Preheat oven to 325 degrees. Grease and flour a 10-inch tube pan or 12 cup Bundt pan. In a large mixing bowl, combine flour, sugar, poppy seeds, butter, buttermilk, eggs, baking soda, baking powder, salt, lemon rind and vanilla. Beat on low speed of electric mixer until ingredients are moistened. Then, beat on medium-high speed for 2-3 minutes, or until ingredients are well combined and mixture lightens and is smooth. Pour batter into prepared pan and bake 45-50 minutes, or until a toothpick inserted in center comes out clean. Cool 10 minutes in pan, then invert onto rack to cool 30 minutes. Meanwhile, make glaze by mixing lemon juice and confectioners' sugar in a small bowl. Drizzle over cooled cake and serve. 349.9 calories, 14 g fat, 5 g protein, 52.1 g carbohydrates, 84 mg cholesterol, 266 mg sodium.