桑科植物葉部鈣結晶與培養液中不同鈣離子濃度對小葉桑葉部鈣結晶形成的影響

Abstract

本論文主要是以桑科(Moraceae)植物為材料，觀察各屬植物內鈣結晶體的種類、形態及分佈，並比較屬間之異同。另以小葉桑(Morus australis Poir)為實驗材料，觀察其葉片中碳酸鈣與草酸鈣晶體發育過程中的變化，並探討不同鈣離子濃度水耕培養液對葉部鈣結晶體形成的影響。 桑科植物葉部鈣結晶體觀察於觀察的桑科八屬九種植物葉片中，草酸鈣晶體主要為晶簇形及多面體形，晶簇形分佈於葉肉組織和維管束組織的結晶細胞中，而多面體形晶體僅局限於維管束組織的結晶細胞中；碳酸鈣則形成鐘乳體結晶，位於表皮的石胞內。各屬植物間鐘乳體及石胞形態均不相同，而石胞形態和葉部表皮層數有關：具多層表皮者，石胞為乳頭狀；若為單層表皮，則石胞為毛茸狀。依草酸鈣及碳酸鈣結晶的有無，可將此九種植物區分為三種類型：(a)具草酸鈣及碳酸鈣結晶，包括構樹、島榕、印度橡膠樹、盤龍木及小葉桑。(b)僅具草酸鈣結晶，包括麵包樹、台灣柘樹。(c)僅具碳酸鈣結晶，包括細齒水蛇麻、葎草。 鈣離子對小葉桑葉部鈣結晶體形成的影響 於1/8Ca組｛[Ca2＋]＝0.094mM},1Ca組{?Ca2+]=0.75mM},5Ca組{[Ca2＋]＝3.75mM｝實驗中，葉部結晶細胞及石胞的發育過程，並未隨著鈣離子濃度不同而有所差異，但對葉部鈣結晶體的形成則有明顯影響。 小葉桑之鐘乳體位於葉部上、下表皮之毛茸狀石胞中，由排列成環狀結構及輻射狀條紋之絲狀物組成，其內含有碳酸鈣晶體、不溶性多醣類、蛋白質及胼胝質。草酸鈣晶體位於結晶細胞的液胞中，晶體外為晶鞘包裹，晶鞘含有不溶性多醣類。草酸鈣結晶細胞分佈於葉部之表皮組織、葉肉組織及葉脈中，而分佈於表皮組織及葉肉組織之結晶細胞，均維持原組織之細胞形態與功能。葉脈之結晶細胞則位於木質部和韌皮部之間、維管束鞘及維管束鞘延伸區中，這些結晶細胞之形態較短且寬。葉脈之結晶細胞的細胞核明顯且常被液胞擠壓而位於細胞邊緣，細胞質中粒線體及核醣體數量豐富，色素體及微體亦存在。當含晶體之液胞的液胞膜和細胞膜接觸癒合後，細胞壁開始於晶體表面形成，並逐漸包裹晶體。 當葉片發育至成熟階段時，各實驗組間石胞的密度並無明顯的差異，但對於鐘乳體的形成卻有明顯的影響。於l/8Ca組中石胞僅形成基柄，1Ca組中鐘乳體形狀和野外生長植株葉部的鐘乳體類似，具明顯基柄及體部，而於5Ca組中，大部分石胞則幾乎為鐘乳體所充滿；石胞體積由大而小分別為5Ca組、1Ca組、l/8Ca組。而對草酸鈣晶體形成的影響方面，於1/8Ca組中，僅於葉肉組織及上、下表皮細胞中有細小的草酸鈣晶體，而於1Ca和5Ca組中，除了在上、下表皮與葉肉組織細胞中有細小的草酸鈣晶體外，還有晶簇狀及多面體形晶體於維管束組織中形成。但在5Ca組中，其晶體密度較1Ca組為大。 於植株移植試驗中，由5Ca組移植至l/8Ca組時，植株移植前已達成熟階段的葉片，其葉表毛茸狀石胞內之鐘乳體經移植後並沒有明顯變化，其由碳酸鈣晶體堆積形成的體部並未消失；葉脈中的草酸鈣晶體其體積變小且數目減少。移植後才形成的葉片，達成熟期時其鈣結晶體則和未經轉移試驗之l/8Ca組相似。由1/8Ca組移植至5Ca組時，在植株轉移前已達成熟階段的葉片，於轉移之後無體部形成或僅有細小體部形成；而草酸鈣晶體於轉移後，在葉脈中僅有少量草酸鈣晶體形成，表皮細胞內的細針狀結晶並無很大的變化；而移植後才形成的葉片，於達成熟期時和未經移植之5Ca組植株相似。

The type, morphology and distribution of calcium crystals and trichomes were investigated in the mature leaves of nine species (eight genera) of Moraceae. According to the composition of calcium crystals, the nine species were classified into three groups: (a) both with calcium oxalate and calcium carbonate crystals: Broussonetia papyrifera, Ficus elastica, Ficus virgata, Malaisia scandens and Morus australis (b) only with calcium oxalate crystals: Artocarpus altilis and Cudrania cochinchinensis (c) only with calcium carbonate crystals: Fatoua pilosa and Humulus scandens. All cystoliths consisting of calcium carbonate were located in the epidermal lithocysts. The morphology and the distribution of cystolith and lithocyst are different among genera. The types of lithocystes are related to the layers of epidermis, i.e. trichome-like lithocyst in uniseriate epidermis; papillate lithocyst in multiseriate epidermis. Calcium oxalate crystals were mainly found in the forms of druse or prism. Druses were located in the crystal cells of the mesophyll or the vascular bundle, but prismatic crystals were only found in the cells around the vascular bundles. The cystolith of Morus australis was composed of a stalk and body. In the body there were abundant radial arranged fibrills, which constructed the stratified layers. The cytochemical test showed that the frame of the body was made by polysaccharide, protein and callose, and the calcium carbonate crystal accumulated within. Calcium oxalate crystal cells were found in the epidermis, mesophyll and the cells in or around the veins, such as vascular bundle sheath and bundle sheath extension cells. The shape of crystal cells were mostly wide and short. The oxalate crystals, surrounded by the crystal sheath, was formed in the vacuoles. The mature oxalate crystal cells contained nuclei, mitochondria, plastids and microbodies. As the portions of tonoplast fused with the plasma membrane from where the cell wall formed around the crystal tips. The formation of calcium crystals in the leaves of Morus australis at different levels of calcium supply was also studied. The results showed that the density of lithocysts was not affected by the different concentrations of calcium supply, but the volume of lithocyst ascended from 1/8Ca group to 5Ca group. According to the calcium concentration increments the size of the cystoliths also increased. In 1/8Ca group, only the stalk of the cystolith was formed in the lithocyst. In 1Ca group, the cystolith had both the stalk and body structure as that of the wild plant. While in 5Ca group, the lithocyst was almost filled with the cystolith. Besides, the formation of the calcium ‘oxalate crystals was influenced by the different calcium supply as well. No oxalate crystal was found