Motive Force of the Cell Mass of the Cellular Slime Mould Dictyostelium Discoideum : (I) Migrating pseudoplasmodium under dark condition (II) Migrating pseudoplasmodium under illuminated condition (III) Culminating fruiting body

タイトル: Motive Force of the Cell Mass of the Cellular Slime Mould Dictyostelium Discoideum : (I) Migrating pseudoplasmodium under dark condition (II) Migrating pseudoplasmodium under illuminated condition (III) Culminating fruiting body 著者: Kitami, Masanobu 抄録: Here some preliminary results about the motive force of the cell mass of D. discoideum are presented, which seem to be very significant in order to establish a model on following singular collective motions played by cells. The cells of D. discoideum show unificative collective motions, which are characterized as aggregation, migration, and culmination. These collective motions are likely to be very important and essential for their morphogenetic movements ; however, very little is known about the mechanism of such collective motions. Many investigations and detailed explanations on particular life cycle of D. discoideum and some experimental observations on the subjects above mentioned have been described in some books (Bonner, 1967 ; Loomis 1975 ; Cappuccinelli & Ashworth, 1977 ; Maeda & Maeda, 1978 ; Yamada, 1980). In this paper, attention will be paied mainly to migration and culmination. The present measurements were performed by an original method utilizing the centrifugal force. The maximum value of the motive force of a migrating pseudoplasmodium in the dark was estimated as 0.6-1.6dyn. Besides, we were successful in estimating the motive force of that in phototactic migration, whose estimation had not yet been reported. It was estimated as 0.8-2.4dyn, which was about 1.5 times larger than that in the dark. Also, illumination with light from the front increased the motive force, whereas illumination from the back caused quite opposite results. That is to say, light illumination could give direct influence upon their motive force. These results seem to suggest the necessity of taking into consideration the direct effect of light illumination upon the motility of the cells in the migrating pseudoplasmodium. In the present study, for the similar purpose, the effects of the "Artificial gravitation" upon culmination were also investigated by utilizing the centrifugal force. When the "Artificial gravitation" opposing the direction of culmination was increased, the efficiency of culmination decreased distinctly until hardly any cell mass could culminate at about 40-50G. This measured value could be converted to 0.3-1.0dyn, which indicated the motive force of the cell mass in the culminating fruiting body. This value was almost comparable to that of a migrating pseudoplasmodium. Some interesting behaviors of the cell mass concerning culmination under various gravitational conditions were also observed. From these observations, the following suggestions were made. Assuming that the culmination mechanism has two steps, i.e., an upward lifting motion of the cell mass and its elongation, the "Artificial gravitation" seems to affect the upward lifting motion of the cell mass in the culminating fruiting body. Moreover, the motive force of both migrating and culminating might be brought about by similar mechanisms and/or similar types of cells. On the basis of these results, a study on the model to elucidate their collective motions is in progress, and it will be reported shortly.