near infrared laser
Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
The cell of the green alga Mougeotia orients its chloroplast by rotation, according to the direction or polarization of incident red light. The mechanics of the rotation is described by the angle of rotation and the angular velocity of the rotator (i.e., the chloroplast). We developed a laser diffractometer to determine the angle of rotation of the chloroplast. The angle of rotation of the chloroplast shifted by a constant angular velocity, and hence, the net torque on the chloroplast was zero. This suggests that the driving torque acting on the chloroplast is always balanced by the viscous torque. The maximal driving force acting on the chloroplast was estimated to be nearly equal to the force generated by an actomyosin system. This is the first measurement of the driving force acting on the chloroplast in Mougeotia. The amplitude of the force supported the anchorage site hypothesis. However, it remains unclear whether or not the angular independence of the force also supports the hypothesis. © 1992 Wiley-Liss, Inc.
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