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

Abstract

A rotary motor in a termite flagellate 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. This study demonstrates directly that the axostyle complex generates torque, and describes several of its dynamic properties. 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 thus a load on the axostylar rotary motor, but the speed of the posterior segment represents the free-running motor. A third, middle segment of the axostyle, not connected to the head or axostylar projection, can also 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 torque. An electric model of the axostylar rotary motor is presented to help understand the length-velocity data.