기생피자식물 새삼(Cuscuta japonica Choisy)에서 흡기(吸器)의 구조와 발달

Abstract

The structure and development of the haustorium of a parasitic angiosperm Cuscuta japonica Choisy growing on the host plant lmpatiens balsamina L.. was studied with light and electron microscopy. Three-day-old seedlings of the parasitic plant grew at 30℃ in the dark and for three days in the light. As these Six-day-old seedlings were made in contact with the host plant stem, the upper hasutorium, which lies external to the host organ, was initiated endogenously from cortical cells at the middle layers of the parasite stem at the contact side. The initial cells possessed large nuclei and dense cytoplasm containing a lots of cell organelles such as dictyosomes, mitochondria, rough endoplasmic reticulum, plastids with starch grains and thylakoids, and lipid droplets. As the contact between the parasitic and host plants was kept, haustorial initial cells were developed into a group of meristematic cells. Cytological feature of the meristematic cells was similar to that of the initial cells. Especially the meristematic cells had plastids with developed thylakoids, abundant ribosomes, and several small vacuoles with electron-dense particles. At this time, epidermal cells of the parasite stem at the contact side had dense cytoplasm and conspicuous nuclei and were changed into somewhat elongate form. As the haustorial maturation was progressed, the meristematic cells developed into an upper haustorium, that consisted of three cell types: (ⅰ) at the central region, very enlarged elongate cells (digitate cells) with very dense cytoplasm and large nuclei; (ⅱ) at the proximal to the digitate cells, smaller file cells with conspicuous nuclei, and (ⅲ) at the distal to the digitate cells, compressed cells. The file cells were divided periclinally and anticlinally, and thus they were arranged in several files. The digitate cells contained very large nuclei with a few nucleolei. Their dense cytoplasm including various and abundant organelles: especially the digitate cells contain a few types of plastids that had thylakoids, crystalline inclusion, and starch grain. Ultrastructural evidence was suggested that the digitate cells were metabolically very active. It was thought that the three cell types was formed to invade into the host tissue. On the other hand, Tips of elongate epidermal cells at the side contacted host were branched like toes, in which cytoplasm and nuclei were localized. ln the cytoplasm of the branched tips, vesicles containing electron-dense particles were fused with plasma membranes and the particles were released into walls and then were secreted to spaces outside the folded-walls. It was interpreted as the secreted material might play a important role in cementing the upper haustorium on the surface of host organ.