Early response of ray parenchyma cells following wounding in sugi (Cryptomeria japonica D. Don) wood : Seasonal changes of discoloration and cytological structure

Abstract

傷害に対する木部柔細胞の初期の反応を, 主として細胞学的な観点から検討した。このため実験的に機械的傷害を与え, 傷害を与えた時点で木部を構成していた組織の変化を, 各季節において, 時間的経過を追って観察した。なお, 機械的傷害として1組の剥皮を行い, 一方はそのまま放置 (open) し, 他方は傷害後ただちに表面をエポキシ樹脂系接着剤で被覆 (sealed) した。得られた結果は以下のとおりである。(1) 傷害後木部は一般に変色を示した。変色の広がりは季節により異なった。すなわち春・夏には変色は広範囲に広がり, 秋にはやや狭く, 冬には最小値を示した。(2) 放射柔細胞内容物の変化は, 春・夏と秋・冬で異なった。すなわち前者では, 核の変形, 細胞質基質の変色, 貯蔵物質の減少の順に生じたが, 後者では細胞質基質の変色の後に核の変形がおこった。(3) openとsealedの両者において, 材の変色や放射柔細胞内容物の変化が見られた。しかしopenの方が一般に変化範囲が広く, また変色は濃色を示した。(4) 変色と菌類との関係を検討したところ, 材の変色にとって, 菌類の存在は必須のものではないと判断された。(5) 以上の結果から, 樹幹は機械的傷害に伴い, 必ず変色することが明らかになった。また傷害に伴う組織の生理的条件の変化が, 変色に必須であると判断された。

Early response of wood parenchyma cells present at the time of wounding was investigated mainly from the cytological point of view. A couple of superficial mechanical wounds which were made by removing bark was inflicted on the trunk in every season. One of the wounds was kept in open condition to the air and the surface of the other was sealed by an adhesive of epoxy resin immediately after wounding. From the observation of the changes of wood after wounding, following results were obtained; (1) Wood generally showed discoloration following wounding. The extent of discoloration showed seasonal fluctuation. In spring and summer in which the cambium is in the active condition the discoloration extended widely. The extent of discoloration decreased in autumn and showed minimum in winter. (2) Cytological changes of ray parenchyma cell contents were different between spring to summer and autumn to winter. From spring to summer, the first symptom of cytological changes was deformation of nucleus which was followed by the discoloration of cytoplasmic matrix and decrease of reserve substances. In autumn and winter, on the other hand, the discoloration of cytoplasmic matrix was followed by the deformation of nucleus. (3) Comparing the open wounds with the sealed ones, both showed the discoloration of wood and cytological changes of ray parenchyma cell contents. The open wounds showed, however, wider extent of cytological changes and also showed darker discoloration than in sealed condition. (4) From the investigation of the relationship between discoloration and fungi it was considered that the existence of fungi was not the indispensable condition for the discoloration of wood. (5) From the results mentioned above, it was revealed that the xylem necessarily showed discoloration following wounding. One of the causes of discoloration was supposed to be the changes of physiological condition of the tissues and cells following wounding.