Laser microbeam study of a rotary motor in termite flagellates. Evidence that the axostyle complex generates torque.

Abstract

A rotary motor in a termite [Cryptotermes carifrons] flagellate [resembling Caduceia kofoidi] continually turns the anterior part of the cell (head) in a clockwise direction. Previous descriptive observations implicated the noncontractile axostyle, which runs through the cell like a driveshaft, in the motile mechanism. It is directly demonstrated that the axostyle complex generates torque; several of its dynamic properties are described. By laser microbeam irradiation, the axostyle is broken into an anterior segment attached to the cell''s head and a posterior segment which projects caudally as a thin spike, or axostylar projection. Before lasing, both head and axostylar projection rotate at the same speed. After breaking the axostyle, the rotation velocity of the head decreases, depending on the length of the anterior segment. Head speed is not a linear function of axostyle length, however. In contrast, the rotation velocity of the axostylar projection always increases about 1.5 times after lasing, regardless of the length of the posterior segment. Turning the head is a load on the axostylar rotary motor, but speed of the posterior segment represents the free-running motor. A 3rd, middle segment of the axostyle, not connected to the head or axostylar projection, can rotate independently. No ultrastructural differences were found along the length of the axostyle complex, except at the very anterior end; length-velocity data suggest that this region may not be able to generate torque. An electric model of the axostylar rotary motor is presented to help understand length-velocity data.