D-branes in NSNS and RR pp-wave backgrounds and S-duality

We investigate boundary conditions for open strings in NSNS and RR pp-wave backgrounds constructed by Russo and Tseytlin, which are S-dual to each other. We show that if we do not turn on any boundary term (i.e. gauge field), D-branes in the RR background cannot move away from the origin in most cases, while those in the NSNS background can move anywhere. We construct RR counterparts of D3-branes in the NSNS background as D3-branes with gauge fluxes and show that indeed they can move anywhere, in accord with S-duality.