Minimum degree and the minimum size of K22-saturated graphs

A graph G is said to be F-saturated if G does not contain a copy of F as a subgraph and G+e contains a copy of F as a subgraph for any edge e contained in the complement of G. Erdos et al. in [A problem in graph theory, Amer. Math. Monthly 71 (1964) 1107-1110.] determined the minimum number of edges, sat(n,F), such that a graph G on n vertices must have when F is a t-clique. Later, Ollmann [K"2","2-saturated graphs with a minimal number of edges, in: Proceedings of the Third SouthEast Conference on Combinatorics, Graph Theory and Computing, 1972, pp. 367-392.] determined sat(n,F) for F=K"2","2. Here we give an upper bound for sat(n,F) when F=K"t^2 the complete t-partite graph with partite sets of size 2, and prove equality when G is of prescribed minimum degree.