Share prices made a firm start, benefitting from modest short-covering and futures-linked buying in the wake of the rebound of the March futures contract in Chicago, brokers said. But they turned lower on futures-linked selling as the dollar resumed its fall against the yen. The US currency tumbled to its lowest level for more than two years here, dealers said. In early trade thegreenback touched 110.70 yen. Blue-chip exporters emerged as the main target of selling amid uncertainties about the extent of the yen's appreciation. They said the stock market's slide was expected to have "no serious, negative impact" on economic activity in Japan.