The BSE benchmark Sensex plummeted by over 220 points in opening trade today. The 30-share barometer, which gained 119.32 points in the previous session, was down by 220.70 points, or 1.37 per cent, at 15,844.72 within minutes of the opening bell.The wide-based National stock Exchange Nifty index also fell by 67.45 points, or 1.40 per cent, to 4,744.90.