Japan Airlines Corp.'s $25.5 billion bankruptcy may be the impetus for such companies as Hitachi Ltd. and Toyota Motor Corp., Japan's biggest private employers, to shore up their deficit-ridden pension plans.

Japan's top 278 companies were a combined ¥21.5 trillion behind on their pension funding in fiscal 2009, a 50 percent jump from the previous year, according to Daiwa Institute of Research in Tokyo. Hitachi's unfunded liabilities totaled ¥1.1 trillion — triple the deficit that helped push Japan's former national carrier into bankruptcy.

The pension plans suffer from two decades of slumping markets, an aging population and a dependence on packages that are immune to investment performance. Japan Inc. stuck with defined-benefit plans even as the nation's stock market slid and interest rates hovered near zero.