Mitsuo Ishigami

Calcium wave for cytoplasmic streaming of Physarum polycephalum

The plasmodium Physarum polycepharum exhibits periodic cycles of cytoplasmic streaming in association with those of contraction and relaxation movement. In the present study, we injected Calcium Green dextran as a fluorescent Ca2+ indicator into the thin‐spread living plasmodium. We found changes in the [Ca2+]i (intracellular concentration of Ca2+), which propagated in a wave‐like form in its cytoplasm. The Ca2+ waves were also detected when we used Fura dextran which detected [Ca2+]i by the ratio of two wavelengths. We prepared the plasmodial fragment from the thin‐spread and found that the cycles of the contraction–relaxation movement was so synchronized that the measurement of its area provided an indication of the movement. We observed that [Ca2+]i also synchronized in the entire fragment and that the relaxation ensued upon the reduction in [Ca2+]i. We suggest that the Ca2+ wave generated periodically is one of the major factors playing a crucial role in the relaxation of P. polycepharum.

A polarized light and electron microscopic study of the birefringent fibrils inPhysarum plasmodia

SummaryThe birefringent fibrils in thin-spread plasmodium ofPhysarum polycephalum have been investigated with both polarizing and electron microscopes. The birefringent fibrils were classified into three groups by polarized light microscopy. The first type of fibril is observed in the advancing frontal region as a mutual orthogonal array. The birefringence changes rhythmically in accordance with the shuttle streaming. The second type of birefringent fibril is located in the strand region and runs parallel or somewhat oblique to the strand axis. The third type is observed in the strand region always perpendicular to the streaming axis. Electron microscopy confirmed that all these fibrils are composed of microfilaments, which range in densities in the cross view of the fibril from 1.2 to 1.7 × 103/μm2 (1.5 × 103/(xm2 on the average).

Actin cytoskeleton of resting bovine platelets

Actin filaments in resting discoid bovine platelets were examined by fluorescence and electron microscopy. Rhodamine-phalloidin staining patterns showed a characteristic wheel-like structure which consisted of a central small circle connected by several radial spokes to a large peripheral circle. This wheel-like structure was composed of actin filaments forming a characteristic arrowhead structure with heavy meromyosin from muscle. Actin filaments were densely arrayed in parallel with a marginal microtubule band and radiated out from the center to the periphery. Platelets treated with colchicine lost their marginal microtubule band but retained their wheel-like structure and normal discoid form. Cytochalasin B disrupted the wheel-like structure but not the marginal microtubule band or the normal discoid form. After simultaneous treatment with both cytochalasin B and colchicine, platelets lost their discoid shape. These results suggest that actin filaments and microtubules both play important roles in the maintenance of the discoid shape of resting bovine platelets.

Development and evaluation of the flower identification database for mobile with a geo-tagged picture map

We developed a system for creating geo-tagged observational picture maps that makes use of a GPS logger that is equipped with a database of flowers that can be used for the identification of these flowers. This database includes 961 color photographs of 220 varieties of flowers that are commonly found in Japan. The system has the following functionalities: the ability to search and identify flowers by season, color, and name; the ability to view high-resolution video clips showing scenes that are difficult to observe, such as the dispersal of seeds; detailed explanations on the method of identifying similar flowers that are hard to distinguish; and the ability to assist in the creation of an observational picture map by automatically showing photographs together with observational comments on a Google Maps based on GPS signal data. The system was trialed with 208 sophomore university students as part of a fieldwork involving the observation of wild flowers. As a result of the trial, the effectiveness of the system was validated in the following four domains: (1) interest, motivation, and attitude; (2) thinking and decision making; (3) technique and expression; and (4) knowledge and understanding.