The effects of laser microbeam irradiation on the flagellum of Crithidia (Strigomonas) oncopelti.

The flagellum of the trypanosomatid flagellate Crithidia (Strigotnonas) oncopelti is capable of propagating waves from both its base and tip (Holwill, 1965). In the present study, the capabilities of bend initiation and propagation by the base, tip and points along the flagellum have been studied by observing the effects of irradiation of small regions with a pulsed ruby laser microbeam. The location of the mechanism for deciding the direction of propagation of bends has also been studied by this method. In most flagella for which the waveforms have been examined, bends are initiated at the base and propagated toward the tip (e.g. Gray, 1955, 1958; Brokaw, 1965); they are not propagated in the reverse direction. In certain flagella of this type, namely the sperm tails of some sea urchins and starfish, the ability to initiate bends appears to be localized in a small region at the base (Goldstein, 1969). Rikmenspoel & van Herpen (1969) suggest that the same may be true for bull spermatozoa, but their evidence is not conclusive. In some flagella, however, waves can be propagated from either the base or the tip (Walker & Walker, 1962; Afzelius, 1962; Holwill, 1965). This ability suggests that these flagella have, at least, one initiator region at their base and another at their tip, which may or may not be able to act independently of one another. (Alternatively, all points along these flagella may be capable of initiating bends.) In addition, it implies that a mechanism exists for determining which point on a flagellum will initiate bends at any particular time. The flagellum of C. oncopelti has the ability to propagate bending waves in either direction (Holwill, 1965). In contrast to the sperm mentioned earlier, it usually propagates waves along the flagellum from tip to base, and consequently swims with the flagellum pulling the cell body. If the organism is disturbed by, say, swimming into an obstacle, it can reverse the direction of bend propagation. This flagellum has a typical 9+2 fibrillar ultrastructure (Holwill, 1965; Burnasheva, Ostrovskaya & Yurzina, 1968). Different distributions of initiator activity have been suggested by Brokaw (1966 a) and by Machin (1958, 1963). In the model proposed by Brokaw a single initiator is located at the base, with bending at one point triggering bending at the following point. This model could be modified easily to allow initiation at both the base and tip, • Present address: Department of Physiology-Anatomy, University of California, Berkeley, California, 94720, U.S.A.