フリージアの球茎発育に関する組織学的研究

Abstract

The processes of formation and maturation of freesia corms were studied by histological and histochemical procedures.The experiments consisted of two parts. In the first experiment, cormlets of cv. ‘Rynveld′s Golden Yellow’, after forced to sprout, were planted in the greenhouse on September 18, and were harvested at intervals of one or two weeks until May 21 of the following year. At each sampling date, new corms were fixed and examined microscopically.In the other experiment, the corms grown in the greenhouse were harvested at about monthly intervals from March to June. The quantitative changes of RNA contents in the cells of the apical meristem of new corm, which were involved in maturation, were investigated histochemically. For the corms harvested in June, the effect of warm storage on the RNA contents was also examined by the same procedures.The results obtained were summerized as follows:1. The mother cormlet, average weight of which was about 1.0g, had five alternately arranged primordia of leaves in its main bud. The outer four of these five primordia developed to sheath leaves, and the innermost one developed into the first foliage leaf.2. After growth for eight to nine weeks, remarkable swelling of internodes between the second and the fourth foliage leaf was observed. The swelling of internodes resulted from the rapid cell division in the parenchyma of cortex. This was the start of the formation of new corm. At the same time, the differentiation of inflorescence was observed on the shoot apex.3. The development in diameter of new corm mostly depended on thickening growth of the cortex. The thickening growth of the cortex might be divided into three stages.At the initial stage, 12 weeks from forcing to sprout, the thickening growth of the cortex depended on cell multiplication. At the second stage, the succeeding five weeks of growth, cell division and cell enlargement were observed simultaneously. At the third stage of the last 20 weeks of growth, cell division had nearly ceased and the thickening growth of the cortex was caused by cell enlargement.4. In ten weeks after planting, growth of the daughter plant had been released from dependence upon the reserved substances of mother cormlet. At the same time, storage starch grains appeared in the parenchyma cells of new corm.5. At the early stage of growth, thickening was exclusively caused by increase in the number of cells due to the apical meristem activity of new corm. In the successive thickening growth of new corm, however, the actively dividing cells which diffused in the parenchyma of cortex played an important role. Therefore, it may be concluded that the pattern of the thickening growth of freesia corm is “diffuse thickening growth”, which is one of the pattern of thickening growth observed in stems of monocotyledons.6. A large amount of RNA was observed in the apical meristem of new corm harvested in March, demonstrated by the azure B method. The measurement by microspectrophotometry, however, showed that the RNA contents of cell in the apical meristem decreased progressively thereafter. Almost all the RNA in the meristem disappeared when new corms were placed in warm storage.When the new corms were moved to optimum conditions for sprouting, the RNA content in the meristem increased rapidly. In this case, within a certain range, the longer the period of warm storage, the more rapid the increase of RNA content was.