榕樹皮孔發育過程的變化

Abstract

本論文以榕樹（Ficus microcarpa L. F.）?材料，觀察其枝條與氣根上成熟皮孔的形態與解剖，也觀察枝條泡水後皮孔的變化。此外，並探討幼嫩枝條上皮孔發育過程中，其顯微構造與細胞化學的變化。 榕樹枝條與氣根上成熟的皮孔，呈透鏡形小點分散地突起於表皮，?縱向開裂，而其組成細胞由內而外?栓皮層、皮孔木栓形成層及成層交替排列的封閉層與充塞細胞，皮孔內的單寧細胞常沿徑線方向成列排列。 枝條泡水部份的節間之皮孔有腫大的現象，其皮孔木栓形成層向外分裂細胞的能力增加，但新形成的細胞皆?排列疏鬆的長桿狀薄壁細胞。 枝條上的皮孔均起源於氣孔下方的組織，茲將其發育過程區分?：皮孔木栓形成層的起源、封閉層與充塞細胞的形成及成熟皮孔等三個階段。 1．皮孔木栓形成層的起源 由氣孔下方排列疏鬆的薄壁細胞，即前充塞細胞群進行各方向的細胞分裂，但在此群細胞下緣之細胞則皆行平周分裂，而這些細胞分裂面幾乎連成一弧形，即成?皮孔木栓形成層。前充塞細胞及初形成的皮孔木栓形成層細胞細胞質內含細胞核、葉綠體、高爾基體、粒線體、內質網、核糖體，以及大型液胞等胞器。各細胞間以細胞質連絡絲相通。 2．封閉層與充塞細胞的形成 皮孔木栓形成層和一般周皮的木栓形成層相連，但向內凹陷。由其向內分裂一至二層栓皮屑，栓皮細胞不進行次生細胞壁的加厚；向外則首先形成排列緊密且具木栓化細胞壁的封閉層，接著連續分裂一至四層排列疏鬆，且具薄壁的充塞細胞。隨著細胞層數的增加與細胞生長而產生的壓力，使得表皮破裂，位於其下的前充塞細胞隨之掉落，封閉層便取代表皮的地位。此階段內各細胞之葉綠體逐漸轉變成色素體，其餘胞器種類與前階段之前充塞細胞相似。成熟的前充塞細胞及封閉層細胞之細胞壁有木栓化的層狀構造。皮孔木栓形成層細胞?單寧細胞者，由其分裂而來的所有細胞皆具分泌物質的能力，於是皮孔內單寧細胞均沿著徑線方向成列排列。 3．成熟皮孔 皮孔木栓形成層向外交替形成交替產生封閉層與充塞細胞群，使得位於外層的封閉層因其推擠而逐層破裂、脫落，而位於其下充塞細胞也隨之逐群脫落，在一成熟皮孔中大約保持兩層完整的封閉層，其外常有未完全脫離的充塞細胞與封閉層片段。成熟的封閉層細胞在外切線面上木栓化加厚的細胞壁，皆脫離初生細胞壁而向內凹陷，而其液胞內可觀察到絲狀片段物質。 榕樹皮孔組織化學測定結果顯示：木栓質堆積在成熟之前充塞細胞與封閉層細胞之細胞壁上。就第二階段皮孔之酸性磷酸?次細胞定位，發現前充塞細胞、充塞細胞、皮孔木栓形成層及栓皮層細胞內皆有酸性磷酸?的分佈，而封閉層細胞則只有在細胞質連絡絲上檢測出酸性磷酸?。第三階段之多醣類及脂質測定顯示乳汁細胞內含物含有多醣類與脂質；封閉層細胞細胞壁與細胞質皆有脂質的分佈，其細胞壁亦有多醣類的成份。

The morphology and anatomy of lenticels on the branches and aerial roots of Ficus microcarpa L. f. were examined. The changes of lenticels after immersion and the ultrastructure and histochemistry for the developmental stages of lenticels on branches were also studied in the present work. The mature lenticels on the aerial roots and branches of Ficus microcarpa L. f. are mainly lens-shaped. Besides, they are convex towards both the exterior and interior. The lenticels are centrifugally composed of phelloderm, lenticel phellogen, and several strata of complementary cell layers alternated with single closing layers. In the lenticel, several rows of radial arranged tannin cells were observed. Lenticel hypertrophy arised in the immersed internodes. It was characterized by the large and loosely interconnected thin-walled cells. The development of the lenticel could be devided into following three stages: 1. the initiation and formation of lenticel phellogen The division of the precomplementary cells beneath the stoma progressed in the cortex inwards and the orientation of the divisions became more and more periclinal until the lenticel phellogen is formed. In the precomplementary cells and the cells of lenticel phellogen, the single nucleus, large vacuoles, chloroplasts, dictyosomes, mitochondria, endoplasmic reticulums and ribosomes were investigated. There were many plasmodesmata which connected adjacent cells. 2. the differentiation of the complementary cell and closing layer The lenticel phellogen was found to be continuous with that of the periderm, but it was usually bended inward. Centrifugally, the phellogen of lenticel produced one layer of compact suberized closing layer and then one to four layers of unsuberized complementary cells. The increase in number of these cells caused the rapture of the epidermis so that the precomplementary cells are pushed out. The outermost closing layer replaces the epidermis to be the protect layer. The precomplementary cells were also suberized and the chloroplasts in them were transfered to be the plastids. But all the other organelles in the precomplementary cells were similar to that of previous stage. 3. mature lenticel The phellogen of lenticel produced closing layers and complementary cells alternately. Hence, the cells of the exposed layer died and withered away. Generally, in a mature lenticel only two compact strata of closing layers were observed. The suberized outer tangential walls in the mature cells of closing layer were found to be separated from their primary walls and thus the cells were concave in shape. In the central vacuoles of mature cells of the closing layer, fragements were observed. With the histochemical tests the followings were investigated. The suberin was found to be located in the cell wall of mature precomplementary cells and the cells of closing layers. Lipid was detected both in the cytoplasm and cell wall of the cells of closing layer, but polysaccharide was found only in the thick walls of closing layers. The subcellular localization of acid phosphotase in the lenticel showed that acid phosphotase were mainly distributed in the cell wall, vacuoles against tonoplast, and dispersedly in plastid and cytoplasm of precomplementary cells, complementary cells, lenticel phellogen as well as phelloderm. However, in the closing layer, acid phosphotase was detected only in the plasmodesmata.