  We obtain an exact result on single hole dynamics in one-dimensional
Mott-insulators through the study on the supersymmetric t-J model with long
range interaction at half-filling. We calculate the expression G_{1s1h}(x,t)
for one spinon one holon contribution to the hole propagator. We find that
G_{1s1h}(x=0,t=0)=3/8, which amounts to 75% of the spin-fixed mean particle
density 1/2.
