Stir together flour, baking powder, baking soda and salt; set aside.
In large bowl of electric mixer cream butter, 1 cup sugar and orange and lemon peel until fluffy. Add eggs, one at a time, and beat after each until thoroughly blended. At low speed add flour mixture alternately with buttermilk. Fold in walnuts.
Spread batter evenly in greased 9 inch tube pan. Bake in center of preheated 350 degrees F (175 degrees C) oven about 55 to 60 minutes or until pick inserted in center comes out clean, cake shrinks slightly from sides of pan and surface springs back when pressed lightly with finger. Cool pan on rack slightly. In saucepan mix juices, remaining 1 cup sugar and the rum; bring to boil, then pour carefully over cake in pan. Cool, cover; let stand in pan a day or two before serving.