BUENOS AIRES, March 18 (Reuters) - Argentina's stock, currency and bond market trends on Wednesday.
* MerVal stocks index .MERV rose 1.3 percent to 1,065.56 points, following Wall Street and other regional bourses higher after the U.S. Federal Reserve unveiled a surprise plan to buy long-term Treasury bonds to try to revive the economy.
* Locally traded shares in index heavyweight Tenaris TENA.BA, which makes steel pipes for the energy industry, gained 2.6 percent to 35.80 pesos.
* On the broad market volume was weak at $11.9 million. Of active issues 28 advanced, 24 declined and 19 were unchanged.
* Argentine bonds fell 1 percent on average in local over-the-counter trade, suffering a sixth straight session of losses as institutional investors sold off their holdings amid political uncertainty.
* Traders said investors are wary about a renewed standoff between farmers and the government over export taxes, and an unexpected government proposal to move forward mid-term elections by four months to late June.
* The peso-denominated 2033 Discount bond ARDISCP=RASL slumped 2.3 percent, according to the ask price.
* In formal exchange between banks, the peso weakened 0.34 percent to 3.6575/3.66 per dollar ARS=RASL, with the central bank intervening in the market to keep the local currency from sliding further, traders said.
* In informal trade between foreign exchange houses, as measured by Reuters, the peso shed 0.33 percent to 3.7425/3.7475 ARSB=. (Reporting by Jorge Otaola and Walter Bianchi; Writing by Hilary Burke; Editing by Leslie Adler)