I would like to make 3D plot of the following function.

F[x_]:=(x D[EllipticTheta[3, 0, E^(-Pi x)], {x, 2}] + 
      (3/2) D[EllipticTheta[3, 0, E^(-Pi x)], {x, 1}]) x^(5/4))

It did not work with F[1.0]. The error message is: General::ivar: 1.` is not a valid variable.

So I define it as:

    G[y_]:=((x D[EllipticTheta[3, 0, E^(-Pi x)], {x, 2}] + 
      (3/2) D[EllipticTheta[3, 0, E^(-Pi x)], {x, 1}]) x^(5/4)))//.x->y

I can now do:

Plot[F[t], {t, 0, 3/2}]
Plot[F[I t], {t, -Pi/2, Pi/2}]

Is there a proper way to define F[x] without using replacement?