was made in the same manner as described by DUNNING (1969). The slit tracheid was then spread out flat with the knife edge and a glass needle, exposing the lumen surface (Figure, b and c). The knife and glass needle were controlled with a micromanipulator. The flattened tracheids were either mounted, without further treatment, in Canada balsam for optical microscopy (Photos. 1 and 3); were coated with carbon and gold for scanning electron microscopy (Photo. 2); or were replicated with the two-step method (ethylmethacrylate-carbon, Pt-Pd shadowed) for direct observation of microfibril orientation. Through this technique the microfibril orientation in the S2 layer of radial walls and that of tangential walls were compared within an individual earlywood tracheid. From observations of replicas (Photos. 5 and 6), the major extinction position between crossed nicols (Photo. 7), and the cavities produced by soft-rot fungi (Photo. 8), it was found that in the central region of the tracheid there were few differences in the microfibril angle between the unpitted radial wall and the neibouring tangential wall. On the other hand the pitted radial wall, particularly towards the cell tips, showed a greater angle than the adjacent tangential wall. The difference was estimated to be 15-20 degrees, based on the major extinction position (Photo. 7).