クリにおけるチロースの形成と壁構造

Abstract

クリの培養チロースは7-35℃の全ての培養温度で形成されたが, チロース壁はほとんど肥厚しなかった。傷害チロースは壁の伸張後肥厚し, 盲壁孔様構造を形成した。壁の肥厚時には, チロースを形成中の柔細胞内にも新たな壁の肥厚が同時に認められた。壁の木化は肥厚にやや遅れて外側から内側へ進行した。また, クリでは冬期にも傷害チロースが形成された。天然チロースは辺材―心材移行域で年間を通じて形成されるものと思われる。壁の伸張・肥厚・木化過程は傷害チロースと同様であると考えられるが, 天然チロースでは壁の木化後, チロースとそれを形成した柔細胞の内壁全面に再び protective layer 類似の壁層が形成された。時には, さらに盲壁孔様構造より小チロースを形成し, 壁肥厚を行なうことも観察された。

The formation and wall structure of incubated, traumatic, and natural tyloses in Castanea crenata SIEB. et ZUCC. were observed. (1) "Incubated tyloses" were induced in the growth chambers7) maintained at 7, 14, 20, 27, and 35℃. Abundant tyloses developed at each temperature, although they developed slowly in lower temperature (Fig. 1). The incubated tylosis wall was stained with OsO4 in the same density as the innermost protective layer in the parenchyma cell which was forming the tylosis, and it had a thickness of 0.2-0.3 μm. The incubated tylosis wall hardly thickened. (2) "Traumatic tyloses" were induced in two living trees which were bored with a drill. The development of traumatic tyloses in earlywood vessels of the current-year growth ring from August to September was as follows: many tylosis buds were enlarging after 2 days from the boring. After 5 days from the boring tyloses blocked the vessel lumina and their walls were thickening. The wall of parenchyma cells which were forming the tyloses also thickened simultaneously with thickening of the tylosis wall (Fig. 5). Parallel-oriented microtubules were observed near the plasmalemma of tylosis in the thickening stage (Fig. 3), and the wall formed in this stage exhibited highly oriented microfibrillar structure (Fig. 7). Blind pit-like structures of tylosis wall were also formed in the thickening stage (Fig. 4). Judging from the stainability with KMnO4, outer part of the tylosis wall began to be lignified immediately after the wall began to thicken (Fig. 6). The lignification proceeded to inner part of the wall, following after the proceeding of wall thickening (Figs. 4, 5, 7). After 15 days from the boring the tylosis wall had a thickness of about 1 μm, and was wholly well lignified. Traumatic tyloses developed even in winter, although they developed very slowly (Fig. 8). (3) "Natural tyloses", which were formed normally in a living tree (Fig. 9), developed in the transition zone (Fig. 10). A small number of developing tyloses formed mainly from a ray parenchyma cell were found in the vessels adjacent to heartwood zone. Enlarging buds (Fig. 11) and the tyloses in the wall thickening stage were observed all the year round. Natural tyloses, therefore, seem to be formed throughout the year. Wall formation in natural tylosis appears to proceed through the same steps as traumatic tyloses. Well-lignified wall of the natural tylosis had also a thickness of about 1 μm, and its structure was similar to that of a traumatic tylosis. The wall of parenchyma cells which were forming natural tyloses also thickened in the thickening stage of the tylosis wall. This wall was, however, not deposited on the pit membranes of interparenchymatous pit-pairs. After the lignification stage natural tyloses and the parenchyma cell from which the tyloses were formed deposited one more osmiophilic layer again (Fig. 12). This layer was observed on the whole inner surface of their walls, and it was similar to the innermost protective layer found in a parenchyma cell. The tylosis-parenchyma cell complex with the osmiophilic [Figure omitted] Fig. 2 Traumatic tylosis wall in the enlarging stage. The tylosis has a single osmiophilic wall in this stage. a: fixed with glutaraldehyde (GA) and OsO4. b: fixed with GA and KMnO4. Tylosis wall appears to be swollen with KMnO4. Fig. 3 Traumatic tylosis wall in the thickening stage, fixed with GA and OsO4. The inner light wall (electron-transparent) is thickening in this stage. Many microtubules can be observed (arrows). Fig. 4 Blind pit-like structures of traumatic tyloses in the thickening stage, fixed with GA and KMnO4. a: a pit-like structure is formed in this stage. The outer tylosis wall formed in the enlarging stage is densely stained with KMnO4. b: no plasmodesmata are found on the tylosis walls corresponding to the pit membrane, although pit-like structures are forming a pair. Fig. 5 Traumatic tylosis-parenchyma cell complex in the thickening stage, fixed with GA and KMnO4. a: the thickening wall of the complex is less stained and light-colored in this stage. b: enlarged view of the ray-ray pit-pair shown in a. The pit membrane is covered only by a protective layer, and the thickening light wall is not observed on it. Fig. 6 Traumatic tyloses in the early period of thickening stage, fixed with GA and KMnO4. Fig. 7 Oblique section of traumatic tylosis wall in the lignification stage, fixed with GA and KMnO4. The fibrillar pattern (broken lines) indicates a highly oriented microfibrillar structure in the thickened wall. Fig. 8 Radial view of traumatic tyloses developing in the current-year growth ring in winter. a: the tylosis buds after about 3 weeks from the boring. b: the tyloses after one and a half months from the boring. Fig. 9 Radial view of natural tyloses in heartwood. ABBREVIATIONS T: tylosis Tw: tylosis wall P: pit-like structure N: nucleus R: ray parenchyma cell PL: protective layer V: vessel Vw: vessel wall [Figure omitted] [Figure omitted] layer sometimes formed tyloses again (Figs. 13, 14), and it often stored many starch grains (Fig. 15). The whole tylosis-parenchyma cell complex seems to behave as a single parenchyma cell. Fig. 10 Radial view of natural tylosis buds developing in the transition zone. Fig. 11 Enlarging natural tylosis buds with a single osmiophilic wall sampled in January, fixed with GA and OsO4. Fig. 12 Osmiophilic layer (arrow) in a well-lignified natural tylosis, fixed with GA and OsO4. This layer is also observed on the tylosis wall corresponding to the pit membrane as shown in b. Fig. 13 Small natural tylosis with two tylosis buds. Fig. 14 Small natural tylosis (T) with a small tylosis (T′), fixed with GA and OsO4. A pit-like structure (P) may be formed first in the tylosis (T) as illustrated in b. After the osmiophilic layer (arrows in a, and the broken line in b) is deposited, the tylosis (T′) may be formed again. The outer dark wall of the tylosis (T′) is also joined with the osmiophilic layer, and the inner light wall of tyloses (T′and T) and the ray parenchyma cell (R) may be formed simultaneously. Fig. 15 Starch grains stored in the natural tylosis with the osmiophilic layer, fixed with GA and OsO4.