Invariant subspaces in some function spaces on symmetric spaces. II

Let $G$ be a semisimple connected Lie group with finite centre, $K$ a maximal compact subgroup of $G$, and $M=G/K$ a Riemannian symmetric space of non-compact type. We study the problem of describing the structure of closed linear subspaces in various function spaces on $M$ that are invariant under the quasiregular representation of the group $G$. We consider the case when $M$ is a symplectic symmetric space of rank 1.