  A class of D-branes for the type IIB plane-wave background is considered that
preserve half the dynamical supersymmetries of the light-cone gauge. The
D-branes of this type are the euclidean (or instantonic) (0,0), (0,4) and (4,0)
branes (where (r,s) denotes a brane oriented with r axes in the first four
directions transverse to the +,- light-cone and s axes in the second four
directions). Corresponding lorentzian D-branes are (+,-;0,0), (+,-;0,4) and
(+,-;4,0). These are constructed in two ways. The first uses a boundary state
formalism which implements appropriate fermionic gluing conditions and the
second is based on a direct quantisation of the open strings ending on the
branes. In distinction to the D-branes considered earlier these have massless
world-volume fermions but do not possess kinematical supersymmetries. Cylinder
diagrams describing the overlap between a pair of boundary states displaced by
some distance are evaluated. The open-string description of this system
involves mode frequencies that are, in general, given by irrational solutions
to transcendental equations. The closed-string and open-string descriptions are
shown to be equivalent by a nontrivial implementation of the S modular
transformation. A classical description of the D-instanton (the (0,0) case) in
light-cone gauge is also given.
