The mechanisms of flagellar movement were investigated by studying the ability of various regions of a flagellum to initiate bends, and to propagate bends independently of activities in other regions. Two experimental approaches were used: the establishment of an artificial gradient of ATP along a flagellum, and the inactivation of a small region of a flagellum by localized irradiation. Flagella of the spermatozoa of sea urchins and a few other marine invertebrates were used in this study. Glycerinated flagella were activated by ATP gradients established by means of diffusion from the tips of micropipettes. These gradients could be made broad enough to produce a gradual decrease in ATP concentration along the entire flagellum, or narrow enough to supply ATP to only part of the flagellum. Localized supply of ATP to regions of the flagell11m other than the basal end produced no beating. Beating properties along the flagellum appeared quite sensitive to ATP concentration at the basal end, but rather insensitive to ATP concentration at other points, and centering a gradient about points other than the basal end did not cause beating to start at those points.
Small regions of flagella were irradiated at preselected phases of beating by means of a pulsed ruby laser microbeam. Multiple-exposure dark field photographs of the spermatozoa were taken immediately before and after irradiation. The region of a flagellum between the head and the irradiated point continued beating for at least a few beats if that region was at least a quarter of the length of the tail, and stopped immediately if it was shorter. Bends which were already established beyond the irradiated point continued to the tip, but showed a variety of changes in their properties. No new bends were formed in this region. Irradiation within a bent region caused that region to straighten immediately.
These experiments indicate that the basal end of the flagellum is necessary for bend initiation, and largely responsible for the determination of wave properties. Although a portion of a flagellum can independently propagate established bends, the bend properties at any point are influenced by activities along the rest of the flagellum.
The relevance of these observations to current models of flagellar beating is discussed.
