コナラ属木材の道管放射組織間の壁孔対

Abstract

日本産コナラ属樹種 (アベマキ, クヌギ, ミズナラ, コナラ, カシワ, ウバメガシ, アカガシ, シラカシ) の道管放射組織間の壁孔対 (R-V pit) を走査電子顕徴鏡で観察し, 次にコナラのR-V pitについて, 壁孔膜の隆起と孔口周辺の壁の肥厚経過を4月から9月まで時期別に調べた。1. 春材部道管におけるR-V pitの形態を走査電子顕徴鏡で観察すると, (a) アベマキとクヌギは長楕円形, 格子状, (b) ミズナラ・コナラならびにカシワは小円形, 対列または交互状, (c) ウバメガシは長楕円形, 格子状, (d) アカガシとシラカシは長楕円形, 顕著な格子状を示した。2. 壁孔対については, 放射柔細胞の孔口の方が道管側の孔口より狭いもの (a, b) と等しいもの (c, d) にわかれた。前者では, 道管側R-V pitの孔口周辺に隆起があり, 道管内腔からみるとドーナツ状の形態を示した。3. コナラの生立木より試料を採取し, 固定・脱水 (アルコールシリーズ) 後, 臨界点乾燥して観察すると, ドーナツ状の形態は見られず, 道管側へ壁孔膜がドーム状に隆起 (protrusion) しているだけであった。よって樹木内で道管側に隆起していた壁孔膜が乾燥などにより落ち込むと考えられる。4. 放射柔細胞の内腔側には, 未木化 (低電子密度) の層がある。この層は夏以降, 特にR-V pit周辺でより厚くなり, 木化し, 壁孔膜を道管側に押し出す。壁孔膜の隆起は5月頃より認められる。

Ray-vessel pit pairs of the Japanese Quercus wood were observed by a scanning electron microscope. After that, the protrusion of the pit membranes and cell wall thickening around the pit pairs were investigated using samples taken from living trees of the Q. serrata during the time period from April to September. 1. In early wood vessels the shape and arrangement of R-V pits when viewed from vessel lumen were elongated elliptic, palisade-like arranged in (a) Q. variabilis and Q. acutissima, small circular, opposite to alternate in (b) Q. serrata and Q. monglica var. grosseserata, variable but mostly elongated elliptic, palisade-like arranged in (c) Q. phillyraeoides, and elongated, distinctly palisade-like arranged in (d) Q. acuta and Q. myrsinaefolia. 2. Ray-vessel pit pairs of wood (a) and (b) had smaller pit apertures on the ray cell wall than on the vessel wall, but those of wood (c) and (d) had nearly the same aperture width on both walls. In the former wood a circular protrusion of the pit membrane occurred around the pit aperture of the vessel wall, havidg a doughnut-like appearance in the vessel side view (Photo 2). 3. When wood samples taken from living trees of Q. serrata were investigated after fixation, alcohol series dehydration and crictical point drying, R-V pit membranes protruding toward vessel lumen appeared as circular domes. Their doughnut-like protrusions were considered to be formed due to a sinking back of the dome of the protruded membrane during the seasoning of the wood. 4. A low electron dense layer (or protective layer) was observed on the lumen surface of the ray parenchyma cell. After summer, the layer was thickened and lignified especially where the wall tauched the adjacent vessel wall. Around the R-V pit pair the thickened and lignified layer decreased the pit aperture width of the ray cell side and pushed the pit membrance into the vessel lumen. After May, protrusion of the membrane was observed.