針葉樹仮道管膜の形成と構造 : 2次膜の交差・移行構造

Abstract

形成過程にある仮道管膜を順次その内表面から追跡していく方法を用いて, アカマツ春材仮道管の2次膜における交差および移行構造について観察を行なった。その結果, 2次膜形成においてはミクロフィブリル配向を一にするミクロラメラ 〔1ミクロフィブリルのならび〕 が, 細胞膜内表面上に順次堆積していくのがみられる。S_1においては細胞軸にほぼ直角の傾角をもつミクロラメラが, ミクロラメラ相互間で多少その傾角を変えながら100枚前後堆積する。この際, 同一傾角をとるミクロラメラの枚数が一定でないため, ミクロフィブリルはあるときは交差して, またあるときは単一の方向に配向しているように観察される。またS_1とS_2, S_2とS_3との間には順次その傾角を変えていく移行構造がみられた。

The method for observing the inner surface of differentiating tracheids was developed in order to study the formation and organization of the secondary wall in coniferous tracheids. It is the purpose of this paper to detect generally the crisscrossed lamellar structure in the S1 and S3, and the "transition" lamellae between the S1 and S2 and between the S2 and S3, both of which have not been resolved in previous studies. The preparation method for replication was the same as that was described in the preceeding paper and the tracheids studied were from springwood of Pinus densiflora S. et Z. In the inner surface of the developing secondary wall, microfibrils were found to be deposited to form the "microlamella" in which the microfibrils lie parallel to each other. They have a constant distance of about 700 ~ 800Å (Plate 1). The progressive development of successive microlamellae was observed in the inner surface of one tracheid forming the S1 layer (Plate 2). This observation confirms the hypothesis of Wardrop and Harada that the secondary wall formation begins near the middle of the fiber and proceeds towards the ends. In the S1 layer if some microlamellae of the same microfibril orientation are deposited, simple helical orientation will be detected (Plate 4, Fig. 1 c), but if newly deposited microlamellae go through a small change in orientation, the crisscrossed structure will be observed (Plate 5, Fig. 1 d). Though serveal microlamellae are deposited in the same direction as the new one, simple helical orientation will appear again (Fig. 1 f). So the crissrossed appearance is observed, not only because successive lamellae have alternating right- and left-hand spirals, but also because the newly deposited microlamellae have the small changes in fibril orientation from the underlying lamellae. The number of microlamellae of the S1 is supposed to be about 100 as determined by observing the scale-like texture of the pit border in cross sectional view (Fig. 2). The S3 was shown to be composed of microlamellae with varying amounts of shift in orientation. And also the change of orientation appeared to decrease as the formation of the S3 terminates (Plates 6 and 7). But the arrangement of microfibrils in a microlamella of the S3 is not as good as that in the S1. The transition lamellae were observed where the microfibrillar orientation exhibits a stepwise transition into the orientation of the next layer bteween the S1 and S2 and between the S2 and S3 (Plates 8, 9 and 10). It is observed that the transition from S1 to S2 is gradual while from S2 to S3 is abrupt.